TRAFFIC AND TRANSPORTATION - 2.pdf

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L E C T U R E - 2

TRAFFIC AND

TRANSPORTATION

SURYA SCHOOL OF ARCHITECTURE



Traffic Capacity of Roads

The traffic carrying capacity of any road primarily depends on the following factors:-

Characteristics of road such as gradients, number of lanes, visibility, cross-traffic, pedestrian’s movement, etc.; and

Characteristics of traffic such as speed of vehicles, type of vehicles, driving habits of road-users, etc.

To arrive at the theoretical maximum capacity of road per lane width, the following assumptions are made:-

All vehicles on road are of uniform length.

All vehicles on road are running at uniform speeds.

The distance between successive vehicles is uniform.

The average capacity of a normal lane varies from 700 to 2000 vehicles per hour. In practice, it is found that when capacity oflane increases to 1000 vehicles per hour, it leads to discomfort, congestion, more chances of road accidents and

inconvenience in driving.

The width of traffic lane is determined by the following equation:

The clearance will depend upon the speeds of the vehicles. The faster the traffic, the greater the clearance and vice-versa.

The number of lanes will be decided from the volume of traffic. The suggested number of lanes for different traffic capacities areas follows:-

• 4 lanes 2 in 1 direction ………………..600 vehicles per hour per lane



At curvatures and for providing parking facilities, extra lanes may be provided as required.


Width of traffic lane = width of the largest vehicle + clearance



Traffic Management

It is defined as the means and methods adopted to utilize the road systems of a town to the maximum possible extent so as togrant convenience, comfort and safety.

Traffic management is a science by itself and it includes the study of:-

Regulations for traffic

Controlling and guiding measures for traffic

Flow of traffic at junctions

Parking areas

Traffic survey

Engineering elements of road system affecting traffic operation Improvement of traffic facilities in existing towns, etc.

A well planned town is faced with minimum traffic problems. Hence, while planning for a new town, enough care should betaken to see that no traffic problems of any magnitude will arise in the future. In a similar way, the roads of existing townsshould be re-laid and realigned so as to solve some of the acute traffic problems of that town.

OBJECTIVES OF TRAFFIC MANAGEMENT:

Following are the main objectives of traffic management:-

To achieve smooth and easy flow of traffic at intersections;

To develop the methods of improvement in general and for solving specific problems in particular;

To have safe, convenient, rapid and economic transport of persons and goods;

To improve the speed of vehicles;

To increase traffic carrying capacity of roads;

To make the streets safe for the movement of both, pedestrians and vehicles;

To reduce the delays in road journeys;

To reduce the chances of road accidents to a minimum;

To remove traffic congestion; etc.




Traffic surveys

It is necessary to collect the necessary data in connection with the traffic to be carried by the road system of the town.For this purpose, the traffic counts are carried out. The procedure adopted and the information collected are as follows:-

A typical proforma to be filled up during the traffic survey is framed. It contains columns such as variations of traffic,volume of traffic, speed of vehicles, type of vehicles, maximum wheel loads, goods conveyed and origin and destination oftraffic.

The numbers of convenient and representative points are selected along the road.

The traffic counts are carried out at these points, usually once or twice or more a year depending upon the importance ofthe road.

Each traffic count is extended for a reasonably long period, usually a week and during this period, the count is takencontinuously i.e., for 24 hours of the day.

For more important roads, the separate traffic counts are made for the up and down traffic.

In addition to the above procedure, the additional information is also collected during the traffic survey work, such as:-

location and nature of street accidents;

volume, nature and extent of parking;

public parking facilities;

routes followed by public vehicles;

volume and variations of pedestrian traffic;

conditions of road surfaces;

existing traffic rules and regulations etc.

The proforma of traffic count should be carefully filled up and no item should go

unattended. The data obtained from the traffic survey should be properly studied

and analyzed before recommending measures of improvements for the road under

consideration.




Traffic surveys

TRAFFIC VOLUME STUDY: Traffic volume studies are conducted to determine the volume of traffic moving on the roads andclassifications of roadway vehicles at a particular section during a particular time. It represents the number of each type ofvehicle crossing a traffic station.

Objectives: The purposes of carrying out traffic volume count are designing, improving traffic system, planning, management etc.

