High speed, energy consumption and emissions

High speed, energy consumption and emissions

Study and Research Group for Railway Energy and emissions

Author: Alberto GARCIA-------------------------------------------Company: FFEFundación Ferrocarriles Españoles-------------------------------------------Document: 1st delivery-------------------------------------------Date: 21 December 2010

RENFE Foto: Patier

INTERNATIONAL UNION OF RAILWAYS (UIC)16 rue Jean Rey - F-75015 PARISTel: +33 (0)1 44 49 20 20Fax: +33 (0)1 44 49 20 29

PASSENGER DEPARTMENT - HIGH SPEED ACTIVITYLegal deposit: November 2010ISBN 978 2 7461 1900 0www.uic.org

High speed, energy consumption and emissions

This report is in response to the contract signed on January 20,

2010 between the Union International des Chemins de Fer (High Speed Committee) and the

“Fundación de los Ferrocarriles Españoles (FFE)”, the aim of

which is to conduct a study entitled "High Speed, Energy

Consumption and Emissions”.

The international Union of Railways The International Union of Railways (UIC known by the acronym of the French Union Internationale des Chemins de Fer) is the global partnership for cooperation among key international actors in the railway sector.

Founded in 1922 with the aim of moving towards standardization and improving systems of railway construction and operation of interoperable, currently holds within it to 171 members, including national railways, operators, infrastructure managers, public transport companies and others.

In recent years the organization has redesigned its objectives and has put special emphasis on issues such as liberalization and globalization of the global rail sector, or the new challenges arising in the rail its key role in a stage of sustainable development and combating climate change.

The main aims of the UIC High Speed Department are to coordinate high speed activities carried out by UIC members and to contribute to logical development of high speed systems. It performs the following activities: updating databases (lines, rolling stock, traffic, etc.), high speed world maps, “benchmarking” and other working teams, communications and contacts, website and high speed brochures as well as other publications.

Fundación de los Ferrocarriles Españoles (Spanish Railway Foundation) The Fundación de los Ferrocarriles Españoles (FFE, Spanish Railway Foundation) was created on February 20, 1985 by RENFE (National Network of Spanish Railways) –currently split into Renfe Operadora and the Administrador de Infraestructuras Ferroviarias (ADIF, Administrator of Railways Infrastructures)- and Ferrocarriles de Vía Estrecha (FEVE, Narrow Gauge Railways). Since 2002 it has been a National Public Sector Foundation.

The mission of the FFE is to promote knowledge and use of the railway through: research and education, technological services, the recovery and alternative use of the railway heritage, cultural activities, periodic publications and specialized books. It also manages the Library, the Railway History Archive and the Railway Documentation Centre, as well as the Madrid Delicias and Vilanova i la Geltrú (Barcelona) Railway Museums.

The Spanish Railway Foundation’s Board of Trustees currently comprises: Renfe Operadora; Administrador de infraestructuras Ferroviarias (ADIF), Ferrocarriles de Vía Estrecha (FEVE), Ferrocarriles de la Generalitat de Catalunya (FGC), Ferrocarriles de la Generalitat Valenciana (FGV), Eusko Tren; Metro de Madrid S.A., Ferrocarril Metropolità de Barcelona S.A., Asociación de Empresas Constructoras de Ámbito Nacional (SEOPAN), MAFEX, Serveis Ferroviaris de Mallorca (SFM), Euskal Trenbide Sarea, Ferrocarriles de la Junta de Andalucía (FJA); Asociación Ferroviaria de Certificación, CETREN and INECO. Department of Research, Training and Cientific Cooperation

The mission of the Department of Research, Training and Scientific Cooperation involves performing activities aimed at promoting the development of the railway, providing the necessary tools for education, promoting the positive image of the railway, and carrying out studies and research projects to serve the interests of the railway sector as a whole, both at home and abroad, and especially in Ibero-American countries.

Its main lines of action are: studies and research projects, sectorial promotion and cooperation, training and communication activities.

The own Department’s research activity is carried out by the following study and research groups:

1. Study and research group for energy and emissions in transport

2. Study and research group for economics and transport operation

3. Study and research group for geography and rail traffic

4. Study and research group for the sociology of transport

In recent years, these groups have worked on many different projects (some completed and others still in progress), the most important being: EnerTrans, ElecRail, Reactiva, Observatorio del Ferrocarril Español (Spanish Railway Observatory), Securemetro, “Hope in Stations”, Viadintel, Aeroave, Balasto artificial (Artificial Ballast), etc.

Table of Contents Table of Contents ......................................................................................................................................................... 5 1. Introduction and background ........................................................................................................................... 7

1.1. The aims of this report ................................................................................................... 7 1.2. Background .................................................................................................................... 8 1.3. Scope of the study ......................................................................................................... 8 1.4. Assumptions and general comments ............................................................................. 9

1.4.1. Electric traction and emissions .......................................................................................................... 9 1.4.2. General comments ............................................................................................................................ 9

2. Does high speed require a lot of energy? ..................................................................................................... 10 2.1. The problem in the www .............................................................................................. 10 2.2. The “square” and “cube” rules ...................................................................................... 10 2.3. Lack of information about the energy consumption of the high speed train? ............... 11

3. Comparison of the high speed railway system and the conventional system in terms of energy consumption ............................................................................................................................................................... 14

3.1. Empirical verification .................................................................................................... 15 3.1.1. Empirical relationship between energy consumption and speed .................................................... 15

3.2. Articles based on specific cases .................................................................................. 18 3.2.1. The case of different trains on different lines .................................................................................. 18 3.2.2. The case of different trains on the same line .................................................................................. 20 3.2.3. The case of the same train on different lines .................................................................................. 20

4. Technical reasons for lower consumption.................................................................................................... 21 4.1. Addends of the consumption function .......................................................................... 21

4.1.1. Energy needed to overcome mechanical resistance on straight track and on curves .................... 21 4.1.2. Energy needed to overcome intake air resistance in the train ........................................................ 23 4.1.3. Energy needed to overcome aerodynamic drag ............................................................................. 23 4.1.4. Energy dissipated by the brake and not utilized .............................................................................. 24 4.1.5. Energy consumed by the trains’ auxiliary services ......................................................................... 28 4.1.6. Multiplier factors in the consumption function ................................................................................. 28 4.1.7. Energy loss coefficient .................................................................................................................... 28 4.1.8. Shorter distances between the same points ................................................................................... 30

4.2. Coefficients and exponents of the consumption function ............................................. 31 4.3. The effect of speed ceteris paribus (all other things being equal) ................................ 33 4.4. Energy used in constructing the vehicle ....................................................................... 34 4.5. General view of the speed´s effect and comparisson with conventional railway .......... 37

5. Analysis of the effect of the shift of traffic from other modes to high-speed rail ..................................... 39 5.1. Modal spilt HS-plane .................................................................................................... 39 5.2. Optimization of speed from the energy consumption point of view .............................. 40

6. Best practices and recommendations in high speed to reduce consumption and emissions ................ 45 6.1. General recommendations (not only for high speed) ................................................... 45 6.2. Best practices applicable to high speed ....................................................................... 46

6.2.1. Increase of speeds on gradients (downgrades) .............................................................................. 46 6.2.2. Optimization of the train’s exterior dimensions ............................................................................... 48 6.2.3. Air intake reduction ......................................................................................................................... 49

7. Bibliography ..................................................................................................................................................... 51

High speed, energy consumption and emissions 2010

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1. Introduction and background The purpose of the study is to identify and quantify energy and environmental characteristics of high speed trains. The study only covers three variables:

1. Final energy consumption. 2. Consumption of primary energy or fossil fuels. 3. CO2 emissions.

Energy differences and advantages of conventional trains in relation to other modes of transport will be observed first, therefore identifying factors inducing train consumption and differences according to train and lines. The characteristics of the high speed system with respect to conventional trains will be analysed next, checking to see whether these accumulate or become diluted with increasing speed, and whether their source is the infrastructure, the vehicle or the operation. Thirdly, we will analyse the effect of the shift of traffic from other modes of transport to high speed trains for varying speeds, checking in each case the effect of consumption on the whole corridor.

1.1. The aims of this report This report analyses the energy consumption of high speed trains and seeks to answer the following questions:

a) Does the high speed system offer the same general advantages as conventional trains?

b) Does the high speed system entail an increase in energy consumption, per passenger, in comparison with the conventional railway system?

c) Does the high speed railway system require less energy, per passenger transported, than other modes of transport?

d) If it requires less energy, what is the order of magnitude of the differences?

e) Does the high speed system’s appearance on a route entail an increase or a reduction in the energy consumption for transportation purposes, taking into account the induced demand?

f) What is the effect of speed on the distribution of the energy used for the vehicle’s construction during its operating life?

In short, the aim is to analyse whether the expansion of the high speed network is going to exacerbate the problem of emissions and energy consumptions in the transport sector; or whether, on the contrary, the high speed railway system is more energy-efficient than other alternative modes and, therefore, investment


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in high speed lines and trains will help improve the sustainability of the transport system.

1.2. Background Thoughts on the widespread opinions regarding the energy consumption and emissions of high speed trains, as well as the evidence which largely contradicts such generally held beliefs, have been published in various previous articles written by members of the “Study and Research Group for Railway Energy and Emissions of the Spanish Railway Foundation”. These publications also contain most of the points covered in greater depth in this report, which relate to the reasons for the differences in consumption between conventional trains and high speed trains, as well as the effect that introducing the high speed train in a corridor has on energy consumption and emissions. Besides expanding on the aspects dealt with in previous publications, this report also adds a number of considerations and data relating to the effect of speed on the amount of energy needed (and on the emissions produced) to manufacture and recycle the train (including the materials incorporated into the train). Another important new feature of this report is the general outline of a method used to quantitatively determine the “optimum speed” of the high speed train from the energy point of view. Both subjects constitute initial outlines which, as has already been done with the topics dealt with previously, would be worth exploring in greater detail in subsequent studies.

1.3. Scope of the study The study aims to have worldwide applicability, given that there are no major differences between countries in terms of the aspects covered in the report. Nevertheless, the study uses data corresponding to the Spanish case, eliminating -obviously- considerations that stem from purely local aspects such as the difference in track gauge between the conventional network and the high speed network. The use of Spanish data offers two advantages:

a) Firstly, all the data used come from the same system (which also provides the authors of the report with abundant data and information), thus avoiding the dysfunctions caused by the use of combined data with an unknown degree of homogeneity.

b) Secondly, the Spanish case includes a unique variety of train types (of different technological origin, architectures and sizes), types of service (long distance, high speed regional trains, overnight trains and trains which partly run on conventional lines), infrastructures (new high speed lines with very different maximum speeds, diverse speed profiles, upgrades, downgrades and unequal path coefficients.


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1.4. Assumptions and general comments 1.4.1. Electric traction and emissions

This report will focus solely on electric traction trains, given that this traction system is the only one that permits high speed running in the sense defined herein, and in order to make homogeneous comparisons it is also necessary to refer to electric traction in the conventional railway system that is to be compared with its high speed counterpart. Otherwise (i.e. if the analysis referred to conventional trains with diesel traction), some of the differences observed would reduce the clarity of the results. Furthermore, all the high speed trains and over 80-90% of the passenger trains currently used in continental Europe are electric traction vehicles. By focusing solely on electric traction, we can analyse energy consumption alone, given that the associated greenhouse gas emissions can immediately be deduced from this energy consumption, since the applicable emission factor is fixed for each year and for each country. Therefore, the train that consumes less energy will be the one that emits less CO2, and precisely in the same proportion. Greenhouse gas emissions will only be analysed when the railway is compared with other modes of transport, most of which use non-electric energy (petroleum products), and there are two reasons for choosing this indicator to measure energy efficiency: the importance of reducing emissions of these types of gases, and the fact that it provides a clear indication of transport’s contribution to the exhaustion of non-renewable energy sources (oil, gas and coal).

