Curiosities: Which saves more gas: driving with windows closed, and the AC on, or AC off, and windows open?

That depends on conditions. “Today’s cars are designed to be very aerodynamic,” says Glenn Bower, a senior scientist at the Engine Research Center at UW–Madison. “They ‘cut’ through the air at moderate speeds. At lower speed, stopping and starting dominate the vehicle’s energy consumption, while at highway speed (45 to 65 mph) most of the power is lost to the air we drive through.”

Lowering the windows increases drag, but eliminates the gasoline needed to drive the AC, while raising the windows does the opposite. So here’s the expert rule of thumb: “If you are driving about 30 mph or faster, it will be more efficient to put up the windows and drive with the AC on,” Bower says. “On the other hand, if you are stuck in a traffic jam or traveling in downtown Madison between stoplights, it would be more efficient to shut off the AC and drive with the windows down.”