Design purposes

a) Structural and geometric design of pavements, bridge, and other highway facilities. Structural design is based on repetition ofwheel load on the pavement in entire design life. AADT is needed with traffic growth rate to compute design wheel repetition.Geometric design is based on peak hour volume to avoid congestion.

b) Intersection design including minimum turning path, channelization, flaring, traffic control devices viz. traffic signs, markings,

signals based on approach volume and turning proportions.c) Pedestrian volume study is useful for designing side walks, pedestrian crossing etc.

Improvement purposes

a) To allocate limited maintenance budget rationally, it is important to know the traffic volume carried by a particular roadwaysection in order to decide the importance of the road and fixing its relative priority.

b) In order to improve the roadway operating condition, it is important to know the traffic volume.

c) To examine the existing operating/service condition of a roadway section.

d) To check the need (warrant) traffic control devices.

e) To determine the type of improvement measure need to be taken.f) To measure the effectiveness of a traffic control measure

Planning Purposes

a) Accurate information on the amount of traffic on the roads is vital for the planning of both road maintenance and improvementpolicies

b) Traffic volume network analysis helps in deciding/planning if there is need for

c) Improvement

d) Expansion in terms of construction missing links, by-pass, alternative road etc.




Traffic surveys

Dynamic Traffic Management Purposesa) Up to date and continuous flow/congestion information is essential for optimizing

b) Traffic signal design and thereby improving junction performance

c) Network productivity by providing information to the road user

Other Purposes

a) Estimation of highway usage

b) Measurement of current demand of a facility

c) Estimation of trendsd) Economic feasibility evaluation

e) Computation of accident rates- accidents/100M vehicle-miles

1. Annual Average Daily Volume of Traffic (ADT): It represents the average of 365 days. For finding ADT, 24 hour counts are

made at five or fifteen mintues’ intervals. Traffic census stations are installed and a day is chosen to find the ADT. This helps in

planning of major roads.

2. Seasonal Average Daily Traffic: At places like business, commercial or residential centers, traffic surveys are conducted to find

out the maximum volume of seasonal traffic. This helps in planning of roads to serve that particular center.3. Hourly Average Traffic Volumes: Traffic census is conducted on peak hours of the day in different months to determine the

maximum average traffic volume per hour. It helps in the planning of traffic lanes of particular roads.

4. Pedestrian Volumes: The volume of pedestrian traffic is found out which helps determine the width of footpaths, pedestrian

crossings, etc.

5. Classified Traffic Volumes: Here, the intensity or the number of vehicles of different categories of determined, such as bullock-

drawn carts, tongas, cycles, rickshaws, cars, buses, trucks, etc. For this either manual counting or automatic reading is

resorted to. This helps in fixing up the geometric as well as structural design of roads.


Electronic Counting Board Mechanical Counting Board



Traffic surveys

1. Origin – Destination Studies (O and D surveys): The study is made for origin and destination of passengers and goods

traffic , mode of travel of people, i.e. on foot, or by cycles, buses, cars, their direction, time taken, purpose of travel and

halts made in the travel by them. It helps to provide speedy transport, necessary thoroughfares to fix the routes for

different traffic to avoid congestion and to specify one way traffic where needed.

Methods of O and D surveys are as follows:-

Roadside interview method – The drivers and persons are contacted to know their origin and destination, past, present

and future trips to be carried out.

Parking Method – The drivers of parking vehicles are contacted to collect similar information about their origin and

destination, past, present and future trips to be carried out.

License Plate Method – Here the registration number of the vehicles, time of entering or leaving the area under survey

are recorded.

Return post card method – Here the pre-paid blank post cards with return address are distributed to drivers of vehicles

with a request to fill the questionnaire and to return it duly completed by mail. This method is adopted where traffic is

heavy.

Tag on card method – Here the pre-coded cards are tied on the vehicles when they enter the area under survey. When

the vehicles leave and reach the cordon area, the tags are removed and the time, destination, route of travel are recorded

on the tags. This method is adopted where the traffic is heavy.

Home interview method – The drivers and vehicle owners are contacted in their homes and necessary information is

collected.

Workspot interview method – Here the necessary information is collected by personal interviews at the workplaces, like

offices, factories, etc.

The Statistics so collected in O and D surveys can be represented in the form of maps, charts, etc., and used for

recommending the measures of improvement for roads under construction.