1.4.2. General comments It should be pointed out that are no absolute, or universally valid, truths. This study analyses specific cases, corresponding to the European case, in which 30 years’ experience of high speed operation has provided conclusive data. In other types of operation, in other geographic environments, or at other moments in time, the results might be different. It is also worth emphasising that the high speed train is not a substitute for the conventional train, but instead they should seek complementarity. They can and should coexist, and their respective infrastructures and services should be planned in such a way as to ensure that they complement and support each other. During the course of this analysis we will frequently refer to the “train” (in order to use a common and easily comprehensible terminology), but in doing so we are actually referring to the railway as a whole, as a system.


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2. Does high speed require a lot of energy? There is undoubtedly a widespread belief among the general public that the high speed train requires a lot of energy in order to operate, even an excessive and disproportionate amount considering the benefits it provides. This common misconception serves as a pretext to attack the high speed train and propose, as an alternative to constructing new high speed lines, the improvement of conventional lines, or simply the strengthening of other modes of transport.

2.1. The problem in the www An example of the state of opinion on this subject and how these ideas spread through society can be found in some of the entries that Spanish schoolchildren submitted to the Railway Museum’s high speed competition in 2006. In order to find the information they needed, the youngsters searched the Internet and came away with the ideas they felt were most suited to the task. Several entries coincided in reproducing two statements, one of which we have taken directly from an entry submitted by 4th year students at the Gustavo Adolfo Becquer secondary school in Algete (Madrid): “The high speed train consumes a disproportionate and unsustainable amount of energy. The AVE that runs between Madrid and Seville at a maximum speed of 300 km/h (at an average of 209 km/h) has a power output of 8,000 kW: it consumes as much electricity, measured in kilowatts/hour, as a city of 25,000 inhabitants” (sic). Along a very similar line of argument, the 1st year students at the Cardenal Herrera Oria secondary school in Madrid, citing “ecologist” sources, claimed that “increasing a train’s speed from 100 to 400 km/h means that the power has to be multiplied by 64. Yet besides its huge energy consumption (…), it is clear that the AVE is linked to the extremely high consumption of electricity and, therefore, to nuclear energy”.

2.2. The “square” and “cube” rules There are two ideas relating to the links between energy and the railway operation of trains that are very widespread, even among many engineers and railway experts.

a) The first idea, which we could call the “power rule” or “cube rule”, is that the power of the train would increase with the cube of its speed.

b) The second idea, which we could call the “energy rule” or “square rule”, indicates that energy consumption would increase in proportion to the square of the speed. This rule would correspond to a consumption induced solely by quadratic resistances, such as those of an aerodynamic nature.


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2.3. Lack of information about the energy consumption of the high speed train? Roger Kemp, a professor of engineering at the University of Lancaster (Great Britain), has repeatedly insisted on the energy-related harmfulness of the high speed train, with affirmations such as the one contained in this provocatively titled article “Take the Car and Save the Planet” (Kemp, R. 2004) and in ”The European High Speed Network” (Kemp, R., 1993), in which he obtains various comparative results that do no favours at all for the high speed train. The quantitative basis of this professor’s claims is the consumption attributed in 1993 to a hypothetical high speed train running at different speeds between London and Edinburgh. The graph he presented in this study shows an increase closely related to speed, together with some very high energy consumption values.

Figure 1. Comparison between the journey time and the energy consumption of a train between London and Edinburgh for various maximum speeds. Energy is expressed in

kWh/seat and the journey time in hours. Source: Kemp (1993)

With an energy use per seat of 57 kWh for the whole journey, a joint train and transmission efficiency of 65%, and with a power station efficiency of 0.40, Kemp calculates a fuel consumption per seat of 22 litres on the train journey from London to Edinburgh at 350 km/h. He then compares it with a VW Passat 130 TDI carrying two occupants, to which he attributes a fuel consumption of 2.8 litres/100 km (and a “wheel to tank” efficiency of 80%), and reaches the conclusion that the consumption is the same: 822 litres per passenger). He completes the comparison with a single-class Airbus 321-100 to which he attributes a fuel consumption of 16 litres per seat, and with the same “wheel to tank” efficiency (80%), resulting in a consumption of 20 litres per seat for the

1,5

1,7

1,9

2,1

2,3

2,5

2,7

2,9

3,1

3,3

3,5

200 220 240 260 280 300 320 340Maximum speed (km/h)

Jour

ney

time

(h)

30

35

40

45

50

55

60

65

70

Ene

rgy

cons

umpt

ion

(kW

h/se

at)

Journey time

Energyconsumption

3.5

3.3

3.1

2.9

2.7

2.5

2.3

2.1

1.9

1.7

1.5


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journey from London to Edinburgh; in other words, less than the high speed train! It would not be worth analysing these figures any further were it not for the fact that they are practically the only ones to have been published in relation to the high speed train’s energy consumption. Therefore, they have been used by many authors. In view of this, it would seem advisable to point out that Kemp has not taken into account the fact that the same amount of primary energy used to produce electricity does not have the same effect on greenhouse gas emissions or on the contribution to the exhaustion of fossil fuels as when the primary energy used for transportation is derived from oil. In our opinion, the mere comparison of primary energy is not relevant for any practical purpose.

Comparison with Spanish 16-years experience Nevertheless (and disregarding numerous methodological aspects that could be called into question), the most important difference with respect to our own studies lies in the high speed train’s consumption, as Kemp’s 1993 estimate does not seem to tally with Spain’s high speed operation experience over the last 16 years. In fact, let us consider the route from Madrid to Barcelona (620 kilometres, somewhat longer than the London-Edinburgh route used by Kemp) and take a series 103 high speed train with 397 seats running at various maximum speeds. We calculate the journey time with the “Aplica” simulator and the consumption with the Alpi2810 (both extensively checked against actual figures). To ensure homogeneity, the time calculation is based on a margin in the middle of the UIC band (8%); and the consumption is calculated in the train’s wheel-rims (including the auxiliary services) and for each train seat so that the figure 1 shows is strictly comparable. In spite of the greater distance (+3.3%), the result shows:

a) Slightly shorter journey times than Kemp’s (between 6 and 16 minutes), which can be attributed to logical differences, due to the layout of the line or the margins adopted.

b) A considerably lower energy consumption, with differences of up to 56%. The 103 from Madrid to Barcelona, running at 350 km/h, consumes 25,08 kWh per seat in wheel-rims, less than half the figure presented by Kemp, although it should be pointed out that we have assumed the existence (as in reality) of a regenerative brake, whereas this advantage would almost certainly not have been considered in Kemp’s study (based on a 1981 French TGV that did not have a regenerative brake). Yet even without considering the contribution of the regenerative brake, the AVE’s consumption between Madrid to Barcelona, at 350 km/h, would be 27,47 kWh/seat, 52% less than the figure indicated by Kemp.

These differences can be seen in the following table.


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Table 1. Comparison between journey times and energy consumptions at different speeds for a journey from London and Edinburgh (Kemp 2004]) and from Madrid to

Barcelona (independently produced).

Max. Speed (km/h)

Consumption Lon-Edim.

(kWwheel/seat)

Consumption Mad-Bcn

(kWwheel/seat) with reg.brake

Consumption Mad-Bcn

(kWwheel/seat) without re.brake

Time (h) London-

Edimburgh.

Time (h) Madrid-

Barcelona

Time difference MadBcn-LonEdim.

(min)

Consum. Difference

MadBac (with reg brake) - LonEdim. (kWh/p)

Consum. Difference MadBac

(without reg brake) -

LonEdim. (kWh/p)

225 30 16.57 21.77 3.25 3.10 9 -13.43 -8.23

250 36 18.40 23.00 2.95 2.85 6 -17.60 -13.00

300 48 22.00 25.50 2.65 2.50 9 -26.00 -22.50

350 57 25.08 27.47 2.55 2.30 16 -31.92 -29.53

The following graph shows how the differences occur across the whole range of speeds.

Figure 2. Comparison of energy consumption at different speeds for a journey from

London to Edinburgh (Kemp, 2004) and from Madrid to Barcelona (independently produced).

15

20

25

30

35

40

45

50

55

60

65

200 220 240 260 280 300 320 340

Maximum speed (km/h)

Ene

rgy

cons

umpt

ion

(kW

h/pl

aza) Cosump.

LondonEdinburgh(Kemp1993)s 103consumptionMad-Bcnwithout reg.brakes 103consumptionMad-Bcnwith reg.brake

Ene

rgy

cons

umpt

ion

(kW

h/se

at)


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3. Comparison of the high speed railway system and the conventional system in terms of energy consumption In view of this background, we will try to compare the high speed railway’s energy consumption and greenhouse gas emissions with those of the conventional railway. This comparison will be based on empirical verification and results of analyses carried out with simulators, the aim being to explain the reasons for various types of consumption differences. The comparisons entail a difficulty deriving from the fact that the cases being compared are differentiated by other variables (besides speed). In fact, the high speed trains and the lines on which they run are different from the conventional ones; and the differences, besides speed, may relate to the layout, the power supply, the number of stops, etc. As we have explained, the high speed system requires certain curve-free layouts, certain especially light and aerodynamic trains, and a power supply system that can provide high outputs. Without these attributes, high speed would not be possible, and therefore the comparison must incorporate all these attributes. In short, the comparison between the consumptions of the various trains will be made in the normal operating environment of each one: the characteristic lines, their sizes, their occupancy rates... Later on, and in order to understand the reasons for the differences, each one of the causes will be analysed separately in an attempt to attribute parts of the differences to each one of the two categories of consumption inducers (defined by Minayo, 2008): the direct effects of the speed and the effects of the high speed system.


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3.1. Empirical verification An initial approach could involve observing reality from a general perspective, in order to find out whether the “common misconceptions” have any basis in reality or whether, on the contrary, reality offers different results.

3.1.1. Empirical relationship between energy consumption and speed As regards the “common misconception” regarding energy consumption (“square rule”: the energy consumption of the trains would increase with the square of their speed), we have made a comparison between various types of trains that cover a variety of real situations. An initial comparison, of an economic nature, can be obtained from Renfe’s 2005 Report1 by extracting the data corresponding to traction energy use and the income and traffic figures of each one of Renfe’s Business Units. These Units cover commuter, regional, long distance and high speed trains, with relatively different average speeds from one Unit to another, but with a certain degree of uniformity within each Unit. The results appear in the following table, which confirms the existence of an inverse relationship between speed and the percentage of total costs and total income that the energy cost represents. Specifically, in the case of the High Speed Business Unit, whose trains logically have the highest commercial speed2, energy costs account for only 5.25% of income3, as opposed to 16.32% in the freight trains or 12.08 % in the commuter trains.

