Commuters across the U.S. are feeling the crunch at the gas pump as the war in Iran drives up prices. If only there were a simple way for drivers of gas-powered cars to cut down their fuel costs while also reducing planet-warming carbon emissions.
A new study says there is. The findings, published Thursday in the journal Communications Sustainability, show that if U.S. drivers of gas-powered passenger vehicles actually drove the speed limit, it could save an average of 6.7 million gallons of gas, 57,000 tons of carbon dioxide (CO2) emissions, and $22 million per day, based on fuel costs during the study period. That’s equivalent to taking about 5.5 million cars off the road, according to the researchers.
While it may feel like speeding shaves a significant amount of time off your commute, the study suggests that driving at or below the speed limit lengthens commute times by just 54 seconds per day, or 6.3 minutes per week, based on the average daily driving distance of 28.6 miles (46.03 kilometers).
“If your goal is to shave one minute off your time, then you’ve got to drive fast. If your objective is to get to your destination safely and to save fuel, then you might drive slower than the speed limit,” co-author William Northrop, a professor of mechanical engineering at the University of Minnesota, told the Associated Press.
The U.S. has a speeding problem
Speeding is highly prevalent in the United States. Research by the personal injury law firm H&P Law showed that nearly half of American drivers admitted to driving 15 miles per hour (24 kilometers per hour) above the speed limit within the past month in 2023.
Speeding increases fuel consumption due to atmospheric drag, making high-speed driving more energy intensive. A 2021 analysis showed that aggressive driving behavior—speeding and rapid acceleration and braking—can lower fuel economy by 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic.
“We already understand the physics of how speed affects fuel consumption, but quantifying the exact magnitude of those savings at a national scale gives us a clearer picture of the actual impact,” Bharat Jayaprakash, a PhD student in the Department of Mechanical Engineering at the University of Minnesota and lead author of the new study, said in a press release.
To that end, Jayaprakash and Northrop analyzed over 120 million real-world vehicle trips that occurred during a four-day period in 2021. The study included gas-powered passenger vehicles across the continental U.S. and Hawaii—which account for 14.6% of total national energy consumption—and electric vehicles in California.
Among the gas-powered vehicles studied, 43.2% of trips had at least one speeding event, averaging a maximum speed excess of 11.2 mph (18.02 kph). Interestingly, the researchers found that the prevalence of speeding differed by state, with speeding noticeably higher in Florida, Georgia, North Carolina, and parts of Alabama and Virginia.
Slow down and save
Now that they had a clearer picture of speeding across the U.S., the researchers evaluated two speed limit interventions designed to reduce fuel consumption and CO2 emissions. The first is simple: drive at or below the speed limit. According to the study, this alone could yield average nationwide savings of 6.7 million gallons of gas, $22 million, and 57,000 tons of CO2 emissions per day.
The second intervention adds to the first by having drivers ease off the accelerator earlier and coast to slow down, as opposed to driving at high speed until the last moment and braking hard. According to the analysis, this smoother driving style could increase average nationwide savings to 8.2 million gallons, $27 million, and 69,000 tons of CO2 per day.
The researchers found that driving slower could be beneficial for electric vehicles as well. Their analysis of California’s EV fleet revealed that adhering to posted speed limits could save 160 to 200 megawatt hours of electricity and 50 to 90 tons of CO2 emissions per day, rising to 190 to 230 MWh and 60 to 100 tons of CO2 per day when drivers implement a smoother driving style.
Jayaprakash and Northrop note that their study does not account for how slower driving could impact traffic patterns, which may have unintended consequences for vehicle efficiency. Still, the findings illustrate that speeding contributes significantly to fuel consumption, costs, and CO2 emissions in the United States while shaving mere minutes off commutes. Next time you’re worried about filling up your tank, consider slowing down.
English (US) ·