Traffic surveys

CHIEF USES OF THE TRAFFIC SURVEYS: It becomes possible to suggest suitable remedies for proper functioning of the road.

It enables a town planner to prepare town planning schemes capable of meeting traffic requirements.

The details collected in traffic surveys are used to decide the location of signals and other controlling devices on the road .

The economic costs of construction and maintenance of the road can be worked out with reasonable accuracy.

The selection of proper type of surface can be made from the study of results of the traffic surveys.

The statistics collected during the traffic surveys can be exhibited in the form of maps, charts and tables.

The width, thickness, gradient and alignment of road can be appropriately designed to meet with the expected traffic

volume.

THE MAIN PROBLEMS ENCOUNTERED IN TRAFFIC SURVEYS

Comparability between surveys. It is usually very important to compare survey results over time. This is frequently very

difficult because of different sample sizes, different questions, different response rates, and different geographical collection

units. These are usually major problems for studies trying to compare the results from different agencies.

Non response bias. There are significant variations in the response rates achieved by surveys. The larger the non response

rate, the less reliable will be the results. A 60% response rate is sometimes considered as a threshold. Many surveys fail to

achieve high rates of response, for example the 2001 NHTS survey only achieved 41%.

Coverage bias. The survey instruments frequently contain hidden biases. For example automatic telephone surveys

exclude cell phone users and those without a land line connection.

Un-reporting of trips. Research is now showing that surveys and travel diaries may be undercounting trips made. Some test

surveys are using GPS devices to record trips and indicate that in the Kansas City survey 10% of trips were unreported and

in the case of Laredo the figure was as high as 60%.




Traffic Congestion

In urban areas, there is a heavy rush of vehicles and pedestrians during peak hours ofthe day and it results into overcrowding of road. Such a condition is referred to asthe TRAFFIC CONGESTION and it is developed mainly due to the followingcauses:-

The factors such as faulty intersections, narrowness of roads, steep curves andgradients, poor condition of vehicles using the road, etc. also contribute tooccurrence of traffic congestion.

The haphazard parking of vehicles and physical encroachments on the road arenot handled severely.

The movements of vehicles are allowed in the conflicting directions.

There is absence of civic sense and strict enforcement of the traffic rules andregulations is not carried out.

The streets originally planned for a single use are occupied by the slow- movingand fast-moving automobiles, cyclists and pedestrians.

The roads are not owned by individuals and as such, the transportation by road is aform of public utility service. The proper functioning of road network depends onthe co-operation of public using the road system. In the transportation system, thepeople responsible for traffic congestion can be grouped in the following threecategories:-

General public: It is treated as a passive element, but sometimes becomes amajor source of certain nuisances to the transportation management.

Road users: This is in the form of vehicular traffic and trips are made by theowners of vehicles by any suitable mode of traffic.

Transport personnel: The planning, design, operation and management oftransportation system are carried out by persons who have expert knowledge ofthe system.

It is significant to note that every individual falls in all the above three groups at onetime or other, but strangely behaves indifferently in different capacities at differenttimes.


Congestion on a city road in Moscow.

Congestion on a city road in U.S.A.

http://en.wikipedia.org/wiki/File:Moscow_traffic_congestion.JPG



Traffic Congestion

THE DISADVANTAGES OF TRAFFIC CONGESTION:

1. It makes the surrounding area polluted with undesirable gases, vapours and odours.

2. The chances of road accidents are increased.

3. The driving through traffic congestion area becomes very tedious and it adversely affects on the health of drivers of thevehicles.

4. There is more wear and tear on vehicle and the persons have to spend considerable time sitting idle during traffic jamswhich they might have more productively spent somewhere else. Thus, the road congestion involves and economic lossalso.

5. Traffic congestion delays urban people in going to places of work. It increases cost of living.

6. There is natural wastage of petrol and gasoline used for running automobiles because the automobiles do not attain the

optimum speeds for which they are designed.7. All the streets have become highways full of noise, bustle of the vehicles.

