It's a common misconception that using cruise control on the highway is more gas efficient. In fact, according to fuel economy testing by the U.S. Department of Energy, drivers can actually save fuel by not using cruise control. The main reason for this is that most people drive with a light foot when they're using cruise control, which means they're not getting the most efficient use of their car's engine. When you're not using cruise control, you can vary your speed slightly without affecting your overall travel time, and this can help you save gasoline.