The Big Lie About Your Car’s MPG

Those gas mileage stickers on the windows of new cars, and the MPG info you see in commercials, well here’s how our government certifies those numbers.

For city MPG they run a test that’s not too bad: the car starts with a cold engine, then gets driven for 31 minutes. They make 23 stops, spend 18% of the time idling to simulate being stopped in traffic (probably lower than reality), overall they average 20 mph (a bit slow, considering city speed limits are usually 35 mph), and simulate a short trip on a highway (which helps cheat up the car’s overall mileage). So the city test isn’t perfect, but it’s the lesser of two evils.

The highway MPG test’s another story. They test a car whose engine has already been warmed up, and drive it 10 miles at an average speed of 48 mph. That’s right, 48 mph. Talk about a free pass to the auto industry. If the speed limit on most highways is 65 mph, why in the world would you test at an average speed of 48 mph? Because the faster you drive, the worse your gas mileage becomes due to wind resistance. In essence, the EPA, and whoever makes your car, lie when they tell you what kind of gas mileage to expect. When you hear about a car’s highway gas mileage, most people assume it’s based on driving the speed limit. It’s deceptive, and worst of all, purposefully deceptive to help automakers meet federal CAFE standards.

Here’s a link to the EPA’s explanation of their testing methods.