REMEDIES FOR TRAFFIC CONGESTION:

1. Accommodating bus-stops of public vehicles at suitable places along the road;

2. Adopting means to segregate the traffic of the various categories;

3. Adopting the system of staggered working hours so as to have better matching of street capacity with traffic volumesgenerated by employment centres;

4. Arranging educational methods like lectures, films, video cassates, slide shows, T.V. programmes, etc. to develop public

opinion to abide by traffic rules and regulations;5. Controlling the movements of vehicles by making one-way schemes;

6. Enforcing strictly the traffic rules and punishing the defaulters;

7. Fixing time and area for movement of certain types of fast-moving and slow-moving vehicles;

8. Prohibiting parking on one side or even both sides of the road;

9. Prohibiting U-turn movements on the major roads;

10. Restricting loading and unloading of the goods;

11. Requiring pedestrians to cross major streets at specified locations, designated and demarcated for such purpose; etc.




Traffic Control

The objects of having effective traffic controlling devices are as follows:- To develop free and rapid flow of traffic on the roads and streets in towns; and

To prevent the rapid traffic flow from being in undue danger either to its own units or to the public at large.

Traffic control is achieved either by means of constructive measures or restrictive measures.

1. The constructive measures include design of junctions, number of traffic lanes, layout of curves, etc. and they are looked

after by the town planners and road engineers. The ultimate aim of the constructive measures is to make the roads as safe

for movement as the railways.

2. The restrictive measures include traffic rules and regulations, traffic signs and signals, etc. and these measures are

enforced by the police department of the government. The ultimate aim of the restrictive measures is to maintain publicsafety until such time as the roads have been made structurally safe and adequate.

The various methods of traffic control adopted in practice can be enlisted as follows:-

1. Achieving segregation or separation of traffic of conflicting nature like slow and fast, local and through, etc.

2. Imposing heavy penalties on the defaulters of traffic rules and regulations;

3. Imposing street restrictions as in case of the road over a bridge;

4. Installing devices consisting of signs, signals and markings placed on or adjacent to a street or a road for the purpose ofregulating, warning or guiding the traffic;

5. Making proper design of junctions i.e., providing them with traffic islands, roundabouts, subways or bridges;

6. Making the street one-way;

7. Providing good visibility, easy curves, sufficient widths and parking places;

8. Regulating turning of vehicles at junctions manually by policemen; etc.




Traffic Segregation

PRINCIPLES OF TRAFFIC SEGREGATION The main cause of frequency of road accidents is the inter

mixture of traffic, slow and fast, local and through. The

solution is the segregation or separation of traffic either on

separate tracks on the same road or entirely on different

roads.

The two ways of segregation of traffic are:-

Place Segregation: Segregation of tracks on the same road.

1. Grade Separation - Keeping the track on different levels one

at a higher and one at lower level.

2. Constructive Measures - Keeping the tracks on the same

level but separation is caused by a physical obstruction,

such as raised islands, footpaths, fencing, or color bands.


Grade Separation

Constructive measures adopted for traffic segregation – raised island, footpaths, etc.



Traffic Segregation

Time Segregation: As per this type, traffic is allowed to pass at different timing or intervals, as such traffic in one directionis entirely stopped, for a short time while the cross traffic is allows to pass on and vice-versa. This is done generally by

automatic traffic signals by colored lights. The timing, phasing and installation of signals have to be determined by

conducting a detailed traffic survey. These come under Restrictive Measures.


Traffic Signals



Road Junctions

Junction or intersection may be described as a road situation where two or more roads meet or cross one another at the sameor different elevations.

The design of road junctions should be done carefully to make it more safe for movement of the vehicular traffic andpedestrians. Accidents generally occur at road junctions and hence, proper precautions should be taken in their design.They should be properly signaled and it is essential to have proper segregation and control of traffic. There are a numberof types of road junctions to be designed for different conditions of traffic.

The factors that govern the type of road junctions

are as follows:-

Volume and type of traffic

Number of intersecting roads

Availability of traffic control devices

Degree of traffic congestion

Funds available

The basic consideration in the design and operation

of intersections must be the capabilities and limitations

of the drivers, pedestrians and vehicles using the

facility. A confused driver is an unsafe driver. Hence,

the intersection design must be predicted upon what

the driver will do rather than what he should do. The

adoption of this principle will be facilitated, if sound

traffic operation procedures are inherent in all phases

of the design process.




Road Junctions

PRINCIPLES OBSERVED IN DESIGN OF ROAD JUNCTIONS:

Angle of crossing: Acute angle crossings should be avoided.

