The Rule of Thumb That Can Save You Money on Gas

The key to coping with high gas prices is better driving habits.

A turtle shell acts as the body of a car
Adam Maida / The Atlantic; Getty

Halfway from Los Angeles to Las Vegas, I was running out of gas. A couple of hours before, when I’d left home in my Ford Escape plug-in hybrid, the range predictor told me I had miles to spare in the tank. But, late for an appointment, I’d been driving fast in Interstate 15’s far-left lane, where the prevailing culture dictates that the 70-mph speed limit is merely a suggestion. As a consequence, I had less than 100 miles of fuel left and 130 miles to go.

I considered stopping to fill up. But every gas station Google Maps found on my route through the sparsely populated Mojave Desert required a 10-to-15-minute detour, which would put me even further behind time. Doing a quick calculation as the collective pace of the fast lane neared 90, I realized that the best chance I had of making my appointment was to move to the right and tuck in with the trucks. So I did what on a California freeway these days qualifies as radical, aggravating, and to some drivers, even dangerous: I slowed down.

Fast speeds use more energy to cover the same distance than reasonable speeds do. Most of us learned this simple fact as student drivers, but somehow over the years, we’ve come to regard aggressive driving as the nobler of sports. Never mind that it kills people—more than a quarter of traffic fatalities in 2020 were related to speeding, according to the National Highway Traffic Safety Administration. Or that it wrecks the climate—data from the German Environment Agency show that lowering the national speed limit to 100 kilometers per hour (roughly 60 mph) would reduce the country’s carbon emissions more than taking 1 million cars off the road. We love speed.

But as the geopolitical situation deteriorates in Eastern Europe, perhaps we might consider again the righteousness of driving at more reasonable speeds—if only to weather the “Putin price hike,” as the Biden administration has branded the inevitable spiking of gas prices already in progress, and support our national resolve to ban oil and gas imports from Russia. Because in the coming months and maybe even years, slowing down will save you money—potentially, depending on the car you drive and how much you drive it, lots and lots of money.

According to a 2013 study by Oak Ridge National Laboratory, which evaluated for speed and efficiency 74 vehicles as disparate as diesel Volkswagens, hybrid Ford Fusions, and the gas-powered Mercury Grand Marquis, a typical U.S.-made car achieves maximum fuel efficiency at a steady speed of 40 to 50 mph. After that, explains John Thomas, the now-retired lead investigator on the study, “the rule of thumb is that you lose about 15 percent gas mileage for every 10 miles per hour you accelerate.” On the open road, where drivers maintain steady speeds of 50 to 80 mph, reducing speed by 10 mph can save 75 cents a gallon on a five-dollar gallon of gas—or 90 cents a gallon on a six-dollar gallon of gas, already the price where I live, in the San Fernando Valley area of Los Angeles.

This varies a lot by the make and model of your car, whether you have a headwind or a tailwind or crosswinds, and countless other variables. But basically, Thomas says, “peak fuel economy is the lowest speed you can go in the highest gear.” It’s where your revolutions-per-minute dial hovers in the lower third, where you can hear your engine purring, but never hear it rev. “It’s actually a little bit nonlinear,” Thomas says. “Efficiency gets worse as you keep going faster.”

On urban roadways, where driving speeds are controlled by semaphores and stop signs, practitioners of “hypermiling” brag that, under optimal conditions with a hybrid electric-gas engine, they can reduce fuel consumption by as much as 60 percent. Wayne Gerdes, the progenitor of hypermiling (he coined the term in 2004), has endorsed driving as though there’s an egg under your accelerator that you don’t want to break. And when you see a red light, lift your toes and coast to a stop. Even in a hybrid with regenerative braking, stopping can never return 100 percent of the energy to the battery, even if your vehicle tells you it did. The brake is there only for emergencies.

When you get good at this skill, as I have, you’ll find yourself smugly coasting past the aggro drivers who passed you as they raced to the red light. “If you dial back the aggression in your driving, you don’t really lose time,” says Michael Manville, an urban-planning professor at UCLA. “But you do save a bunch of money.”

None of this is news, really. In 1974, after Saudi Arabia and other Arab nations blocked oil sales to countries that backed Israel in the Yom Kippur War, then-President Richard Nixon signed the Emergency Highway Energy Conservation Act, one provision of which lowered the national speed limit to 55 mph to mitigate the problem of long lines at the gas pumps.

But we’ve been reluctant to keep it there. Nowadays, the social pressure to speed in the fast lane has become a sort of moral imperative; even driving the speed limit in some places is considered a traffic hazard. Manville thinks the first step to altering that culture is simply to enforce existing limits more consistently. Transportation Secretary Pete Buttigieg has proposed giving money to states to install speed cameras; Manville is all for it. “As long as you don’t fiddle with the camera,” he says, “you remove fears of discriminatory enforcement.” You eliminate the possibility that something can “go tragically wrong” during a simple traffic stop. “And if a camera catches everyone who speeds on a road segment, every time they speed, then you can actually get meaningful deterrence,” Manville says.

Which means you don’t have to pay $250 for every enforcement. “The logic behind the high fines for speeding right now is that you don’t catch most people who speed,” Manville says. If drivers knew that there was a 99 percent chance they’d get nailed for excessive speed, the ticket could be just $25. You might risk it once, or even twice, if your wife was in labor, say, or your neighbor cut his hand on the immersion blender and needed to get to the ER. But after a few violations, it would start to get expensive.

All the pokey driving in the world, of course, can’t compensate for more concrete influences on fuel efficiency—the vehicle’s aerodynamics, the size of its hybrid battery, the cargo box on your roof where you keep your mobile tool shed. “What really matters in terms of burning up fuel are decisions that are kind of hard to undo on short notice,” Manville says. Eight of the top 10 best-selling cars in the U.S. are petroleum-burning trucks or SUVs, and most people who still drive 20-year-old beaters can’t afford to trade them in for electric vehicles. Even if they could, EV-charging infrastructure is still intermittent and flaky. Nothing induces range anxiety like exiting the freeway to the promise of a fast charger, only to find the charger broken, occupied, or outfitted with a connector that doesn’t fit your vehicle.

Nor can we suddenly redesign cities to encourage nonmotorized transportation. I bike as much as I can in Los Angeles, where road racing is common and protected bike lanes are few. But it feels a little like cliff diving—fun, and good exercise, but with uncertain survival outcomes.

We talk a lot about the future of cities, but for many people, the future is now, and it’s about to get a lot more expensive.

As for my trip to Vegas, at a steady 62 mph from the state border on, maximizing coasting and crawling up hills in the truck lane, the range estimate on my fuel gauge ticked up all the way to my destination. I arrived on time and with gas to spare, room on my credit card, and a resolve never to speed again.