Greener Journeys has published new research which demonstrates that reducing congestion must be at the heart of Government's strategy to improve air quality. Halving average city traffic speeds leads to a 50% increase in NOx emissions. While it is essential to clean up diesel vehicles, it is also crucial that the continual decline in urban traffic speeds is tackled.
Traffic congestion in the UK's largest cities is 14% worse than it was five years ago, and in the last year alone has deteriorated by 4%. Falling traffic speeds drastically worsen air quality. Morning peak traffic speeds in central London have fallen from 10mph in 2006 to 7.5mph in 2016, causing a 10% increase in NOx from diesel cars and vans, and a 25% and 27% increase for buses and trucks.
Improvements to traffic flow can yield huge reductions in NOx emissions across all vehicle types, but for buses the results are particularly impressive. For Euro VI diesel buses, which will be compliant in CAZs, NOx emissions are more than halved by increasing speeds from just 3.7mph to 5mph.
Whilst Government has recognised the need to improve traffic flows, its proposed solutions of removing speed humps and traffic light sequencing will not address the root of the problem. 75% of traffic congestion is caused by excess traffic. Congestion will only be solved by reducing the number of vehicles on the road, and this will require demand management and some measure of car restraint.
A huge concerted effort will be needed if NOx levels in our towns and cities are to be brought to safe levels.
Government's new Air Quality Plan says that without further action, over 70% (31 out of all 43) of the UK zones will still not be compliant in 2020, largely because "real world" emissions from Euro 6 cars, and Euro 5 and Euro 6 light goods vehicles, are all higher than expected.
However, there are serious contradictions in the new plan. Government has said local authorities should only introduce charging Clean Air Zones (CAZs) if they are unable to identify "equally effective alternatives" for bringing NOx levels down to within the European limit values. But the technical report makes clear that only charging CAZs are expected to achieve the compliance of zones in the shortest time possible.
Not only has Government been very cagey about which areas will need to become charging CAZs, but it has also soft-peddled on the issue of diesel cars.
Diesel cars are the single biggest contributor to NOx levels, responsible for 41% of all NOx emissions from road transport. However, Government's CAZ hierarchy identifies buses and taxis as priority vehicles to target, then HGVs then vans and only then (possibly) cars, so actually in the reverse order of NOx contribution.
It is difficult to escape the conclusion that all the politically difficult decisions have been delegated to local authorities.
The quickest and most cost-effective solution to our air quality epidemic is to put the bus at the centre of the strategy. Progress in clean diesel bus technology has dramatically exceeded diesel car technology. Real world testing of Euro VI diesel buses demonstrates a 95% reduction in NOx emissions compared with Euro V. Currently a journey by a Euro 6 diesel car emits 10 times the per passenger NOx of a comparable journey by a Euro VI diesel bus.
Moreover, putting buses at the centre of air quality strategy would support UK manufacturing. At least 80% of urban buses sold in the UK are built in the UK. And Government financial support for bus retrofitting provides 15 times as much value for money as scrappage allowances for diesel cars.
Government's exclusive focus so far on reducing emissions per vehicle presents a distorted picture. The focus needs to be on reducing emissions per passenger and on moving people not vehicles. Measures to encourage modal switch can be transformative. Bus priority measures can deliver 75% fewer emissions per bus passenger km than for car passengers. A fully loaded double decker bus can take up to 75 cars off the road.
Whilst it may be anticipated that there will be a significant reduction in emissions from the vehicle fleet by 2030, the congestion problem – with all the associated wider social and economic costs and aggravation for road users – is set to get worse. On current trends, the average traffic speeds in our major conurbations are projected to fall from 16.5 mph in 2016 to just 11.9 mph in 2030.
On the twin perils afflicting our towns and cities – congestion and pollution – Government must show leadership. Decisions must be based on evidence, not on political expediency; address head on the issue of diesel cars; and, encourage the switch to more sustainable transport.