Anybody else tired of talking about gasoline? The price is up; the price is down—but it might go up again, look out! There’s nothing anyone can do about how much it costs because the market is a wild animal with mathematics for teeth. Blah blah blah.
Last year it seemed like we were cruising away from petroleum: The administration was making the right noises, we saw incredible growth in the renewable energy sector, and tons of EVs were rolling towards the market. Then Putin invaded Ukraine. In addition to the brutal toll this unnecessary conflict is taking on the Ukrainian people, the ensuing geopolitical bullshittery has thrown a hammerlock on the global oil supply and “forced” the U.S. government to boost fossil fuel expansion. The political power of $5 gas is one of the most frustrating facts of life for anyone concerned about the environment. Or maybe it’s not.
As this all started cascading, I thought of the 1973 Oil Crisis. For those of you who, like me, were not alive back then (or were very little or are maybe foggy on the details), that’s when OAPEC dropped a petroleum embargo on countries that supported Israel during the Yom Kippur War. The U.S. was on the list, and stateside gas prices climbed from an average of $0.38 per gallon to $0.55 in the space of a year. Those cash registers rang cheap by today’s standards, but it was still a 40-plus-percent increase.
The math on driving slower on the highway is clear: It lowers your fuel consumption—full stop. (Snort. Sorry. -ish.) The wizardry of modern vehicle engineering means this isn’t a simple high school physics equation, but it is broadly accurate that you need more energy to go faster at highway speeds. This was true in the 1970s, when American cars paid more attention to being awesome than being efficient, and it’s true now, when most cars can at least cosplay at gas-sipping.
Scientists at Oak Ridge National Laboratory recently published a paper in which they measured the fuel economy of 74 modern gasoline-powered passenger vehicles across a range of speeds. They confirmed that slowing down works. Assuming you don’t want to wade into 17 pages of technical writing, here are the highlights:
Between 50 and 60 mph, fuel economy drops by an average 12.4 percent
Between 60 and 70 mph, it goes down by an average of 14 percent
Between 70 and 80 mph: down an average of 15.4 percent
Every car is different, so it’s tough to make a blanket statement about how much your personal mileage will change, but the Oak Ridge Gang obliged with a serviceable rule of thumb: “Most vehicles will lose 12-16% (14% ± 2%) in fuel economy for a 10 mph increase within the speed range of 50-80 mph.” So if you’re hitting the pathetic national average 25.7 miles per gallon at 50 miles per hour, you can expect to get roughly 22.5 mph at 60, 19.4 at 70, and 16.4 at 80.
This paper did not consider hybrids or EVs, but those cars can save energy too (also likely petroleum, depending on how and where they charge). Some mileage-tanking factors remain true no matter what you’re driving: Tires deform at speed, putting up more of a fight against rotation; and though our modern rides cut super slick profiles, any vehicle will experience more air resistance—or drag—as its velocity increases.
You can feel this yourself: Stick your hand out the window, palm perpendicular to the road, at 50 miles per hour. Feel the air pressing against it? Now rotate your paw so your palm is parallel to the pavement. You’ll definitely feel less force in the second position, but not zero. By pivoting your hand, you are lowering its coefficient of drag, easing its path through the air. Now repeat the experiment at 80. You’ll feel more resistance both ways. (Look out for bugs—they are like little chitinous missiles.)
So, this is totally happening, right? We’re all going to be puttering along, humming Sammy Hagar by summer’s end, yah?
Probably not. The call on lowering the national speed limit is that it didn’t actually work.
“I suspect that if someone were looking into a new speed limit policy, they’d find this paper pretty quick,” says Jason Shogren, professor of economics at the University of Wyoming. He was also Senior Economist for Environmental Affairs in the Clinton White House, and he’s referring to an influential 1984 study by University of Kentucky economist Glenn Blomquist entitled “The 55 mph Speed Limit and Gasoline Consumption.”
The paper made use of national highway data plus actual consumption numbers from gas stations during the peak oil crisis years of 1973, 1974, and 1975. Here’s your executive summary: “The effect on gasoline consumption [was] found to be surprisingly small.”
The federal government had estimated that dropping the speed limit would reduce gas consumption by 1 to 3 percent. That may seem like nothing, but in 1973, Americans were burning 3.2 billion barrels of oil per year on transportation, or 60.8 billion gallons. A 3-percent reduction would have saved 1.8 billion gallons of gas per year. (By that math, we’d be looking at saving 2.9 billion gallons in 2022.)
Consumption did go down, by 3.3 percent in 1974. But the impact of the speed limit on this reduction was much less significant, according to Blomquist: an average of 0.04 percent from 1973 to 1975. That’s like 23 million gallons of gas per year. In absolute terms that’s significant, but it’s hardly a political win.
This doesn’t mean that driving slower doesn’t work. Again, sparing you 19 pages of equations, Blomquist concluded that other factors, mainly the price of fuel, did more to slow people down and save fuel than the new signs along the side of the highway did.
So in that sense, a ruthless environmentalist like me could view today’s high gas prices with a bit of a grin: They will likely do more to curb fuel consumption than any policy would. Which is good when your government isn’t super into enacting policies.
Shogren agrees. “If your goal is to save the planet, you should be happy that gas prices are high. This is exactly what a carbon tax would do.”
I’m not expecting a national speed limit drop anytime soon. But I’ll be slowing down. In fact, on a recent family road trip through New England, I tortured my wife and daughter by comparing our fuel economy at 55 versus 65. This was an incredibly un-scientific experiment, but, over the course of 100 miles of highway driving, I got, on average, 16.8% better mileage at 55 than 65. Our family whip is not the most efficient on the road, but for some stretches of slower driving, I was seeing 40-plus miles per gallon for the first time ever.
I was also seeing my share of sour looks and hand-mounted bird effigies. Driving 55 sucks, even on roads where it’s the actual speed limit. If you’re on a rural two-laner, some motorists feel like it’s OK to get right up on your bumper and try to pressure you to go faster. If you’re on a major artery (I tried this experiment on I-95 😬), you might consider putting your hazards on if you don’t want to wear a tractor trailer as a tutu.
Shogren has another idea. “Maybe put a sign in your window: I’m driving 55 to save the planet.” It’s not a bad idea. I would make bumper stickers with something like that written on them, but who wants to add more plastic to the world. (Check out one5c’s free, sustainable bumper sticker, though…) I do, however, plan to spend more miles driving slower, because the math on this is pretty compelling:
Per the Federal Highway Administration, more than 70 percent of U.S. driving happens on interstates and major arterials; for an average American, that’s around 10,000 miles. If we use the EPA’s 25.7 mpg average and a conservative savings of 12%, we could all save 47 gallons of gas per year by slowing down on the highway. At today’s national average gas price, that’s around $215 per year. Here’s a better figure: you’ll keep nearly a half a metric ton of CO2 out of the air. If a million of us can save 47 gallons of gas a year, that 417,689 metric tons.
I’m not going to do all of my highway driving at 55. Sometimes I’m in a hurry. Sometimes it’s dangerous. Sometimes I’ve had too much coffee or my kid is yelling about her imaginary giraffe friend and I have got to be the fastest person on the road. But I’m going to take it slow as much as I can—and I’ll be stoked if I can save a couple dozen gallons of gas each year.
Imagine if others took a similar approach. There are 284 million vehicles driving around our country, which means the opportunity to avoid emitting millions of tons of greenhouse gasses is literally (wait for it) stratospheric (sorry). So yeah, maybe I’ll go make that sign now.
Take care of yourselves, and the rest of us too