The subsidiary roads should be made to meet at right angles

to the main road as far as possible.

Camber: As far as possible, the whole area of the road junction

should be made in one level.

Channelizing: Road junctions should be properly channelized,

i.e. the number of points of conflict of traffic are minimized and

lines of flow of traffic are made to cross at right angles or nearly

at right angles. A properly channelized road junction permits

right actions to do smoothly and makes wrong actions difficult.

Entry Speeds: The design of road junctions should be

ingeniously done such that it does not halt the main road traffic but only allow to show down the high entry speed to avoidaccidents.

Gradients: Change of gradient at road junctions should be avoided.

Importance of Road: If road junction is meant for major roads and local roads, the latter should be carries under or over

the former by subways or bridges respectively. Kerbs (Curbs): To demarcate the boundary between a road and footpath, kerbs are provided.

They should be of proper height and visible at night.

Pedestrian Traffic: For road junctions having heavy pedestrian traffic, hand rails should be

provided adjacent to kerbs with openings at pedestrian crossings.

Simplicity: Road junctions should be simple. The routes for traffic should be clearly defined.

Visibility: At junctions, there should be clear view across corners from sufficient distance so as

to avoid collision of vehicles approaching from other directions.


Channelization techniques



Road Junctions

TRAFFIC ISLANDS:The space at a road junction over which traffic is not allowed to

move is known as a traffic island.

The arrangement of traffic islands at the road junctions serves

the following objectives:

The efficiency of traffic handling is increased.

Segregation of traffic into proper channels as they serve

as guides to drivers in negotiating junctions. They serve as shelter for pedestrians crossing roads.

Thus, they are also referred to as Refuge Islands (R.I.) or

Safety Islands.

The vehicles are compelled to move in one direction only

and separate strips (alternating in black and white) across

the roads are provided for crossing of pedestrians. Thus,

the chances of accidents are reduced.

They provide proper place for installation of traffic signsand other controlling devices.

Traffic islands should be constructed 200 mm higher than the

road level. They are sometimes provided with lawn, statue

or fountain to make them distinct and attractive. They

should be painted with color which contrasts with the color

of road pavement.


Refuge Islands, Central Median

Pedestrian Crossing



Road Junctions

This type of road junction is formed when a local road

meets with other local or main road at right angles.

This is the simplest form of junction and provides adequate

sight distances and radius kerbs.

A traffic island can be provided that ensures that the traffic

on local road approaches the main road at a lower

speed.

This type of road junction is formed when one road meets

the other at an acute angle.

If there is no traffic control is provided, these junctions proveto be very dangerous, especially if road are main

roads. Thus, necessary traffic segregation in the form

of traffic islands, etc. should be provided.


T- Junctions

Y- Junctions



Road Junctions

This type of road junction is formed when two roads cross

each other at acute angles.

These junctions do not provide sufficient sight distances

and therefore should be avoided as they prove to be

grave hazards to traffic.

This junction is formed when two roads cross each other

at right angles at different places.It is necessary that the staggered roads should be of

sufficient distance apart or atleast 100 m apart so as

to admit the crossing traffic to weave freely across

the path of the opposite traffic flow.


Acute-angled Junctions

Left Staggered Junction Right Staggered Junction

Staggered Junctions



Road Junctions

This type of road junction is formed when two roads cross each other at right angles.

In this type the traffic moving in opposite direction has to make a complete right angled

turn. Where space is available the traffic is controlled by creating in the centre of the

junction a dead area called a traffic island or roundabout or rotary around which the

traffic is compelled to go clock-wise in gyratory manner, always keeping a left hand

rule, so as to avoid chances of accidents due to short cuts. The movement of traffic

in the opposite direction is altogether eliminated.


Right - angled Junctions



Road Junctions

Design factors of a roundabout:- Design speed: The vehicles approaching the rotary slow

down but do not stop to allow the cross-traffic to pass. The

speed of traffic is taken as 40 kmph and 30 kmph at rotaries

in rural and urban areas respectively.

Radii of entrance and exit curves: For designed speed of 40

kmph , the radius of entry curves is 20 to 35 m and for 30

kmph is 15 to 25 m. the radii fo rexit curves should be one

half or twice the radius of entry curves. Rotary Island: The shape of the central traffic island may be

circular, rhombus or diamond. Its size largely depends on

the volume of traffic. The radius of central island should be

1.33 times the radius of entry curves. Island should be

fenced by stone kerbs. It may be made pleasing with some

landscaping and water features. However, good visibility

should be kept open as far as possible.

