File photo: Alexandra Beier / Reuters.

London, England - Exhaust fumes are clogging motorists’ brains and triggering car crashes, researchers say.

An analysis by the London School of Economics found that elevated levels of nitrogen dioxide were linked to an increase in accidents.

It is thought that the brown, foul-smelling gas clouds the mind, blunting attention and slowing reaction times.

Produced by the burning of fossil fuels, most of the nitrogen dioxide in the air comes from road transport, with diesel a particularly rich source of the pollutant.

Air pollution has long been blamed for damaging heart and lung health but with recent studies suggesting it also affects behaviour, researchers at the London School of Economics decided to look for links with motoring performance.

They divided Britain into a grid of 32 areas each covering about 7770 square kilometres and factored in information on pollution levels, weather conditions and accident rates covering the period from 2009 to 2014.

Analysis showed that a rise in concentration of nitrogen dioxide of one microgram per cubic metre was linked to a two percent increase in accidents. To put the figure in context, cutting levels by a third in west London, one of the most polluted parts of Britain, would reduce crashes by five percent.

Some 1730 people were killed on Britain’s roads in 2015 and another 22 100 seriously injured.

Researcher Lutz Sager, an economist at LSE’s Grantham Institute, said: “Although it has already been shown that air pollution adversely affects human health and the ability to carry out mental tasks, this is the first published study that assesses the impact on road safety.

“The analysis identifies a causal effect of air pollution on road crashes, but I can only speculate about the cause of the link. Previous research has shown that breathing in air pollution can affect your ability to concentrate and complete mental tasks.

“That is why I think the most likely explanation is that air pollution affects drivers by reducing their mental alertness or reaction time.”

But Sager said other explanations were possible, such as air pollution causing physical distractions such as an itchy nose or limiting visibility. He explained: “Whatever the exact mechanisms responsible, the robust finding of a significant effect of air quality on road safety is important given the high cost of road traffic accidents through damage to vehicles and deaths and injuries to people every day.

“Although this analysis used data for the UK, I think my findings are relevant to other parts of the world. These additional costs from crashes strengthen the case for reducing air pollution, particularly in congested cities.”

Drivers breathe in pollution through open windows or from air conditioning vents. The study did not investigate whether effects on mental performance could be permanent, or temporary..

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