1 The reason for using the 2005 Report is that it is the last one in which the data corresponding to Suburban, Regional, Long Distance and AVE are presented separately, as these four Business Units have since been grouped together in two areas of activity: “Suburban and Medium Distance” and “Long Distance and High Speed”, the data being published for each area of activity. Moreover, since 2005 the medium distance high speed trains (Avant product) have been managed by the “Suburban and Medium Distance” area, whereas up until then they had been managed by the AVE Business Unit. Therefore, the data contained in the 2005 Report are the last ones with the old structure which, given the high number of different types of trains, offers more relevant information for our purposes. It should be pointed out that the price of energy has risen sharply since 2006, which has increased energy costs as a percentage of income (in 2006, the energy costs for passenger trains accounted for 7.44% of income, as opposed to 6.86% in 2005). However, this does not affect the relationship with speed, which is the purpose of this study. 2 In 2005, the High Speed Business Unit includes both the AVE trains and the Shuttles and “Talgo 200” that partly use the high speed lines. 3 For comparative purposes, it is worth pointing out that in 2007, Iberia (the Spanish national airline) recorded energy costs of 1.144 billion euros, which represents 21.8 % of their operating costs (on all routes) and 20.7% of their operating income; in other words, the aviation energy costs/income percentage is approximately 3.7 times higher than that of the high speed train.


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Table 2. Weith of energy costs on several passenger trains

Average speed Traffic

Traffic income

Income per traffic

unit Engry

expensesTotal

expenses

% Energy / Incomes

% Energy /

expenses

Energy expenses per traffic

unit

km/h Gvkm (Gtkm)

M€ / year

c€/v.km o c€/t.km M€ / year M€ / year

%GE/ GT % GE/ IT

c€/ v.kmt t.km

Commuter 53.29 8,417 574 6.82 69.35 556 12.08% 12.47% 0.82 Regional 71.21 2,745 222 8.10 14.88 216 6.69% 6.88% 0.54 Long distance 89.29 6,322 426 6.73 33.10 480 7.78% 6.89% 0.52 AVE-High speed 159.99 2,325 262 11.26 14.58 276 5.57% 5.28% 0.63 Freight 54.50 11,071 323 2.91 52.68 409 16.32% 12.89% 0.48 Total 69.07 30,880 1,807 5.85 184.59 1,937 10.22% 9.53% 0.60

As the table shows, Renfe’s energy costs represent only 9.53% of the total business income, whereas in other modes of transport, namely the car, the bus and the aeroplane, energy accounts for approximately 50%, 25-30% and 20-30% of the total costs, respectively. In the case of the railway, this percentage has dropped significantly over the years, given that energy costs accounted for 28% of total costs in 1958. The analysis of energy costs in relation to income has a weakness, given that the unit income generated by each traffic unit (passenger-km) varies significantly according to each type of traffic. In fact, income per traffic unit rises sharply when the average speed increases, as can be seen in the table. Even though this inducer (income per passenger-km) offers an example of the passengers’ willingness to pay for an increase in the average speed of the trains (even if they had to pay more for an increase in energy consumption), it is true that from the technical point of view, the amount of energy consumed per passenger-km seems more important than energy costs as a percentage of total income.


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In this respect, the following graph shows how the High Speed Business Unit, the one whose trains run at the highest speed (160 km/h), is precisely the one that records the lowest consumption per passenger-kilometre, whereas in the rest of the business units, the consumption per passenger-km increases as the average speed decreases.

Figure 3. Comparison of energy consumption (Wh) per passenger-kilometre in various

types of trains in ascending order of average speed. Independently produced.

This fact should not come as a surprise, because if we compare various road transport services, the fuel consumption of a car in the urban driving cycle, with an average speed of 40 km/h, is about 60% higher than the same car’s consumption in the intercity driving cycle with an average speed of 100 km/h. The same occurs in the case of buses and coaches: in urban services (20 km/h) the energy consumption is approximately 30% more than on intercity routes with average speeds of around 70 km/h.


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3.2. Articles based on specific cases In recent years, the author has published various articles about the energy consumption of all types of high speed trains with the help of a self-developed energy consumption simulator, practical verification of the resultant data having revealed a high level of accuracy. Some of these articles, together with others produced by other authors, allow the energy consumption of the high speed train to be compared with that of the conventional train in specific cases. We have chosen three cases: one involving different trains (high speed and conventional) on different lines (high speed and conventional); another involving different trains (conventional and high speed) on the same line; and finally, identical trains (high speed) on two different lines (high speed and conventional).

3.2.1. The case of different trains on different lines The first of these articles (García Álvarez, 2005) aimed to analyse the “energy guzzler” accusations that are frequently levelled against the high speed train and the campaigns against these trains that are supported by those who demand, with a view to reducing transport consumption and emissions, the expansion of improved conventional lines or speed limits for trains. Therefore, the article compares the consumptions of the high speed train with those of the conventional train. Thus, by means of simulation validated with real data, the energy consumption of a conventional train (consisting of a series 252 electric locomotive and 7 “Arco” cars) running at 200 km/h on an improved conventional line (Barcelona to Alicante, on what is known as the “Mediterranean Corridor”) was compared with the consumption of a high speed train (Talgo 350, Renfe series 102) on the Madrid-Lleida section of the Madrid-Barcelona high speed line. In both cases, the trains have the same capacity (316 seats). The average speed reached by the high speed train is 32.6 % higher, in spite of which it consumes less energy per kilometre, both when measuring the energy imported to the pantograph (-7.2%) and when recording the net energy (deducting the energy exported to the network) as it leaves the power plant4 (-15.7%). Given the aim of the experiment, the effect of the shorter length of the high speed lines in comparison with the conventional lines was not taken into account (for example, the high speed line is 16.5% shorter in the case of the Madrid-Lleida section), which would make the difference even greater in favour of high speed.

4 The difference between the energy produced at the power station and the energy imported to a train’s pantograph lies in the energy conversion and transmission losses that occur from the moment it leaves the power station to the moment it enters the train, minus the energy regenerated by braking (negative). In short: Energy generated at the power station = Energy imported to the pantograph + losses in the network and catenary – energy regenerated in braking.


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To separate the influence on this result of the train’s characteristics on the one hand, and those of the line and the service on the other, the consumption of the same high speed train (Talgo 350) running on the improved conventional line is also simulated. The difference in consumption turns out to be smaller than in the real case, but the consumption is still lower (-7.4% in power station busbars) in the case of the high speed line. All of which leads to the conclusion that “it cannot be said the energy consumption of the high speed train (at 300 km/h or more) is essentially different from that of the improved conventional train (running at maximum speeds of around 200 km/h), provided that the service characteristics are homogeneous”. The following graph shows the differences between each one of the addends in the consumption of the two trains.

It can be seen that, in spite of a lower average speed, consumption is higher in the improved conventional train, both in the train’s wheel-rims and at the power station outlet. Certainly, consumption due to aerodynamic drag is much higher (+71.6%) in the high speed train, but all the other consumption addends are lower: mechanical resistances (-30.4%), auxiliary services (-28.9%), losses in the locomotive and in the network (-30.7%) and, most of all, energy dissipated in the brake (-57.29%), this being the addend with the biggest reduction in consumption.


20

3.2.2. The case of different trains on the same line Another comparison, between a new high speed train and a conventional train on the same line (albeit improved), can be found in Andersson and Lukaszewicz (2006), who have carried out in-depth analyses of energy consumption in trains in Sweden. These authors show that on the same route (Väterás to Stockholm), a conventional train took 78 minutes and consumed 0.042 kWh/seat-km in 1994, whereas in 2004 the X2000 tilting high speed train, with one more stop, took 53 minutes (-32%) and consumed 0.030 kWh/seat-km (-28%).

3.2.3. The case of the same train on different lines In García Álvarez and Martín Cañizares (2007) we analysed the compared consumption of the same train on two lines (a high speed line and a conventional line) between the same points, and in two specific cases: that of an Alvia 120 train (Renfe series) between Lleida and Roda de Bará, and that of a Talgo 200 between Córdoba and Antequera. In December 2006, these (variable track gauge) trains stopped running on the conventional lines and began to operate on the new high speed lines. In this case, on changing from the conventional line to the high speed line and running between the same stations, the Alvia and Talgo 200 trains achieved energy consumption reductions in the pantograph of 16% and 8% respectively, which is compatible with an average speed increase of 64% and 78% respectively. In the same article we also analysed the consumption of electricity produced by these trains, measured at the power station’s outlet busbars. In the case of Lleida to Roda, the reduction in consumption at the power station is -40%, greater than the reduction measured in the pantograph (-16%). Something similar occurs in the case of the Córdoba route: consumption in the power station bars is 27% less (in the pantograph the reduction in consumption is 8%). The differences are due to the fact that the high speed lines are electrified at a higher voltage (25 kV as opposed to 3 kV), which means that losses are lower. Moreover, the regenerative brake is used more on high speed lines than on conventional lines.


21

4. Technical reasons for lower consumption In all the real cases analysed (different trains and lines; different trains on the same line; and the same train on different lines), the result of the analysis coincides with the overall result observed for all Renfe’s trains: the trains that run at higher speeds consume less energy. As this result clearly contradicts the existing “common misconception”, it is worth analysing in detail the reasons for this lower consumption.

4.1. Addends of the consumption function The train’s dynamics is explained in detail in García Álvarez (2004), and the physical and technical reasons that explain the differences in consumption between the high speed train and the conventional train are analysed in García Álvarez (2006). Using data from both articles we will explain the reasons for the consumption by taking a look at each one of the addends that make up the energy consumption according to the underlying model in the ALPI2810©

simulator. The consumption function is constructed by analysing the energy released by the train, to which we add the losses that occur from the moment the energy leaves the power station to the moment it leaves the train. In each case, we will analyse the relationship with the mass, the distance travelled and the train’s speed, and also with the characteristics of the vehicles and the lines that are necessary for operating at high speed. This will allow us to produce a table, with approximate coefficients, that sums up the different consumption in each one of the parts that explain it.

4.1.1. Energy needed to overcome mechanical resistance on straight track and on curves The energy needed to overcome mechanical rolling resistances depends on the specific value of such resistances, the mass and the distance travelled. Along the whole route (straight and curve) it can be assumed that this resistance is proportional to the train’s mass, the constant of proportionality (a) ranging from 1.2 to 2 daN/t for conventional trains and from 0.5 to 0.9 daN/t for high speed trains. On curves, the energy required is proportional to the mass and to the distance travelled, and inversely proportional to the curve radius. In García Álvarez (2004,[7]) it is proposed that each line be modelled so that it is defined as an equivalent coefficient of curves (ac) that would be added to the specific coefficient of the mechanical resistances. The values of coefficient ac would vary between 1.424 daN/t (Betanzos-Ferrol line) and 0.08 daN/t (high speed


22

line from Madrid to Barcelona). In the Enertrans project5, values of 1.2 daN/t and 0,09 daN/t are proposed for intercity lines and high speed lines, respectively. The value of these mechanical resistances can be assumed, therefore, to be independent of the speed6 and can be expressed as follows:

cc

rm lMRkLMaE ××+××= ∑

And if the specific coefficient of curves ac is defined as:

L

lRk

ac

c

c

×=∑

,

the energy needed to overcome the mechanical and curve resistances for a route of length L can be expressed as

LMaaE crm ××+= )(

Coefficient a depends on the rolling stock (not on the line), being much lower in high speed vehicles. Coefficient ac depends on the line (not on the rolling stock)7; specifically, it depends on the number of curves and on their radius and length. Therefore, this coefficient is lower on high speed lines, given that the most important layout restriction on such lines is precisely the absence of curves, so that the trains can run at high speed. The vehicle mass M does not seem to be closely related (per standard unit of supply) to the speed or the type of line or type of rolling stock. In any case, if there were a relationship, it would be of a lower mass per standard units of supply in high speed trains.

