Now we know what's really coming out of some car exhaust pipes. It's clear we can't afford to spend billions building new roads for ever more cars if we want clean air and a stable climate.
The scandal at VW has thrust air quality into the headlines. The company decided it was better to cheat emissions tests than comply with laws protecting people's health. In so doing, they judged that their profits were more important than human lives.
Recent exposés aren't limited to dirty diesels. New research by Transport and Environment shows the official tests on fuel efficiency appear just as wonky, over-estimating real world mileage - and with it carbon dioxide emissions - by a massive 50 per cent.
But the real story should not be shock that car manufacturers have been lying to us - it's the realisation of what our reliance on cars is doing to our air and our climate. Earlier this month, DEFRA confirmed 29,000 people die prematurely from particulate matter pollution, and 23,500 from nitrogen dioxide every year because they routinely breathe dirty air from road traffic. Our carbon reduction targets require us to reduce emissions from road transport to virtually nothing by 2050. But as the Committee on Climate Change reported on 15 September, increases in miles driven mean emissions from transport are actually rising.
In this context, the Government's policies look not just weak, but counterproductive.
DEFRA's draft Air Quality Plan - intended to get levels of nitrous oxide down to legal levls by 2020 - has no new powers or funds to improve air quality, and gives financially hamstrung local authorities the lead responsibility for tackling a national air pollution problem. Second, through the Road Investment Strategy, the Government is planning a major programme of road building to increase the number of cars - including in areas already identified as having dangerously dirty air, for example the A14, A27 and a number of Smart Motorway schemes such as the M4.
In short, the Government is planning more roads and more cars in areas where public health is already at risk and when road transport is flashing red against the UK's climate change targets.
A Government response limited to a few local plans and tighter vehicle testing clearly does not go far enough. Draft Air Quality Plans need to be beefed up to include proper funding for a national network of clean air zones. There is a strong case for cross-departmental action looking at areas like future fuel taxation, funding for sustainable transport, the impact of major road building plans, whether modelling and monitoring are up to the job, and if land-use planning guidance does enough to encourage development based around public transport, walking and cycling. Hopefully, a new Transport Select Committee inquiry into transport emissions might pose some of these questions, but we should all be asking if new roads and more cars are compatible with healthy air and a stable climate.