TORONTO -- Traffic-related air pollution poses major health risks for the one-third of Canadians who live or work close to high-traffic roads or highways, say researchers, suggesting there are steps that can be taken to mitigate the danger.

Pollutants from vehicles' tailpipes have been linked to the development of asthma in children and adults, says a commentary in Monday's issue of the Canadian Medical Association Journal.

Exhaust is also known to increase the risk of heart disease and lead to hospitalizations for pneumonia in the elderly, as well as being linked to premature birth and low-birth weight infants.

"Those are all pretty big deals, so things like lung cancer and heart disease are important killers in Canada," said lead author Michael Brauer, an environmental health specialist at the University of British Columbia.

"And we know that if children are born prematurely or at low birth weight, that could have implications throughout their lives, so it puts them at risk for a lot of other potential health outcomes," he said from Vancouver. "And asthma is for children, especially, a very important chronic disease."

About 10 million Canadians -- or 32 per cent of the population -- live within 500 metres of highways or 100 metres from major urban roads, exposing them to elevated levels of traffic-related air pollution, Brauer said. Air pollution is blamed for about 21,000 premature deaths in Canada each year.

Although pollution from exhaust is not the prime risk for such diseases -- smoking plays a much greater role in the development of lung cancer, for instance -- "if you add up the fact that a third of the population is exposed, then on a population basis it becomes very important," he said.

"It's much more effective to remove this risk than it is to treat 10 million people."

Michael Jerrett, head of environmental health sciences at the University of California, Berkeley, said several studies have linked ongoing exposure to traffic pollution to an increased risk of cardiovascular disease, high blood pressure and diabetes.

"So I think the evidence is rapidly accumulating that traffic pollution in particular is bad for a wide variety of health outcomes that range from low-term birth weights all the way to premature mortality when we're elderly, and then cancer and heart disease and lung disease in between," he said Monday from San Francisco.

Brauer and his co-authors highlight four strategies with short- and long-term options to help reduce the effects of traffic-related air pollution:

  • Reducing vehicle emissions: introducing programs to remove or retrofit high-emission vehicles; reducing traffic congestion; expanding infrastructure for electric cars.
  • Modifying current infrastructure: limiting heavy truck traffic to specific routes; separating active commuting zones -- for instance walking and cycling routes -- from busy roads.
  • Better land-use planning and traffic management: locating buildings such as schools, daycares and retirement homes at least 150 metres from busy streets.
  • Encouraging behavioural change: creating policies to reduce traffic congestion in specific areas and encouraging alternative commuting behaviours.

Brauer said about 200 cities in Europe have implemented fees for drivers who enter a "congestion-charge zone" in busy inner-city cores. The best known of these may be London, which has reduced traffic volume and congestion that resulted in "an estimated gain of 183 years of life per 100,000 residents within the zone over a 10-year period."

Other urban centres have designated zones that allow only low-emission vehicles, among them gas-electric hybrids.

"Ultimately, I think it's something that should be thought of when we're (urban) planning," said Brauer.

For instance, new residential developments should be set back from high-traffic roads, he said, noting that exhaust expelled from vehicles is diluted in the air after it reaches a certain distance.

Building urban neighbourhoods that encourage walking, cycling and public transit instead of cars could also lead to lower air pollution levels, he said.

"It's really a matter of changing our mindset," said Brauer. "We're very focused still on designing transportation all around cars and we probably should be designing transportation around people."

But Jerrett said health hazards in exhaust fumes aren't confined only to those living close to busy roads and highways.

"The other thing to consider about traffic pollution is it's not just where you live ... it's also all the pollution you're exposed to during the commute," said the Canadian-born researcher, pointing out that on major highways like the 401, especially where it runs through Toronto, "levels in the middle of the roadway will be 100 times higher than background sites."

Unless a vehicle has hepa-filtered ventilation, people will get some of the highest doses of pollution they are exposed to all day during their daily commute, he said.

And while there's no denying the health benefits of exercise such as cycling, those who regularly bike on busy roads also get higher exposure, he said. "So you're not just getting the elevated pollution from being (on the) ... road, but you're also going to be taking in more of that pollution. So your actual inhaled dose can go up.

"It's a good idea to encourage walking and biking, but it has to be done carefully because ... we don't want to get people in harm's way ... and put them out on busy streets where there's a lot of pollution."