5 The aim of the EnerTrans research project was to obtain an accurate model that reveals the energy consumption (and its associated emissions) of the Spanish transport system, according to the significant variables on which it depends. Participants include the Fundación de los Ferrocarriles Españoles, Universidad de Castilla-La Mancha, Universidad Pontificia de Comillas de Madrid, ALSA, Universidad Politécnica de Madrid–INSIA, Fundación General de la Universidad Autónoma de Madrid, Fundación Agustín de Betancourt and Fundación Universidad de Oviedo. The project is subsidised by the Centro de Estudios y Experimentación de Obras Públicas (Ministry of Public Works, project nº PT-2006-006-01IASM). 6 In France, a part of the mechanical resistances is considered to be proportional to the speed (Bernard and Guiheu, 1976, [6]), but this is not a widespread practice, and the proposed values of coefficient a already include the part that would depend on the speed. 7 For certain specific vehicles, such as the Talgo trains with guided axles, or for certain rolling gear arrangements, the constant kc may depend on the rolling stock, but both trains, whatever the value of kc may be, can run at any speed within their respective speed ranges, and therefore the relationship between kc and the rolling stock will not be taken into account in this analysis.


23

4.1.2. Energy needed to overcome intake air resistance in the train The energy needed to overcome the resistance produced by the entry of air into the train is proportional to the amount of air that enters the train (Q, in m3/s), which is a parameter determined by passenger comfort; to the air density (d); to the train’s speed; and to the distance travelled (L). It can therefore be expressed as follows:

LVdQkE eaea ××××=

where kea is constant. Q is related to the size of the train (number of seats), but is independent of the train’s speed and the type of line it runs on.

4.1.3. Energy needed to overcome aerodynamic drag The energy needed to overcome aerodynamic drag depends on the square of the instantaneous speed and on the air density; it does not depend on the train’s mass. It can be broken down into two addends, one of them due to pressure (normal forces) and another due to friction (shear stresses).

Energy needed to overcome drag due to pressure forces Drag due to pressure forces occurs both at the front and the rear of the train, and depends (with a proportionality coefficient cp) on the train’s cross-section surface area (St), and on its form (coefficient Cx). It also depends on the air density and, on the part of the route corresponding to tunnels, on a tunnel factor (Tf). The energy consumed on the route due to this cause is:

∫ ××××= dlVTfScE fprap2

In conventional trains, the value of coefficient cp is around 0.0022 daN/[(km/h)2.m2], whereas in high speed trains the value is closer to 0.00096 daN/[(km/h)2.m2], assuming a cross-section surface area of about 12 m2 in both cases.

Energy needed to overcome friction drag Friction drag due to shear stresses occurs on the train’s wet surface (“skin”), whose surface area can be calculated on the basis of its height (H), length (Lt) and width (W) as follows:

tm LWHS ×+×= )2(

The energy needed to overcome this drag on a route is:

∫ ××××= dlVTScE fmfraf2

In conventional trains, the value of coefficient cf (which depends on surface continuity and quality) is around 0.00003 daN/[(km/h)2.m2], whereas in high speed trains the value is closer to 0.000021 daN/[(km/h)2.m2], assuming a wet perimeter of 11m in both cases. It should be pointed out that for trains with a length of more than 200 m, the quotient cf tends to fall.


24

For all the aerodynamic drags, Lukaszewicz proposes a coefficient C value proportional to (ρ/2)x(8.3+0.057Lt,) for conventional trains, and a value proportional to (ρ/2)x(4.7+0.050Lt) for high speed trains, Lt being the length of the train in metres. For a 200 metre train, this means that the value of coefficient C in a high speed train is 25.3% lower than the same value in a conventional train

4.1.4. Energy dissipated by the brake and not utilized On any given route, the train needs additional energy to increase its speed and to climb upgrades. However, instead of being lost, this energy accumulates in the train in the form of kinetic and potential energy respectively, and can be used to overcome the rolling resistance, in which case it is not wasted. As the energy needed to overcome rolling resistances has already been considered in the previous addends (whatever their origin may be: external or energy accumulated in the train itself), it can be understood that the energy lost is only that which is dissipated by the train’s brake. This dissipation occurs in two cases: when the train brakes to reduce its speed (in order to stop or comply with a local speed limit) or when it brakes to descend a steep downgrade without exceeding the maximum speed. Therefore, the energy dissipated by the brake is the sum of the energy dissipated by braking to reduce speed and the energy dissipated by braking to descend steep downgrades.

Kinetic energy dissipated in speed reductions The kinetic energy dissipated in speed reductions depends on the vehicle’s mass, the rotating masses8, the distance between technical and commercial stops and the distance between equivalent stops (parameter of the line that characterises the homogeneity of the authorised speed profile -see García Álvarez for more information-).

( ) ( ) LVDDD

MMEptpepc

rotfrepar ××⎟⎟⎠

⎞⎜⎜⎝

⎛++×+×= 2111

21

From this energy we can deduce the amount used to overcome rolling resistance during the deceleration process. The amount of energy dissipated in the speed reduction depends on the mass (and on the rotating masses), the number of stops (Dpc) and the homogeneity of the speed profile (Dpe).

8 Rotating masses are those which turn with a rotation speed proportional to the translational speed of the vehicle (axles, wheels, brake discs, etc.) When the train accelerates, these masses increase their rotation speed, and therefore they must be accelerated angularly. This effect is taken into account by adding the “equivalent rotating masses” (Mre) to the train’s mass. These masses usually have an equivalent value of between 4 and 10% of the train’s tare mass. For more information, see García Álvarez 2004.


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Figure 4. Speed profile on the Mediterranean Corridor. The speed reductions are equivalent to an additional stop every 50 km. Source: García Álvarez, 2005

Figure 5. Speed profile of the Madrid-Barcelona and Madrid-Seville high speed lines, equivalent to a stop every 550 km and 120 km, respectively. The homogeneity of the

speed profile is one of the main reasons for the lower consumption of high speed trains. Source: García Álvarez

Kinetic energy dissipated when braking on gradients with a value greater than pe For a train, the gradient of repose (pe) is defined as the gradient for which the train, without braking or applying traction, maintains a speed equal to its maximum speed on the line section. It is understood that the higher the train’s authorised speed on the line, the greater the gradient of repose is. If the actual existing gradient (pr) is greater than the gradient of repose (pr>pe), the train must brake so as not to exceed the maximum speed, and brake more (the greater the difference pr-pe, the more energy it loses). Therefore, the lower the gradient of repose, the more the train will brake on gradients, i.e. the lower the maximum speed, the more it will brake. Thus, for example, when the authorised speed of a series 102 train on the Madrid – Barcelona high speed line changes from 220 to 300 km/h, the energy dissipated by the brake on gradients is reduced by 32%.

0

50

100

150

200

250

0

2867

9

4322

2

7086

5

8233

0

1259

27

1406

43

1651

72

1738

75

1798

67

1871

88

2011

40

2403

14

2519

96

2747

97

3032

64

3825

40

4122

29

4371

62

4478

28

4655

63

4905

25

5022

25

0

50

100

150

200

250

300

350

400

0 100

200

300

400

500

600

Km

km/h


26

The energy dissipated by the brake on gradients can be expressed as follows:

[ ]( ) Meptpplgfrepend

E ×∑ −××=

where pe is greater as the speed increases.

Energy not lost due to economical driving If the train decelerates or descends the gradients without braking, it can use some (or all) of the accumulated kinetic and potential energy to overcome the rolling resistance; the energy consumed is therefore reduced, since the amount of energy dissipated by the brake is reduced. As a result, however, the train loses time, which means that over the whole route it uses more time than the necessary minimum. This is what is called “economical driving” (usually achieved by “coasting”): the longer the journey time, the lower the energy consumption9. In practice, the effect of economical driving can be modelled as a coefficient, equal to or less than 1, which multiplies the energy lost during the braking process.

( )frependfreparcondecono EEkEf +×= , where 10 ⟨⟨ condeconk

If coasting occurs at high speeds, little time is lost, yet the energy saving is high. At low speeds, if the train coasts instead of braking, a lot of time is lost and yet little energy is saved. Therefore, economical driving can save more energy at high speeds, and therefore the high speed train can cover a considerable part of the route by “coasting” (or “freewheeling”) without losing much time. On a typical high speed line, a time margin of 6% (minimum recommended by the UIC) permits Kcondecon values of around 0.4 to 0.6, whereas on a line where the maximum speed is 160 km/h, with the same margin, values of around 0.8 to 0.9 can be obtained for Kcondecon. The economical driving programme on the Madrid-Seville AVE reduced energy consumption by 8% while at the same time increasing the average speed. A high speed train can “coast” along 64% of the Madrid-Seville route (losing 7 minutes without consuming a single kilowatt-hour), while the Madrid-Toledo Avant train can do the same over 68% of the route, losing just 4 minutes of its minimum running time.

Energy recovered by the regenerative brake If the train has a regenerative brake, some of the energy dissipated by the brake can be recovered: either to be used by other trains, or to be returned to the public power network. Only a part of the energy dissipated by the brake is converted into electricity by the regenerative brake (should it exist), as it is always necessary to use, to a greater or lesser extent, the friction brakes. Friction brakes are used mainly at

9 Besides “coasting”, economical driving also admits other variants (which cannot be analysed in detail in this article), and numerous studies have dealt with the optimization of economical driving according to the track profile, the rolling stock and other circumstances, for example: Lukaszewicz (2001) and Aragón (2005).


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low speeds (for example, between 50 km/h and the stop). Therefore, the part of the energy dissipated by the brake that is converted into electricity is greater at high speed. The energy dissipated by the brake that is not regenerated is:

( )frependfreparcondeconoonNOgeneracifrnoreg EEkkE +××=

The value of the NOgeneración (kNOgenreración) coefficient is 1 if the train does not have a regenerative brake. If it does, the following can be assumed, approximately (Vmáx. being the train’s maximum speed on the line, in km/h):

2max

250V

k onNOgeneraci =

From this formula we can deduce that for a maximum speed of 100 km/h, 75% of the energy dissipated by the brake is converted into potentially usable electricity, whereas if the maximum speed is 300 km/h, this percentage rises to 97%. The actual degree of utilization of the braking energy converted into electricity by other trains depends on the length of the electrical sections (the longer they are, the greater the possibility of recovery), and on the traffic density (the higher the density, the more likely it is that when one train is generating energy with the brake, there is another one that needs it for an acceleration process). In practice, it can be modelled as a coefficient kaprovereg

( )frependfreparcondeconoónNOgeneracienaprovecregdoaprovfrena EEkkkE +××−×= )1(

At high speed, alternating current electrification allows the energy produced by the regenerative brake to be returned to the public network, and (although the railway company is not paid for the energy returned to the network) from the energy efficiency point of view, it can be regarded as utilized energy. Therefore, on AC lines, it can be assumed that Kaprovregen=1, whereas with direct current, if there are no devices for storing energy or returning it to the network, it can reach values of 0.5 to 0.9, depending on the traffic density and the length of the electrical sections. In short, and with regard to the utilization of potential and kinetic energy, the above can be summarised as follows:

• The high speed train has to dissipate less kinetic and potential energy, as it makes fewer stops and can descend downgrades at higher speeds.

