If your gas mileage doesn’t seem as good as it once was, there might be some very valid reasons — including the fact that you’re driving too aggressively.

A recent experiment conducted by General Motors found that driving a bit more slowly, keeping the correct air pressure in your tires and making sure your trunk isn’t unnecessarily loaded could result in an extra 16 miles per gallon. The annual fuel savings? More than $1,200.

GM says some of the most common things people do that negatively impact fuel economy include accelerating too quickly, idling in drive-through lines, and ignoring routine auto maintenance. For example, tires that are underinflated by as little as 10 pounds can cut your fuel efficiency by more than 3 percent.

“The fuel economy of every vehicle is greatly affected by how you drive, and how you care for your vehicle,” said Roger Clark, manager of the GM Energy Center. “Often, relatively small changes to your driving habits and vehicle maintenance can make the difference between being on the bottom, or the top, of the fuel-economy scale.”

“With a well-maintained car, the best drivers get up to 25 percent more miles per gallon than average,” he added. “When you combine a poorly maintained car with inefficient driving habits, the fuel economy of the worst drivers can be 50 percent below average.”

[Time]