According to Consumerist, there are lots of ways to wate gas, including keeping your trunk full and idling excessively. But, the number one waste of gas is the classic one a lot of us tend to ignore:

The U.S. Department of Energy reports that the average driver can improve mileage by 3.3 percent simply by inflating their vehicle’s tires regularly. In fact, according to the AAA, under-inflated tires are the No. 1 way we waste gas. One out of every four cars and one out of every three pickups, vans, and SUVs have at least one extremely low tire.