• Of the energy it has to dissipate, it can lose a smaller part of it in the brake (for the same journey time), as it can perform economic driving more efficiently.

• Of the energy that, in spite of this, it dissipates in the brake, it can convert a larger part of it into electricity (as the electric brake is more usable at high speeds).

• The energy thus converted into electricity can be utilized to a greater degree; as it can be returned to the power network, the degree of utilization is practically 100%.


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4.1.5. Energy consumed by the trains’ auxiliary services The trains’ auxiliary services are systems that consume energy for technical purposes (compressors, motor ventilators, etc.) or for the comfort of passengers (heating, air-conditioning, lighting, etc.) The energy consumption of these services is proportional to the time during which they operate; and therefore, if the average speed increases, the consumption per kilometres decreases in the same proportion as the average speed increases. The energy consumed by the auxiliary services can be modelled as the result of the average power used by the auxiliary systems multiplied by the time during which they operate.

VLkPTkPE usoauxusoauxconfortaux ××=××=

In principle, the energy consumption of the auxiliary services is not directly related to speed; thus, in the verification of a typical high speed case, a 50% increase in the average speed means a 29% reduction in the energy consumed by the auxiliary services. It should be pointed out that the auxiliary services continue to consume energy during stops, even though the train does not cover any distance at all, and therefore an increase in this time (including the time at the passenger’s disposal before the train sets off again) means a higher consumption per kilometre on the part of the auxiliary services. As high speed trains make fewer and shorter stops than conventional trains, and as the time spent at the terminus is divided among more kilometres, the energy consumed by the auxiliary services is also reduced for this reason.

4.1.6. Multiplier factors in the consumption function So far we have specified the addends that make up the consumption function, and the sum of all of them (with their sign) provides the net energy consumed in the train’s wheel-rims (or at the inlet of the auxiliary services) to move the train over a distance of one kilometre. To find out the total energy consumed, we would have to multiply by the energy loss coefficients from the moment the energy leaves the power station to the moment it reaches the train, and also by the total distance travelled.

4.1.7. Energy loss coefficient Power stations have to produce an amount of energy for a train which is the net energy required at the train’s wheel-rim (or at the inlet of the auxiliary services) plus the losses of any kind that occur until the electricity is converted into energy that can eventually be used. Two main types of losses can be identified (each one with an associated loss coefficient): in the power networks and in the locomotive.


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Energy lost in the power networks The energy lost during the voltage change processes and during the transmission of the energy from the power station to the train is proportional to the energy that reaches the locomotive, and the loss coefficient depends on the train’s operating voltage (higher voltage means fewer losses), and also on the electrification characteristics (cross-section of the conductors, distance between substations, etc.) The diagram in Figure 8 shows the equivalent efficiencies in each one of the energy transformation phases and, consequently, the incremental amount of energy that needs to be produced in order to offset these losses. In Spain, high speed lines are electrified at 25 kV a.c. and conventional lines at 3 kV d.c. The higher voltage means fewer electrical losses during the transformation and transmission processes. The additional amount that has to be produced, on top of the amount consumed by the pantograph, is: 22.6 % for trains operating at 3,000 V d.c. and 8.8% if the trains operate at 25 kV, a.c. (Pilo, 2006).

Figure 6. Losses during the voltage change processes and transmission of electricity to

the train. Source: Pilo (2006)

Energy lost in the locomotive In motor vehicles, energy losses occur due to the efficiency of the various systems (converters, reducer motors, etc.) In principle, efficiencies in electric traction vehicles are usually independent of the engine operating conditions, and therefore of the speed and the speed profile. In practice, however, there are fewer energy losses in high speed systems, given that, on the one hand, engines tend to be bigger (and the bigger the engine, the fewer the losses) and, on the other, the modern technologies


30

that are usually applied to high speed trains generally make better performances possible.

4.1.8. Shorter distances between the same points In all the addends of the consumption function, the distance travelled is multiplied by the corresponding monomial. Therefore, it can be said that the energy consumed by a train is proportional to the distance travelled10. High speed layouts imply shorter distances than those of conventional lines between the same points. If the distance is shorter between the same points, energy consumption will be lower in same proportion, all other factors being equal. Table 3. Comparison between distances by high speed line, by conventional railway line,

on straight track (“displacement”) and by road on Spanish high speed routes. Source: García Álvarez and Fernández González (2008)

Displacement Road Conv. R HS R HS R/ Conv. R/ HS R/ HS R/ Madrid to (km) (km) (km) (km) disp. disp. Conv. R road.

Segovia 63.0 96.0 101.6 68.3 1.08 1.61 0.67 0.71 Valladolid 153.0 206.0 249.4 179.2 1.17 1.63 0.72 0.87 Barcelona 502.3 617.0 708.0 621.0 1.24 1.41 0.88 1.01 Zaragoza 260.0 309.8 338.0 306.7 1.18 1.30 0.91 0.99 Lleida 370.0 461.6 532.0 442.0 1.19 1.44 0.83 0.96 Camp. Tarragona 410.0 461.6 595.0 521.0 1.27 1.45 0.88 1.13 Huesca 320.0 380.4 421.0 392.0 1.23 1.32 0.93 1.03 Cuenca 130.0 169.8 200.0 188.1 1.45 1.54 0.94 1.11 Albacete 221.8 266.0 278.7 314.0 1.42 1.26 1.13 1.18 Valencia 301.2 354.0 489.1 390.8 1.30 1.62 0.80 1.10 Alicante 360.0 420.0 454.7 483.0 1.34 1.26 1.06 1.15 Murcia 350.0 400.0 459.9 525.0 1.50 1.31 1.14 1.31 Toledo 66.2 89.6 90.2 75.2 1.13 1.36 0.83 0.84 Sevilla 387.0 535.8 571.0 470.5 1.22 1.48 0.82 0.88 Córdoba 277.0 398.4 440.0 343.0 1.24 1.59 0.78 0.86 Ciudad Real 150.0 208.3 262.0 173.0 1.15 1.75 0.66 0.83 Málaga 393.0 535.3 633.0 512.9 1.31 1.61 0.81 0.96

HSL 1 (North) 1.13 1.62 0.70 0.79 HSL 2 (Northeast) 1.22 1.38 0.88 1.02 HSL 3 (Levante) 1.40 1.40 1.01 1.17 HSL 4 (Andalusi) 1.21 1.56 0.78 0.87

Static HSL AVERAGE 1.26 1.47 0.87 1.00 EFFECTIVE HSL AVERAGE (Weighted with passenger-km) 1.27 1.45 0.88 1.01

The table with data taken from shows that, in Spain, the average distance of high speed lines is 13% shorter than that of the conventional line between the same points, if measured in static terms (as a simple average of the route coefficients), and 12% if the effective route coefficient is measured (the coefficients weighted by the passengers-kilometre anticipated on each route). It

10 Strictly speaking, it would be necessary to add the energy consumed by the auxiliary services while the train is stationary but with these services operating; for example, during commercial stops or the period during which passengers board the train before it departs from the station of origin, or while they get off the train at the destination.


31

can be seen that on some routes (such as Madrid to Segovia) the high speed distance is as much as 23% shorter, and only on certain Levante routes (Albacete, Murcia, Alicante) is the high speed distance greater, due to the peculiar trunk topology of this high speed line.

4.2. Coefficients and exponents of the consumption function The development of the consumption function shows that each one of the addends has a different relationship with the high speed system:

• In some addends, energy consumption is directly related to speed: it increases with speed (e.g. energy consumed due to air intake); or with its square (energy consumed to overcome aerodynamic drags); or it decreases linearly with speed (as in the case of the energy consumption of auxiliary services).

• In other cases, the relationship between consumption and high speed does not derive directly from speed, but from the characteristics of some of the high speed subsystems (of the vehicles, of the infrastructure or of the operating system).

To analyse the reasons for the consumption differences between a high speed train and a conventional train, it is advisable to bear in mind that the fundamental differences between the two types of systems manifest themselves in three areas: rolling stock; different layout and new infrastructure, as opposed to improvement of the existing infrastructure; and a different form of operation (fewer stops). The high speed train is a system, and therefore it should be analysed as a whole. It is not worth comparing only some of its variables (we would reach the conclusion that minimum consumption occurs with very light, modern and expensive trains on lines with favourable layouts and by operating them at very low speeds and with no commercial stops, but then we would have to ask ourselves why a line and train of these characteristics has been constructed/manufactured). In turn, the differences (in rolling stock, infrastructure and operation) between the high speed system and the traditional railway system can be divided into two categories:

• Some differences are intrinsic to high speed: either in the vehicle (lower mass per seat, lower specific rolling resistance), or in the infrastructure (larger curve radii), or in the operation (fewer stops).

• Other differences usually arise due to the greater modernity of high speed lines, although conventional lines and trains should not be excluded from them, at least in the medium term (e.g. alternating current electrification with higher voltages, use of the regenerative brake, greater vehicle efficiency, greater utilization of the trains, etc.)

If we consider the characteristics of the rolling stock, using the abbreviation “CT” to refer to a train with the characteristics of conventional train, and “HST”


32

for a generic train with the typical characteristics of high speed trains, we can analyse each one of the addends and each one of the multiplier factors of the consumption functions to work out the approximate absolute or relative values corresponding to all four possible combinations: high speed train on conventional line (CL), conventional train on high speed line (HSL), high speed train on high speed line, and conventional train on conventional line. We also analyse the relationship of each addend (according to its physical nature) with the mass and the speed.

Table 4. Values of consumption function coefficients and speed exponents in each monomial. Independently produced

Coefficientes: abosolute values Coef. Relative values/LC-TC Exponents

Line and vehicle characteristics CL-CT CL-HST HST-CT HSL-HST CL-CT CL-HST HSL-CT

HSL-HST Leng Mass Spd

Ermr mechanical straight resistance 1.2 a 2 1.2 a 2 0.5 a 0.9 0.5 a 0.9 1 1.00 0.44 0.44 1 1 1

Ermr mechanical curve resistance 0.25 0.25 0.09 0.09 1 1.00 0.36 11.11 1 1 1

Total E. mechanical resistance 1.825 1.825 0.79 0.79 1 1.00 0.43 0.43 1 1 1

Eea resistance to aire intake 0.034 0.034 0.034 0.034 1 1.00 1.00 1.00 1 0 1

Erap resistance to aerod. Presure 0.0022 0.00096 0.0022 0.00096 1 0.44 1.00 0.44 1 0 2

Eraf aerodin. Resistance 0.00003 0.000021 0.00003 0.000021 1 0.70 1.00 0.70 1 0 2

Efp losses of brake on stops 1 0.72 0.42 0.31 1 1 2

Efp losses of brake on slopes 1 0.79 0.39 0.20 1 1 -1

Er energy regenerated by brake 1 0.71 0.40 0.29 1 1

Eaux energy consumed by aux. 1 0 -1

Current and brake charact. C.C.-No

R.B. C.C.-R.B. C.A-

No.R.B. C.A.-R.B. C.C.-No

R.B. C.C.-R.B.

C.A.-No.R.B.

C.A.-R.B.

