WASHINGTON — As if drivers needed another reason to hate being stuck in traffic.

A new study finds pollution levels inside cars at red lights or in traffic jams are up to 40 percent higher than when traffic is moving, The New York Times reports.

The study in the journal Environmental Science: Processes & Impacts determined the increased harm caused by sitting in traffic that is standing still.

British researchers looked at the effects of traffic on concentrations of polluting particles, and analyzed how car ventilation settings affected those concentrations.

In the study, drivers were only at intersections 7 percent of total commuting time, but that time accounted for up to 10 percent of their exposure to the dangerous pollution.

For a car stuck in traffic, shutting the windows and turning off ventilation fans reduced the concentration of the smallest, most harmful particles by up to 76 percent.

Leaving the ventilation system running while drawing in air from the outside was not as effective as making the passenger cabin airtight, the study found.

Exposure to harmful particles was six times greater in cars with open windows than for passengers walking through the same three- or four-way intersection.

The average driver in the Washington area spends 75 hours a year stuck in traffic, far above the national average of 50, according to the traffic analytics company INRIX.