Idling at stop lights does affect gas mileage. This is because the engine is still running, but the car is not moving, so the energy from the fuel is not being used to propel the car forward. Instead, it is being used to power the car's accessories, such as the lights, radio, and air conditioning. This can decrease gas mileage by up to 15%.
To help reduce gas mileage, drivers should avoid idling for more than a minute or two. If they know they will be stopped for a long time, they should turn off the engine.
