There's no doubt that car manufacturers have worked incredibly hard over the past few decades to make their cars cleaner than ever.

Modern cars produce a fraction of the pollutants of their predecessors - as little as a tenth of those in 1970 - and they're improving all the time.

We've seen the benefits already in terms of reduced smog levels. However, as well as the respiratory problems car fumes can create, research revealed in the Wall Street Journal (via Treehugger) suggests that car fumes can cause brain damage, too.

Recent public-health studies and laboratory experiments suggest that whatever your age, traffic fumes can have a measurable effect on mental capacity, intelligence and emotional stability.

It's a pretty serious claim but a worrying one all the same. The studies show that breathing street-level fumes for just 30 minutes can result in changes in electrical activity in the brain, akin to those of increased stress. Older men and women exposed to higher levels of traffic-related particles might also be more likely to develop Alzheimer's or Parkinson's diseases.

It also has the potential to harm brain cells and impair learning ability in everyone, regardless of age, shape or size. Even child development can be affected, with the babies of mothers exposed to higher levels of exhaust fumes displaying lower IQ than their peers.

The tests have been repeated all across the globe, by teams in New York, Boston, Beijing and Krakow, Poland.

Some of the results of testing have been rather worrying: Children born to mothers living within 1,000 feet of a major road or freeway in Los Angeles, San Francisco or Sacramento are twice as likely to show signs of autism.

It's certainly an advertisement for improving local air quality in some areas, and there are measurable improvements - traffic rerouting in Times Square has reduced local pollution levels by 63 percent, which has been a breath of fresh air to business people and tourists. A similar system in America's most congested city, Los Angeles, would no doubt be of benefit to tens of thousands of people.

The research is in its early stages and there are plenty of other factors that can cause health problems in people of all ages so it's important not to worry too much just yet.

However, it stands to reason that living near a busy traffic hub might not be that great for your health, and probably won't help your road rage either...

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