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Context Defining the problem Sources of information Source – pathway – receptor Conclusions
Content
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Pressure to enhance motorway network by increasing capacity
Some schemes are unable to proceed because of their implications for air quality and compliance with limit values, chiefly NO2.
In the absence of any control over the vehicle types using the motorway, what are the alternative means of reducing air quality impacts?
Context
Clear Air Thinking 4
Defining the problem
M25, Essex70 mph speed cars, 60 mph HGVs
2013 EFT
100.000 veh/day
Clear Air Thinking 6
Consult with: Government departments, local government, government agencies, academics and European research organisations.
Search scientific and grey literature, eg the Dutch Innovatieprogramma Luchtwaliteit or IPL
Analyse and evaluate findings Produce a draft report
What we did
Clear Air Thinking 7
Purchase properties? Not viable for a number of legal and ethical reasons
Modify properties? eg forced ventilation. Technically dubious and legally suspect. See planning inquiry decision on student accommodation near Blackwall Tunnel.)
Conclusion: little or no scope to solve problem by intervention at receptors.
Receptors
Clear Air Thinking 8
Pathway modifications through: Barriers Enclosure in tunnels Pollutant removal by catalytic surfaces
Pathway
Clear Air Thinking 10
Barriers – CFD modelling
Barrier No barrier
Notes: US EPA research
Bowker et al 2007
Birds eye view of a section of Interstate -440 in Raleigh, N Carolina
Complements field study
QUIC CFD model
Clear Air Thinking 12
Barriers – influence of buildings and trees
Observation:
The influence of obstacles behind the barrier dilutes its beneficial effect, in respect of pollutant concentrations
Clear Air Thinking 13
Barriers – experimental data
Data from Dutch IPLField experiments at A28 siteMeasurements made of NOx, NO2
and PM10 over several months4m and 7 m noise barriers
Clear Air Thinking 16
Catalytic surfaces using TiO2 for promoting oxidation to soluble nitrate.
Theoretical – no practical experimental evidence to support this technique in real world conditions.
Trials by HA alongside the M60 and also as part of the Dutch IPL.
Fails because of insufficient surface area, insufficient UV light, damp surfaces and insufficient pollutant contact with coated surface. 1% reduction at best.
Pollutant removal
Clear Air Thinking 18
A largely theoretical concept Investigated as part of the Dutch IPL Would almost eliminate motorway as a pollution
source along its length – although would concentrate pollution at tunnel portals.
Dutch IPL quotes costs of €6M -€65M per kilometre Passive pollutant removal possible through
catalytic coatings or pollutants dispersed as an elevated source through roof vents.
Enclosures -feasibility
Clear Air Thinking 19
The Melbourne ‘Sound Tube’
Real world example built as a noise barrier
Melbourne CityLink urban freeway
300m long and costing AU$ 5 M
No reported data on air quality implications
Clear Air Thinking 20
Influences on emissions: Traffic volumes Traffic composition, eg %age Euro VI/6 vehicles Flow state, ie free flow or congested
Emissions – speed reduction
Clear Air Thinking 21
The most directly useful experience is that of Dutch urban motorways in the period 2002-2009.
80 kph speed limits imposed on 10 sections of motorway. Previous limits either 100 or 120 kph.
Extensive roadside measurements made of air pollutants, especially in Amsterdam. Coupled with dynamic emission simulation modelling (VISSIM).
Speed limit reduction – the evidence
Clear Air Thinking 22
Speed limit trial results (Kalter et al 2005)
Location NOx emission
reduction
NOx
concentration decrease (road contribution)
NO2
concentration decrease (absolute)
A10 West 17% 12-20% 3-6%
A20 Rotterdam 9% 7-9% 1-3%
A13 Overschie 13% 10-14% 4-6%
A16 Dordrecht 8% 4-7% 0.5-2%
A12 Voorburg 11% 7-10% 2-3%
A9 Badhoeveddorp 19% 10-14% 1-2%
A12 Utrecht 17% 14-16% 4-5%
A2 Waardenburg 19% 10-16% 4-6%
A16 Rotterdam 9% 7-9% 1-2%
A4/A12 -zuid 15% 10-20% 3-5%
Clear Air Thinking 23
The contribution of HGVs is important and influential in the outcome.
Positive outcomes arise through smoothing of flows.
Biggest improvements arise in PM concentrations, not NO2.
This intervention is politically charged and polarising.
The Dutch experience with speed limits – lessons learnt
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No easy solutions, but the HA is still committed to exploring options.
Effectiveness of the obvious interventions is limited – except for theoretical and expensive solutions such as enclosures or canopies.
Reducing emissions at source is ultimately the best solution – and will occur in time with the penetration of EuroVI/6 vehicles and the uptake of ultra low emission vehicles.
Closing thoughts
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