If drivers of gasoline cars refrained from speeding, they would collectively save an average of 57,000 metric tons of carbon emissions every day in the United States—while spending less than a minute more behind the wheel, a new study reveals.

“We are presenting a somewhat obvious, but impactful, way to reduce energy and emissions that doesn’t require a new vehicle or new technology, just backing off the accelerator pedal,” says study team member William Northrop, professor of mechanical engineering at the University of Minnesota.

The analysis proceeds from a simple and well-known proposition: driving fast is disproportionately energy intensive, as drag force increases exponentially with speed and the engine burns more and more fuel. “That’s physics,” Northrop says.

But no one had ever added up the impact at a national scale before.

In the new study, Northrop and University of Minnesota graduate student Bharat Jayaprakash analyzed a database of more than 120 million actual trips made by light-duty vehicles such as cars, SUVs, and pickup trucks across the United States to gain insight into how often and how fast drivers speed.

They used a computer model to quantify the energy consumption, fuel cost, and carbon emissions from the actual vehicle trips. Then they modeled what would happen if those same trips had all taken place without the drivers ever exceeding posted speed limits.

Driving the speed limit would save an average of 6.7 million gallons of fuel, 57,000 metric tons of carbon emissions, and $22 million in fuel costs daily across the United States, the researchers found.

Why don’t people comply with posted speed limits? Mostly, because they want to save time. But the analysis shows that slowing down would only add about 190 seconds of drive time per 100 miles traveled—which works out to about 54 seconds per day for the average driver.

“The core takeaway is that the individual time savings gained from speeding are statistically negligible, but the collective environmental and economic costs are massive,” Jayaprakash says.

Obeying the speed limit only cuts fuel consumption by about 2.4-3%, depending on the time of year. But across the United States, that all adds up to an annual fuel savings equivalent to taking about 5.5 million passenger cars off the road.

Plus, the savings estimate is likely a conservative one since the researchers only evaluated speeding on roads with posted speed limits of at least 45 miles per hour.

The team also analyzed the effect of speeding on energy use and emissions generated by EVs in California (the only state where there are enough EVs for a statistically significant analysis). This investigation showed that obeying speed limits would yield small but collectively significant savings for EV drivers too: a single day’s savings of 195 megawatt hours of electricity could power 82 EVs for an entire year.

“There is no free lunch here; no matter what vehicle you drive, speeding and aggressive driving cost energy regardless of what energy source powers it,” Northrop says; the stop-speeding strategy remains important even as the vehicle fleet goes electric.

Source: Jayaprakash B. and W. F. Northrop. et al. “Speeding incurs substantial environmental and economic costs nationwide for negligible travel time savings.” Communications Sustainability 2026.

Image: © Anthropocene Magazine.