How did Volkswagen fake its emissions data?

The car manufacturer's CEO has stepped down following revelations that the company had concealed the true emissions of 11 million of its vehicles. 

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German car manufacturer Volkswagen (VW) is in the midst of perhaps its biggest scandal ever. US regulators have found that some VW diesel vehicles were programmed to restrict emissions only when the vehicles were under testing conditions, and VW admitted that this was the case – and that up to 11 million vehicles could be affected. Yesterday, CEO Martin Winterkorn stepped down. Germany's stock market has hit its lowest ebb since late August. 

So how did they get found out?

The Council on Clean Transport, the US-based NGO which uncovered the scandal, actually set out to establish that modern diesels were relatively clean, and had low enough emissions that they could be considered a positive choice for pollutant reduction. 

Instead, they found that the VW models they tested gave very different emissions readings when they drove them between San Diego and Seattle, and in an official testing laboratory. Awkward.

Following the revelations, Volkswagen admitted to systematically cheating the US air pollution tests. Apparently, the affected models include the Beetle, Jetta, Golf and Passat. VW has said that 11 million of the affected models were sold worldwide, and 480,000 have so far been recalled in America. 

How did they do it? 

Turns out that the vehicles were fitted with software which turns on pollution controls only when the car is being officially tested for emissions. This doesn't actually contravene the letter of the regulations, which states that cars may not exceed certain emissions levels under test conditions – but I think we can all agree it goes against the spirit, breaking other laws along the way. 

The Environmental Protection Agency (EPA)has said that in fact, during normal driving, Volkswagen diesel models pollute between 10 and 40 times the legal limits. 

What does that mean for the environment?

Nothing good. Analysis from the Guardian suggests that the cars could be responsible for nearly a million tonnes of pollution per year. This is apparently equivalent to the emissions of every UK power station put together. 

This also offers a disturbing insight into an industry that needs to change its tune if we're to combat climate change. If hidden emissions are a wider problem across the car industry, we could be looking at an environmental disaster of cataclysmic proportions. It would mean the cars on our roads are both emitting far more pollution than we realised, but also that we may need to replace a huge number of them moving forward, which could be equally as damaging. 

What happens next? 

The scandal has set off bombs across the industry. Allegations are flying about which other car manufacturers may have used similar methods to game their emissions results, including accusations against BMW. The company has denied rigging their emissions results. 

VW, meanwhile, is in dire straits. The company has set aside £6.5bn to deal with the fallout, though it's impossible to project how much this will cost the company in the long term: they could be sued by every owner of the affected models, and it's possibly that the company could face criminal prosecution. 

More questions will presumably be raised about the emissions tests themselves. The EPA said last year that it would overhaul the tests. European leaders have demanded an EU inquiry into the rigged air pollution tests, yet today, the Guardian revealed that the UK, France and Germany all lobbied in the past to keep loopholes in equivalent car emissions tests in their own countries. 

Barbara Speed is comment editor at the i, and was technology and digital culture writer at the New Statesman, and a staff writer at CityMetric.