It’s official‚ cough. Sitting in traffic jams is bad for your health.

Research from the University of Surrey in the UK has revealed that levels of pollution inside cars that are stuck in traffic jams or parked at red traffic lights are up to 40% higher than in free flowing traffic conditions.

That’s enough to make any motorist think twice about hyperventilating while trapped in gridlock in Cape Town. Cape Town has just been ranked as the most congested city in South Africa – and the 47th worst in the world – in the annual traffic index from Dutch navigation equipment maker TomTom.

Johannesburg was ranked 77th out of 174 cities listed.

But it’s not all bad news.

According to the UK study‚ led by senior author Dr Prashant Kumar‚ a simple adjustment to your car’s ventilation system can reduce your exposure to toxic fumes by up to 76%.

“In traffic jams‚ or at red traffic lights with other vehicles stationary in front‚ research has shown that if we close the car windows and switch off the fan‚ this gave us the lowest exposure to pollutants‚” said a statement by the University of Surrey on Thursday. “It is also safe to put fans onto the setting where they re-circulate air within the car without drawing polluted air in from outside.”

Dr Kumar said: “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.

“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‚” he added.

TMG Digital reported last week that Cape Town residents spent an extra 40 minutes in traffic every day than the worldwide average‚ and Johannesburg motorists lost 35 minutes to congestion – the equivalent of six days a year.

“In London‚ it has been reported by the World Health Organisation that air pollution kills more than 10 times the number of people dying from road traffic accidents‚ with an estimated 3.7 million premature deaths in 2012. The problem of air pollution is also prevalent across Europe where over 400 000 premature deaths were attributed to fine particulate matter alone in 2012 and the situation is not very different in other parts of the world‚” said the university.