Hanover, Germany  - People suffering from a chronic respiratory ailment should turn on their car's ventilation fan and close the windows before passing through a road tunnel, the German Lung Foundation (DLS) said.

The reason for the precaution is the especially high levels of harmful pollutants in tunnels, the DLS pointed out. It advised motorcyclists to avoid entering tunnels altogether when traffic is congested.

A recent Australian study cited by DLS Chairman Harald Morr showed how high levels can be. "The study measured the level of pollution in a Sydney road tunnel four kilometres long," he said. "When traffic was heavy, levels were a thousand times higher than in downtown Sydney," a city with a population of nearly four million.

Traffic jams increase the amount of pollutants in the air considerably, Morr noted. Particularly harmful is the fine particulate matter emitted by motor vehicles' combustion engines, which can cause breathing difficulties in people with chronic respiratory ailments or heart disease. Inhaling the emissions can also raise the risk of a heart attack or stroke, Morr said. (dpa)