Brake recovery 0.35 1 0.35 1 1 2.86 1 2.86

Losses in the network 12317 12.317 11.016 1.02 1 1 0.89 0.89


33

4.3. The effect of speed ceteris paribus (all other things being equal) From all the above it can be deduced that if all the other variables remain identical, both those of the infrastructure (speed profile, supply voltages, plan and elevation of the line…), and those of the train (mass, size, form, efficiency…), energy consumption increases as the maximum speed and average speed increase. In order to quantify this increase and assess its economic effects, we have carried out the simulation exercise consisting in “rolling” a series 103 high speed train (397 seats, with 70% occupancy) between Madrid and Barcelona at various maximum speeds (300, 330 and 350 km/h), obtaining in each case (with the Aplica simulator) the minimum time and the commercial time (adding to the minimum time a margin of 13 minutes, which is in the middle of the band of the UIC’s recommendations on margins). The average speed has been calculated and, with the ALPI2810 simulator, the energy consumption measured at the substation inlet (which is where the economic value of the consumed energy is measured). For each one of the stages, the journey reduction times are compared with the increase in consumption and with the value of the incremental energy needed for each passenger. This value, in turn, is compared with the average ticket price. The results appear in the table.

Table 5. Effect of increase in speed (ceteris paribus) on journey time, energy consumption and economic cost on the Madrid-Barcelona route

MADRID-BARCELONA Max. Speed (km/h) 300 330 350

Minimum min 137 129 124 Commercial running time (Margen 13 min) min 150 142 137 Average speed km/h 248.4 262.4 272.0 Substation entry consumption kWk 12,436 13,205 13,795 Time saved on previous min -8 -5 Additional energy on previous stage kWh 770 589 Additional energy per passenger Mad-Bcn kWh 2.58 1.98 Additional energy cost per passenger €/passenger 0.19 0.15 Ad. Energy cost as percentage of average ticket 0.16% 0.12% Underlying time €/h 1.45 1.78 AVE Madrid-Barcelona, direct, serie 103, 397 seats, 70% occupancy Average ticket 120€. Marginal cost 7.5 c€/kWh

From the table we can deduce that: On increasing the maximum speed from 300 to 330 km/h (+10%), the average speed increases by 5.6% and consumption by 6.2%. On increasing the maximum speed from 330 to 350 km/h (+6.1%), the average speed increases by 3.6% and consumption by 4.4%. Therefore, we see that consumption (all other variables being equal) does not increase with the square of the average speed; instead, it increases almost linearly (exactly in proportion to Vmd1.09 and Vmed1.01).


34

In the first stage each passenger would have to pay 29 eurocents to gain 8 minutes of journey time, and in the second stage each passenger would have to pay 15 cents more to gain an extra 5 minutes. This means time values of 1.45 and 1.78 c€/h, considerably lower than those shown in all the analyses of demand, in which case it can be assumed that all the passengers would be willing to pay these amounts, which would represent ticket price increases of 0.16% and 0.12%.

4.4. Energy used in constructing the vehicle The energy used (and the emissions produced) during the vehicle construction or manufacturing process (including all non-recurrent processes such as extraction and transformation of materials, intermediate transport operations, vehicle assembly and scrapping at the end of the vehicle’s operating life, subtracting the energy value of the materials recovered in the break-up) must be divided by the distance covered during the train’s operating life, and also by the seats offered, to obtain the energy (and emissions) repercussion of vehicle construction.

Manufacturing energy Thus, the energy component of vehicle construction or manufacturing, per seat-kilometre, will be:

kmseatkWhRs

densityenergymanmasstrainkilometreseatperenergyingmanufactur ./..×

×=

where: “train mass” in kg; “manufacturing energy density” in kWh/kg; “s” is the train’s number of seats; and “R” is the distance covered by the train during its operating life (in km) The manufacturing energy density (for each ton of the train’s mass) train depends on the type of materials used, but not on the train’s speed. It can be assumed that a vehicle is used for about 7 hours on an average day, regardless of its running speed. Therefore, the distance covered by a train during its operating life is approximately proportional to the average speed. As the distance covered by a train during its operating life increases with speed, the repercussion of energy consumption (per seat-kilometre) decreases with the average speed of the service increases.

Manufacturing emissions Similarly, the emissions per seat-kilometre will be:

kmseatkgCORs

factoremissionmanuCOmasstrainemissionsringCOManufactuu ./.2

22 ×

×=

Where:


35

“Train mass” in kg; “CO2manufacturing emission factor” in kg CO2 per kg; s in the train’s number of seats; and R is the distance covered by the train during it´s operating life (km) If we focus on the case of a high-speed train (30 tons for example), the energy consumed in the manufacturing process is 31,902 kilowatts per ton and emissions generated are 6,325 per ton kilograms CO2.

Manufacturing energy and emissions on several transport modes The energy needed and the emissions produced on manufacturing the vehicle differ from one mode of transport to another.

Table 6. Consumption by seat kilometre depending on the transportation mode

Consumption per ton

Emissions per ton

Kilómetres useful life

Consumption in manufacturing per

seat·km

(kWh/t) (kgCO2/t) (km) (kWh/seat(ton*)·100km) (l/seat (ton*)·100km)

Cars (diesel) Cars 25,497 4,818 200,000 0.42 Road 25,497 4,974 200,000 0.43

Cars (fuel) Cars 25,494 4,818 200,000 0.44

Roads 25,497 4,818 200,000 0.30 Motorbikes Scooter 26,977 5,183 150,000 0.11 Bus Bus 22,973 4,952 1,000,000 0.061

Train High Speed 31,902 6,325 15,000,000 0.23

Freight 20,883 4,642 3,250,000 2.9·10-4(*) Boat Container 18,531 4,567 3,000,000 2.5·10-4(*) Aircraf 46,265 89,373 55,000,000 1.942·10-3

(*) kWh per capacity unit ton in 100 km

Comparison between manufacturing and operating energy and emissions In the case of a Spanish high-speed train class 100 (Alstom) with an average tare of 392.6 tons, 332 seats and 14,052,500 miles covered in its operating life, the percentage of energy consumption in manufacture with regard to the energy consumed in the operating phase is approximately 4,87 %.


36

Table 7. Energy consumption in manufacture in the case of high-speed train in the 100 series

Energy

Obtaining materials (MJ/veh) 26,615,706

Assembly (MJ/veh) 9,869,291

Scrapping (MJ/veh) 266,157

Total (MJ/veh) 36,751,154

Consumption per weigth (kWh/kg) 31.90 Consumption in manufacturing total (kWh) 12,524,742 Consumption in manufacturing total per seat (kWh)/Seat 37,725

Consumption in manufacturing per seat kilometre (kWh)/Seat·km 0.00268 Consumption on the operation per km kWh/km 14.92 Consumption on the operation kWh 209,663,300 % the Consumption in the obtaining materials % 3.53 % the Consumption in the assambly % 1.31 % the Consumption in the scrapping % 0.04 % the Consumption in the manufacturing total % 4.87

Knowing that this train has a consumption of 14.92 kilowatt hours per kilometre in the operating process, energy consumption in the manufacturing (and recycling) process is equivalent to what the train would consume in its operating phase over 684,226 kilometres. Since the high-speed train analysed covers 412,675 kilometres per year on average, energy in manufacturing is equivalent to what it consumes in its movement in 1.65 years.

Relationship with average speed Consumption and emissions in the manufacturing process depend on the materials used in vehicles and their weight, but not the speed at which it then runs. Since consumption generated and emissions must be attributed per seat kilometre, these emissions and consumption levels are divided by the average annual distance travelled by trains. Since the average annual distance covered by trains increases as their average speed of movement increases, energy consumption produced in manufacturing decreases. So, for example, supposing 25 years-life for the train, in the case of a high-speed train with a maximum speed of 250 km/h, energy consumption distribution in manufacturing of 29.116 kWh/km and emissions of 5.773 kgCO2/km, if this maximum speed increases to 300 km/h, the consumption level in manufacturing (and scrapping) changes to 24.738 kWh/km and emissions to 4.905 kgCO2/km.


37

Table 8. Incidence of train speed on the distributions of the energy used in construction

V max. Distance covered

operating life Consumption in manufacturing

Emissions in manufacturing

km/h km kWh/km kgCO2/km

200 7,381,768 1.383 0.274 210 7,667,514 1.331 0.264 220 7,952,883 1.284 0.255 230 8,229,468 1.240 0.246 240 8,497,579 1.201 0.238 250 8,765,565 1.165 0.231 260 9,025,405 1.131 0.224 270 9,285,188 1.099 0.218 280 9,629,084 1.060 0.210 290 9,972,980 1.024 0.203 300 10,316,875 0.990 0.196 310 10,660,771 0.958 0.190 320 11,004,667 0.928 0.184 330 11,348,563 0.900 0.178 350 12,036,355 0.848 0.168

Figure 7. Imputation of energy in terms of life

4.5. General view of the speed´s effect and comparisson with conventional railway In the figure are shown the influence of the speed on the several monomions of the energy consumption function.


38

As can be seen, there are terminus not related with the speed, other increase lineally with speed, others have a cuadratic relationship and, finally other decrease with speed.

Figure 8. Train energy consumption and relationship with speed

(K1+Cc) x (M/s) x V0

MECHANICAL RESISTANCE

K2 x V1

AIR INTAKE RESIST.

K3x(C/s) x V2

AERODYNAMIC RESISTANCE

K4x(M/s)x(1/SD)x V2 ] x (1-RgC)

DECELERATEBRAKING LOSSES

MANUFAC. ENERGY

+ + + +ANCILLARY SERVICES

K6 x V-1

DOWNHILLINGBRAKING LOSSES

[K5 x (M/s) x V-1]x(1-Rg) +

TRAIN&INFR. LOSSES

ρT x ρi

]X[[[ ]+

K7 x V-1]x

LOAD FACTOR(p.km / s.km)

TRAJEC. COEFF.(act.km /ort.km)

Train energy consumption (per seat and orthodromic kilometer) and relationship with speed

+

H S O P E R A T I O N S Y S T E M

H S R O L L I N G S T O C K

H S I N F R A S T R U C T U R E


39

5. Analysis of the effect of the shift of traffic from other modes to high-speed rail When air services exist on a route, the largest part of the emission reductions comes from the travellers the train attracts away from the plane. The train’s share of the market in relation to the plane over distances of 400 to 900 km depends on the train travel time.

5.1. Modal spilt HS-plane In the following graph we can see a characteristic curve that shows that when the train has a journey time of less than 2 hours, it always obtains market share over 85%; and if the journey time is more than 3 hours, the market shares falls below 50%. The graph shows the train’s share of the train+plane market on various European routes (prepared with data taken from Barrón, 2007, and completed with Spanish data).

