6 Driving Tactics to Save Gas This Summer

Tactic No. 1: Coast to a Stop

Brakes are necessary (duh!), but they're inherently wasteful: They take the kinetic energy of a moving car—energy it took pricey gasoline to generate—and turn it into heat that's lost to the air. Everyone knows that accelerating until the last moment then braking hard to stop is less efficient than slowly coasting to a red light. But PM's test data (illustrated above) prove what a huge difference coasting makes. The lesson: Whenever possible, anticipate that a light will turn red and ease off the gas. Generally, the less you have to brake, the better your fuel economy.

Tactic No. 2: Avoid Slowly Crawling Up to Speed

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Conventional wisdom says that jackrabbit starts consume more fuel. But it turns out that nursing your speed up to the limit too slowly also lowers mpg. How can that be? Cars get poorer fuel economy in lower gears, and accelerating too slowly prevents up-shifting at an efficient rate. The best acceleration rate varies with the vehicle, gear ratios and weight. But in our testing we found that taking 15 seconds to accelerate to 50 mph used less fuel than taking 30 seconds to reach the same speed, because the car entered its top, fuel-​saving gear sooner.

Tactic No. 3: Close Windows and Use A/C at High Speeds

It's a fierce efficiency debate: Open the windows in summer to avoid running your energy-intensive air conditioner, or keep the windows closed and the a/c on to preserve your car's aerodynamic profile. (We'll leave aside the option of sweating it out.) PM's testing settled the issue. Driving at 55 mph with the a/c running, we got 24 mpg; turning it off bumped us up to 28 mpg. Then we opened all four windows, one at a time, and lost 1 mpg per window until we were back at 24 mpg. So at that speed, it's a wash. But aerodynamic drag rises exponentially with speed­—the faster you go, the more the open windows hurt efficiency. The answer? Below 55 mph, open the windows and leave the a/c off. But at 60 mph or higher, keeping them closed and the air conditioning running will burn less fuel.