Width of Carriage-way: The width of carriageway around the

rotary should be kept slightly more than average width ofcrossing roads.

Pedestrian Traffic: The pedestrian crossing should be

provided at appropriate places with a refuge island. In case

of large pedestrian traffic, it should be controlled by human

control or automatic signals to regulate the movement of

pedestrians. The other provision of crossing facilities is

provided in the form of subways and over-bridges.


Subway and Over-bridge for pedestrian crossing

Roundabout design features



Road Junctions


Circular Pedestrian Bridge at Lujiazui, China

The walkaway is 5.5 meter high and can fit 15 people walking side by side.



Road Junctions


Mini Roundabout Single lane Roundabout Multi- lane Roundabout

Tangential Roundabout Circular Roundabout Double Roundabout



Road Junctions

ADVANTAGES OF ROUNDABOUTS: Provides a simple solution for road junction where more than four roads meet.

There is little loss in traffic capacity as there is continuous flow of traffic through the roundabout. A well-designed

roundabout can accommodate a total traffic of 3000 cars per hour and it also enables radial streets to carry traffic to their

full capacity.

There is smooth and orderly flow of traffic with li ttle delay.

The vehicles as they approach the roundabout are merging and weaving in the traffic stream. It thus provides a high

degree of safety and hence, there are less chances for serious collisions or accidents.

The wear and tear of vehicles using the roundabout are reduced as stopping and starting of vehicles are less frequent.

The maintenance cost is considerably reduced due to the fact that the roundabout can e made a self -controlled traffic

intersection avoiding the necessity of traffic police or signals.

DISADVANTAGES OF ROUNDABOUTS:

If traffic is to be stopped from time to time for crossing of pedestrians, the orderly movement of traffic is seriously upset.

Hence, the roundabouts are sometimes elevated and subways are provided for pedestrians to pass for all the time.

It becomes congested and hazardous under fog conditions.

It may confuse the drivers who are not familiar with such types of construction.

It requires large area of flat land and hence, it cannot be adopted where land values are high.

It requires the installation of complicated traffic signs, having heavy mixed traffic and large number of cyclists, pedestrians

and animal drawn vehicles.

It proves to be unsuitable for high speed roads.




Road Junctions

This type of road junction is formed when more

than two roads cross each other.

They are highly undesirable and dangerous if not

properly designed.

Provision of a large rotary in the centre will

separate the traffic, therefore, avoiding

congestion.


Grade Separators

Multiple Junctions

A grade separation is the arrangement of taking one road over or under theother by means of a bridge. It is also known as a flyover junction. Thereis no physical connection between the separated roadways.

The term interchange is used to indicate a grade separation having facility for

traffic to pass from one intersecting road to the other. Thus, theconnecting roads known as ramps or turning roadways are provided toenable limited or full movements between the separated roads at aninterchange. Following are the four common types of interchanges:

• Clover-leaf crossing

• Diamond crossing

• Rotary interchange

• Three-way interchange



Road Junctions




Road Junctions

DIAMOND INTERCHANGE

It is the simplest form of interchange. The arterial road used

for fast moving traffic is taken over the bridge at the

centre whereas the local road carrying slow traffic goes

underneath through the bridge. There are only left

turns and no right turns, hence there is no chance of

collision.


Y-TYPE INTERCHANGE

The shape of the interchange resembles the –

letter and hence the name. It comes under

three leg interchange.



Road Junctions

THREE WAY INTERCHANGE

Utilized in locations where there are only

three approaches to the interchange.

The arrangement with a simple bridge is

known as trumpet and is also referred to

as T-Intersection.


CLOVER LEAF INTERCHANGE

It is an improved type of diamond crossing. It was first usedin America.it is the most effective means of traffic

control as all conflicting flows of traffic are avoided.The through traffic coves at its own speed. It is

therefore superior to a roundabout as there is noweaving and slowing down of traffic.

It is best suited for intersections carrying equal amounts of

traffic in all four direction.

TRAFFIC AND TRANSPORTATION - 2.pdf

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