Figure 9. Relationship between the train’s share of the train+plane market and the

journey time on the main world and Spanish routes with distances of between 400 and 600 km. Source: Barrón (2007) and independently produced

The points that correspond to each one of the cases have been joined by a third degree polynomial fit line, whose equation is:

5.4089182.41686.4´ 23 +×+×−×= TTTsharesTrain

y = 4,686x3 - 41,182x2 + 89,21x + 40,559

20

30

40

50

60

70

80

90

100

1 1,5 2 2,5 3 3,5 4 4,5 5Train travel time (hours)

Trai

n sh

are:

Tra

in/(T

rain

+pla

ne) (

%)

1 3 3.5 4 4.5 52 2.51.5


40

If we assume that the time (T, in hours) is the distance by railway (L in km) divided by the speed (V, in km/h), and P being the annual number of passengers (train and plane combined), the number of train passengers is:

)5.4089182.41686.4(100 2

2

3

3

+×+×−××=LV

LV

LVPpassengersTrain

5.2. Optimization of speed from the energy consumption point of view From the foregoing it can be deduced that at low speeds, increases in the train’s speed produce (due to transference of traffic) emission reductions on a corridor providing there is competition with the plane. This is because a speed increase at low speeds produces a more than proportional (or at least proportional) increase in the train’s market share in relation to the plane, and an increase in the train’s speed produces a moderate increase in its absolute energy consumption. However, high speeds produce market share increases which are less than proportional to the train’s increase in speed (especially in the case of journey times of under 2.5 or 2 hours); and furthermore, at high speeds there are significant increases in emissions when the train’s speed increases. It can therefore be deduced that an “optimum speed” will exist in each corridor from the emission point of view, this being the speed above which there will be no additional reductions in energy consumption and emissions when the train’s speed increases. Obviously, this “optimum speed” only affects energy consumption and emissions, and there are other “optimum speeds” from the point of view of operating costs, attracting passengers, total or external costs, etc. The decision regarding the choice of the “system’s optimum speed” will depend in each case on a multi-criteria analysis in which the optimization of speed from the energy point of view is just one of the criteria to be taken into account. The optimum speed from the emission point of view is different for each corridor, since this optimum speed depends on the length of the route by train, the emissions per plane passenger on the specific route in question, the function that relates the emissions per passenger to the train’s speed, the emission factor of the electricity in the country and year in question, and the train-plane modal split function.


41

As regards the variation in energy consumption (and therefore in emissions) on varying the high speed train’s maximum and average speed, the following order of magnitude can be estimated -all other factors being equal- for a typical Spanish case:

Μ××= 8805.0

412371.0 VE

MP

Where:

PME is energy imported en pantógraph (kWh/km.train)

M is the train mass (in t) and V is average speed (in km/ h)

Case example The ideas outlined above have been applied, by way of example, to the Madrid-Barcelona route to find out, by applying the above methodology, the maximum (and average) speed from which an increase in train speed results in increased emissions in the corridor. Emissions per passenger on the plane are estimated at 70 kg CO2 per passenger (García Álvarez, 2007) and are independent of train speed.

Table 9. The energy consumption of a train has been calculated for different speeds according to the average speed (imported and net in the pantograph) and its C02

emissions per passengers. Maximum speed (km/h) 200 220 240 260 280 300 320 340 360 380 400 420

Average speed without stops

(km/h) 160.8 176.1 191.3 206.4 221.3 236.1 250.8 265.4 279.8 294.1 308.3 322.4

Energy intaken at pantograph level

(kWh/km) 10.67 11.49 12.39 13.37 14.44 15.57 16.78 18.04 19.36 20.75 22.22 23.76

Net energy (kWh/km) 9.52 10.39 11.34 12.35 13.45 14.63 15.88 17.20 18.59 20.05 21.58 23.17

Energy recovered (kWh/km) 1.15 1.09 1.05 1.02 0.99 0.95 0.90 0.84 0.77 0.70 0.64 0.58

CO2 emissions (kgCO2/passenger) 8.95 9.77 10.66 11.61 12.65 13.75 14.93 16.17 17.48 18.85 20.29 21.79

From these data we obtain equations linking energy consumption to average train speed.


42

Figure 10. Energy intaken at pantograph and net energy per kilometre

The points obtained have been joined by a second degree polynomial, the equation for imported energy being:

( ) trainintaken MassVVE ××+××−××= −−− 2527 10163.210787.210867.5 [kWh/km]

And for the net energy:

( ) trainnet MassVVE ××+××−××= −−− 2527 10749.110611.210867.5 [kWh/km]

For a train with 318 seats, assuming a load factor of 0.65, an emission factor of 337 g C02/kWh (Spain, 2007) and a distance of 620 kilometres by rail, emissions per train passenger change with the speed as follows:

Figure 11. CO2 emissions (kgCO2/passenger)

6,00

8,00

10,00

12,00

14,00

16,00

18,00

20,00

22,00

24,00

26,00

120 140 160 180 200 220 240 260 280 300 320 340

Eneergy consumption per km (kWh/km)

Average speed without stops (km/h)

Energy imported in the pantograph Net energy

16.00

18.00

14.00

12.00

10.00

8.00

6.00

20.00

22.00

24.00

26.80

280260240220200180 300160 320 340140120

y = 0,0002x2 ‐0,0084x + 5,6055

3,00

5,00

7,00

9,00

11,00

13,00

15,00

17,00

19,00

21,00

23,00

120 140 160 180 200 220 240 260 280 300 320 340

CO2emissions (kgCO2/passenger)

Average speed without stops (km/h)

CO2 emissions

23.00

Y = 0.0002x2 - 0.0084x + 5.6055

19.00

17.00

15.00

13.00

11.00

9.00

7.00

5.00

3.00

21.00

120 140 280 300 320 340180 200 220 240 260160


43

The points obtained have been joined by a second order polynomial, whose equation is:

6055.50084.00002.0 2 +×−×= VVEmissions [g CO2/passenger]

From the data for emissions per passenger on the plane (Ep, in tons) and the train (Et, in tons), annual passengers in the corridor (P=5,000,000) and average train speed, which determines market share (TS, en %), it is possible to estimate the combined emissions of the train and the plane on the route studied:

By taking the common factor:

( )( )tptp ETSETSPEmissions ×+×−×=+ 100100

By substituting the known values:

( )( )ttp ETSTSEmissions ×+×−×=+ 70100100

000,000,5

By substituting TS and Et by equations that link them to the average speed of the train and knowing that the train distance between Madrid and Barcelona is 620 kilometres:

( )⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

+×−×

×⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟

⎠⎞

⎜⎝⎛×+⎟

⎠⎞

⎜⎝⎛×−⎟

⎠⎞

⎜⎝⎛×

+×⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟

⎠⎞

⎜⎝⎛×+⎟

⎠⎞

⎜⎝⎛×−⎟

⎠⎞

⎜⎝⎛×−

×=+

6005.50084.00002.0

5.4062089620182.41620686.4

705.4062089620182.41620686.4100

000.50

2

23

23

VV

VVV

VVV

Emissions tp

By deriving this equation we obtain the peak at an average speed 284.983 km/h. And for 284.983 km/h average speed, the maximum speed is 367.412 km/h, and this one is, in this particular case, the optimum speed form the energy consumption ad emissions point of view.

⎟⎟⎠

⎞⎜⎜⎝

⎛×⎟⎠⎞

⎜⎝⎛+×⎟

⎠⎞

⎜⎝⎛ −

×=+ tptp ETSETSPEmissions100100

100


44

Figure 12. Annual emissions of train+plane depending on train average speed

145.4

153.1 301.2

308.3

315.4

322.4

329.4258.1

265.4

272.6

279.8

287.0

294.1

213.9

221.3

228.7

236.1

243.5

250.8

176.1

191.3

198.9

206.4

183.7

160.8

168.5

250,000

175,000

150,000

125,000

100,000

75,000

50,000

25,000

225,000

200,00


45

6. Best practices and recommendations in high speed to reduce consumption and emissions

6.1. General recommendations (not only for high speed) The previous sections of this report have explained the inducers of the consumption and emissions of trains in general and of high speed trains in particular. In view of this, it is easy to deduce which line design, train design and operation measures could be adopted to reduce energy consumption and emissions. These measures can be summarised as follows: A. In relation to line design:

- Wide radius curves to reduce rolling resistance. - Tunnels with a generous clearance gauge to reduce additional friction

drag. - Homogeneous speed profile to reduce the energy lost in braking to

decelerate. - Reduced gradients to avoid braking on downgrades. - Reduced distance to reduce rolling and aerodinamic resistance between

the same points of passenger origin and destination. - Use of high electrification voltages and reduction of distance between

substations to reduce ohmic losses. - Installation of reversible substations to return regenerated energy to the

power network. B. In relation to rolling stock:

- Reduction of the mass and rotating masses per seat to reduce rolling resistance and the energy lost in braking.

- Optimization of the aerodynamic coefficient to reduce the aerodynamic drag.

- Reduction of the amount of air that enters the train to minimize intake air resistance

- Increase in the size of the train to obtain reductions in mass and in coefficient C per seat unit.

- Utilization of high-performance traction chains to reduce losses in vehicles

- Low heat transmission coefficients in the bodies to reduce losses in air-conditioning.

C. In relation to operation:


46

- Reduction in the number of train stops to reduce the energy lost in braking.

- Increase in the utilization coefficient to reduce consumption per passenger.

- Implementation of a time margin that allows economical driving. - Implementation of an economical driving system (different according to

whether or not the train has a regenerative brake) which, if possible, can be reprogrammed in real time.

- Reduction of turnover times.

6.2. Best practices applicable to high speed The design and operation measures outlined above are applicable to all kinds of trains. However, some of them are especially applicable to high speed systems, three of which can be highlighted due to their particularly powerful effects at high speeds:

1. Increase of feasible downgrade speeds. 2. Optimization of the train´s exterior dimensions (length, width and height)

to reduce coefficient C per unit of capacity. 3. Reduction of air intake according to actual train occupancy.

6.2.1. Increase of speeds on gradients (downgrades) Trains lose a significant amount of potential energy when they have to brake on downgrades to avoid exceeding the maximum speed. As has been shown previously, this quantity of energy grows as the difference between the actual gradient and what we have called the “gradient of repose” increases. This is due to the fact that the potential energy dissipated on the gradient of repose is used to overcome the rolling resistance, and only when the actual gradient exceeds the gradient of repose must the brake be used. As the “gradient of repose” is that on which the rolling resistance (which increases with speed) equals the gravitational resistance (which increases with the gradient), it can be concluded that the greater the “gradient of repose”, the higher the train’s speed is. And as the loss of energy is greater the lower the “gradient of repose”, it can be concluded that the lower the downhill speed of the train, the greater the loss of energy. This affirmation can be understood intuitively (even by using the experience of driving a car): the slower one has to go downhill, the more one has to brake and, therefore, the more energy is lost. Consequently, a strategy to reduce energy consumption is to increase the downhill speed of the train. This can be achieved with an adequate infrastructure design (which includes large curve radii in downgrade areas) and, once the infrastructure has been constructed, by allowing the train to increase its downhill speed until it reaches the maximum speed permitted by the infrastructure.


47

As the layout of the infrastructure on high speed lines is usually straight or with very wide curves, the advantages of increasing the train’s maximum speed can be found on these lines, whereas on conventional lines the downgrade sections often coincide with curve areas, and therefore the train’s maximum speed is usually greater than the speed permitted by the infrastructure in these areas. Consequently, nothing is gained by increasing the train’s maximum speed. The reduction of energy consumption by increasing the train’s speed was verified on the TGV South-East line in France when, in the 1980s, the speed was increased from 260 to 270 km/h to better utilize the potential energy on the numerous 35 mm/m gradients. This reduction was also verified in Spain by increasing the speed on the Madrid-Barcelona line (with long 25 mm/m gradients, where the maximum speed went up from 280 to 300 km/h). In addition to this direct effect of reducing the energy dissipated in braking, there is another indirect effect derived from running, at least on gradient sections, at a higher maximum speed. In fact, this provides, for the same journey time, a certain time margin which can be used to perform economical driving on horizontal sections, where the driver can opt to coast rather than reduce the train’s speed (if the utilization of the regenerative brake is not high), or to reduce the speed in relation to the maximum (if there is high utilization of the regenerative brake). If it were decided that the time gained by running faster on gradients results in a reduction of the “commercial” journey time, this could indirectly help to reduce emissions in the corridor due to transference of traffic from the plane, thanks to the train being more attractive. The following table shows, by way of example, the effect of increasing the maximum speed of a train (series 102 AVE) on the Madrid-Barcelona line in both running directions.


