London: Apart from wasting your time, long traffic jams may cause exposure to toxic fumes, and potentially increase various health risks, including cancer, say researchers, one of them of Indian origin.

Exposure to outdoor air pollution is among the top ten health risks faced by humans and is especially pronounced in urban concentrations, according to the World Health Organization (WHO). In October 2013, WHO classified outdoor air pollution as being carcinogenic to humans. 

The findings showed that when vehicles stop at red lights, they go through different driving cycles such as idling, acceleration and deceleration and emission of toxic fumes. 

These emissions take more time to disperse, especially in built-up areas and end up accumulating in the air at traffic signals.

Thus, the people sitting inside cars, with closed windows but with fans switched on, can be at an increased risk of exposure to the outdoor pollutants, the researchers said.

Switching on the fan sucks the dirty air from outside to inside the vehicle, resulting in an accumulation of pollutants in the car.

However, it may be relatively safe to put fans onto the setting where they re-circulate air within the car without drawing polluted air in from outside, the study stated.

"Where possible and with weather conditions allowing, it is one of the best ways to limit your exposure by keeping windows shut, fans turned off and to try and increase the distance between you and the car in front while in traffic jams or stationary at traffic lights," said Prashant Kumar from the University of Surrey. 

"If the fan or heater needs to be on, the best setting would be to have the air re-circulating within the car without drawing in air from outdoors," Kumar added.

Previous studies have shown that drivers stuck at traffic lights were exposed up to 29 times more harmful pollution particles than those driving in free flowing traffic. 

The new research, published in the journal Environmental Science: Processes and Impacts, has found that pedestrians are also exposed to increased air pollution around traffic signals.