Sitting in traffic is bad for more than just your arrival time. Long commutes have been linked to lower happiness and higher risk of heart attack. And, according to new research from the University of Surrey in the UK, the air pollution from heavy traffic isn’t just outside your car. Sitting in traffic can up your exposure to polluted air by 40 percent compared to when the roads are clear, according to a study published in the journal Environmental Science: Processes and Impacts.

Closed windows don’t entirely keep out air pollution, the study’s authors found, as the fan still sucks in dirty air and circulates it around the car. When cars are idling, accelerating, and decelerating in the same area, including in traffic and at red lights, all those extra emissions accumulate and are slower to disperse than when traffic is light. This study builds on previous research by the same group showing that crowded traffic signals expose people to 29 times more harmful particles than when cars were moving freely.

Unfortunately, the study's authors don't yet have all the answers on how to solve the problem. Their current recommendations, made in a press release, aren't realistic for those traveling when it’s cold or hot or stuffy: "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," senior author Preshant Kumar explains. "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.”

When car windows were closed and the fan shut off, there was a 76 percent reduction in the number of pollutants in the air inside.

Know of something you think we should cover? Email us at tips@mentalfloss.com.