48

Table 10. Effect of increasing the maxium Speedy of a train (series 102 AVE) on the Madrid-Barcelona line in both running directions

Speed Gradient of repose (mm/km)

Madrid-Barcelona Barcelona-Madrid Energy losts Both directions

(kWh)

Excess height

(mm/km)

Energy lost

(kWh)

Excess height

(mm/km)

Energy lost

(kWh)

200 -6.85 3,479 1,995.3 2,537 1,454.9 3,450.2 210 -7.41 3,299 1,892.2 2,383 1,366.7 3,258.9 220 -7.99 3,118 1,788.3 2,227 1,277.4 3,065.7 230 -8.59 2,940 1,686.3 2,074 1,189.7 2,876.0 240 -9.22 2,760 1,583.2 1,922 1,102.5 2,685.7 250 -9.88 2,579 1,479.5 1,776 1,018.9 2,498.4 260 -10.55 2,403 1,378.6 1,638 939.5 2,318.0 270 -11.25 2,225 1,276.2 1,505 863.4 2,139.6 280 -11.98 2,042 1,171.5 1,371 786.6 1,958.1 290 -12.73 1,861 1,067.7 1,237 709.6 1,777.3 300 -13.50 1,680 963.7 1,107 635.1 1,598.8 310 -14.30 1,500 860.5 981 562.8 1,423.3 320 -15.12 1,326 760.7 855 490.3 1,251.1 330 -15.96 1,164 667.8 740 424.5 1,092.3 340 -16.83 1,007 577.3 630 361.4 938.7 350 -17.73 859 492.9 535 306.7 799.6

At 200 km/h (the speed to which a 6.85 mm/m gradient of repose corresponds), the energy lost in the brake on gradients is 3,450 kWh (around 17% of the total energy imported by the train on the route, including the energy needed for the auxiliary services). If the same train runs at a maximum speed of 350 km/h, the energy lost in the brake on downgrades is reduced to 800 kW/h (around 2,5 %).

6.2.2. Optimization of the train’s exterior dimensions High speed trains can adopt different architectures: concentrated traction or distributed traction; articulated or non-articulated; single-deck or double-deck; wide body or normal body. Also different sizes: From 250 to 1,600 seats. As can be seen in García Álvarez (2010), reducing the consumption of energy per unit of capacity (i.e., per seat) can be achieved by reducing the mass per seat, with a reduction of coefficient C per seat, and with an increase in the train’s capacity (i.e., the number of seats), which in turn affects the “economies of size” consisting of a reduction of the mass per seat and of coefficient C per seat. The same article demonstrates that the elasticity of consumption in relation to the mass per seat is high in commuter services (0.436) and low in high speed services (0.222). However, the elasticity of energy consumption in relation to coefficient C per seat is high is high speed services (0.544) and low in commuter services (0.025). These elasticity values can be seen in the table below.


49

Table 11. Elasticity of energy consumption with varing mass and coefficient C according to type of service ( )Coefor ΔΔΕΔΜΔΕ //

Mass and rotating

masses Coefficient C High speed 0.222 0.544 Conventional long distance 0.414 0.190 Medium distance 0.390 0.072 Commuter 0.436 0.025 Metro 0.668 0.016

The same article also explains how the configurations of articulated and distributed traction trains (even always being beneficial) have more effect on the reduction of mass per seat and, therefore, on commuter services with frequent stops. On the other hand, wider double-deck trains have a greater reduction in coefficient C per seat and, therefore, display their consumption reduction effects with greater efficiency in the field of high speed. A train of the same capacity has a considerably lower coefficient C if it has a wide body or two decks, and even more so if it has both. This is because coefficient C is proportional to the train’s cross-section surface area (its height multiplied by its width) and, to a greater extent, to the train’s “wet surface” area (length multiplied by height times two plus width). Wide-body, double-deck configurations increase the train’s width and height, but, capacity being equal, allow more than proportional reductions of the length, the combined effect being to significantly reduce coefficient C per seat. It can be estimated that the energy consumption of a wide-body, double-deck train with 350 seats is 38% less than that of an equivalent normal-body, single-deck train, since although the former is half a metre wider and higher, its length is reduced from 200 to 90 metres. In addition to this, on lines with short platforms or heavy traffic density, wide-body and/or double-deck configurations allow, for the same platform length, the train’s capacity to be increased, thereby producing two effects in terms of the reduction of coefficient C per seat: one deriving from the smaller dimensions for the same capacity, and the other from the greater capacity.

6.2.3. Air intake reduction Moving trains devour a considerable quantity of air, around 10 cubic metres (12 kilograms) per person and per hour. This has two disadvantages from the energy point of view:

• The ambient temperature and humidity of the air that enters the train has to be changed in order to meet the train’s air-conditioning requirements (temperature, humidity). The more extreme the outside temperature and, logically, the greater the quantity of air, the more the amount of energy required will be. This effect is obviously independent of speed.

• Another effect deriving from air intake is a consequence of the fact that the air that enters was initially still and must be accelerated almost instantaneously up to the train’s speed, which produces a retarding force in the vehicle and, therefore, an increase in energy consumption. This additional energy depends linearly on the train’s speed (which is why it


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important in high speed systems) and on the air density (therefore it is higher with cold temperatures), and it can represent up to 4% of the total energy consumption of a high speed train.

Therefore, reducing the quantity of air that enters the train has an immediate effect on the reduction of energy consumption, and this is especially appreciable at high speeds.

Do the seats or the passengers need the fresh air? International standards specify a quantity of refreshed air per person and hour (between 5 and 15 cubic metres), but as the air refreshing system does not take train occupancy into account, in order to ensure compliance with the standard, in practice the air is refreshed by introducing the specified volume of air for each seat instead of for each passenger. If the train is equipped with systems that regulate air intake according to the actual occupancy of each car, a reduction in consumption proportional to the percentage of empty seats could be achieved. For example, for the typical utilization of 0.65, consumption could be reduced by 35%. Intelligent air intake management systems could be used on high speed trains not only to reduce energy consumption, but also to improve their performances. In fact, on a long upgrade the amount of refreshed air could be reduced, allowing the train to have additional power for traction, whereas on the subsequent downgrade the quantity of intake air could be increased, thus compensating for the previous lack of air and permitting an additional brake. Carbon dioxide and air quality detection systems inside the cars (together with the appropriate software) could help to improve air intake management and, consequently, to optimize energy consumption.

Around 5.5% energy reduction In the specific case of a direct high-speed train from Madrid to Barcelona (Talgo class 102), the imported energy consumption in the pantograph is 15.53 kWh/km, with the net amount being 14.59 kWh/km. Of this energy, 1.88 kWh/km corresponds to additional drag due to air entering the train (12.87% of net consumption), and it can also be estimated that 0.4 kWh/km (2.74% of net consumption) corresponds to conditioning this mass of air. So, a 35% reduction in the amount of air entering the train means a reduction of 0.657+0.140 = 0.8 kWh/km, i.e. a 5.46% reduction of net energy consumption. This reduction must be achieved with independent systems in each car that, according to the programming established, regulate air intake depending on the number of passengers, not the seats on the train.


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7. Bibliography ALCOL, A. (2004): “Resistencia al avance y aerodinámica de trenes”, UPCO, Apuntes Master de Sistemas Ferroviarios ICAI.

ALONSO, J. M. (2004): “Conceptos aerodinámicos sobre el movimiento de los trenes”. Letter to the author dated 7 June 2004.

ANDERSON, E. and LUKASZEWICZ, P. (2006): “Energy consumption and related air pollution for Scandinavian electric passenger trains”, Report KTH/AVE 2006:46, Stockholm (Sweden).

ARAGÓN GURRÍA. E. (2005): “Determinación de las condiciones óptimas de conducción como forma de reducir el consumo energético de los trenes”, final-year Industrial Engineering Project directed by Alberto Garcia Alvarez. ICAI, June 2005.

BARRÓN DE ANGOITI, I. (2007): “Introducción a la alta velocidad ferroviaria”. Apuntes del Master de Sistemas Ferroviarios ICAI, 6th edition.

BERNHARD, M. and GUIEU, M. (1976): «Mesures récentes de la résistance a l´avancement de matériels roulants », in Revue Générale des Chemins de Fer, April 1976 issue, París.

GARCÍA ÁLVAREZ, A. (2004): « Dinámica de los trenes en alta velocidad », published by Fundación de los Ferrocarriles Españoles.

GARCÍA ÁLVAREZ, A. (2005): “El tren de alta velocidad no es un depredador de energía”, in Dyna, June 2005, LXXX-5, pg. 33 to 38; edition updated in May 2007.

GARCIA ALVAREZ, A. (2006): “Incidencia del tren de alta velocidad en el consumo energético y emisiones del sector transporte”; speech given in Madrid on 17 November 2006 during the 6th Science Week (VI Semana de la Ciencia) (downloadable at www.ffe.es>estudios y programas>publicaciones electrónicas).

GARCÍA ÁLVAREZ, A. (2007). Consumo de energía y emisiones del tren de alta velocidad en comparación con otros modos de transporte. Anales de mecánica y electricidad.

GARCÍA ÁLVAREZ, A. (2007a): “Normalización de los consumos energéticos de los trenes de viajeros”, paper presented at the 3rd Railway Innovation Conference (III Congreso de Innovación Ferroviaria) (Tenerife, May 2007)

GARCIA ALVAREZ, A. (2007b): “Consumo de energía y emisiones del tren de alta velocidad en comparación con otros modos”, in “Anales de Mecánica y Electricidad” (ICAI Engineers Association Magazine), Vol. LXXXIV, Fas. V, Sep.-Oct. 2007); and expanded, with the same title, in “Via Libre” (issue 515, January 2008).

GARCIA ÁLVAREZ, A. and FERNÁNDEZ GONZÁLEZ, E. (2008): “Recorridos y cociente entre trayectoria y desplazamiento en el transporte por ferrocarril”; Notas técnicas Enertrans/9; January 2008, published by Fundación de los Ferrocarriles Españoles.

KEMP, R.J. (1993): “The European High Speed Network”, in “Passenger Transport after 2000 AD”; published by Feilden, Wickens and Yates.

KEMP, R. (2004): “Take the car and save the planet. Thought trains were always greener than cars? Think again”, IEE Power Engineer, October-November 2004.

LUKASZEWICZ, P. (2001): “Energy consumption and running time for trains” (Doctoral Thesis). Railway Technology, Department of Vehicle Engineering, Royal Institute of Technology, Stockholm.

INTERNATIONAL UNION OF RAILWAYS (UIC)16 rue Jean Rey - F-75015 PARISTel: +33 (0)1 44 49 20 20Fax: +33 (0)1 44 49 20 29

PASSENGER DEPARTMENT - HIGH SPEED ACTIVITYLegal deposit: December 2010ISBN: 978-2-7461-1965-9www.uic.org

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High speed, energy consumption and emissions

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