Pollution that gathers inside cars in traffic jams and at red traffic lights is far higher than that found in cars that are moving. Now, research published in the journal Environmental Science: Processes and Impacts offers a solution: keep the windows closed.

Research led by Dr. Prashant Kumar, from the University of Surrey, UK, has shown that 25% of exposure to harmful particles when driving occurs in the 2% of the journey time that drivers spend passing through intersections with traffic lights.

Pollution at intersections is 29 times higher than on the open road. At intersections, vehicles slow down, stop, rev up to move when lights turn green, and they are closer together.

These locations scored between 101-150 on the index, considered “unhealthy for sensitive groups””Good” scores are from 0-51, and 151 or over is “unhealthy.”