A Must Read: Car Windows Down vs. A/C On

Increasing a car's fuel efficiency is a top priority as gas prices continue to break records. While sitting in traffic, listening to your car's A/C hum away, you've probably asked yourself whether it is more fuel efficient to roll the windows down or leave the A/C on. Rolling down the windows will increase drag on the car, but leaving the A/C on will drain power.

Slate's Green Lantern answers this question in a great post HERE.