Have a need for speed? Driving above the speed limit costs you

Speeding in your car to work, to pick up your children from school, or to go from one errand to the next not only wastes money in gas and sends harmful emissions into the air, but it also barely saves you time, according to new research.

It is something to think about as gas prices remain elevated throughout the summer months, adding pain to day-to-day driving and seasonal road trips.

Instead, abiding by posted speed limits can save U.S. drivers millions of dollars at the gas pump and eliminate millions of gallons of fuel each day, according to a study published Thursday in the Nature journal Communications Sustainability. That fuel, when burned, emits planet-warming gases into the atmosphere. To top it all off, changing driving habits wouldn’t even add a full minute to a driver’s commute.

University of Minnesota researchers analyzed 120 million vehicle trips across the United States from four Wednesdays in 2021 using driving data on national road networks, speed limits, and U.S. Geological Survey elevation data. The analysis included roads with speed limits of 45 mph and higher.

More than 43% of the studied trips included at least one instance of speeding, and drivers spent nearly 12% of their driving time exceeding the speed limit.

They found that if drivers of light-duty, conventional internal combustion engine vehicles actually drove at posted speed limits, it could save an average of $22 million, based on fuel costs at the time, 6.7 million gallons of fuel, and 57,000 metric tonnes of carbon dioxide every day. The researchers said that it is comparable to taking about 5.5 million passenger vehicles off the road.

And while drivers say that speeding saves them precious time, researchers have found that this is not the case. With an average daily driving distance of 28.6 miles, driving at or below the posted limit amounts to only about 54 seconds longer per day.

“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,” said William Northrop, mechanical engineering professor at the University of Minnesota and study co-author.

The research considered battery-electric vehicle efficiency only in California, given the level of EV adoption in the U.S. at that time. Based on the California modeling, “We find that driving slower is beneficial for EVs as well,” he said.

Interestingly, the study found differences among states. Nevada saw elevated speeding prevalence as well as high speed excess. There was high speeding prevalence in Florida, Georgia, and North Carolina, though those states did not necessarily exhibit high speed excess. Montana, Wyoming, Idaho, and South Dakota showed both low prevalence of speeding and low speed excess.

The cost of faster driving today

Driving faster increases a vehicle’s energy use and engine emissions, and reduces efficiency. Vehicle engines have become increasingly more efficient over the past several decades, even as vehicles have gotten bigger and more powerful. But speed limits have also climbed since the Emergency Highway Energy Conservation Act was implemented, which mandated a 55-mph national speed limit amid the 1970s energy crisis.

Accounting for the average cost of gas today and more vehicle miles traveled, that increases to roughly $26 million and 7.2 million gallons of fuel that Americans collectively could save each day this year just by not putting the pedal to the metal.

One limitation of the research is that slower driving could impact traffic patterns, which could play a role in efficiency.

However, it is especially timely, as U.S. drivers remain price-sensitive amid volatile gas prices, with the war in Iran sending the cost of a gallon of fuel above $4 this year. Experts have said there are several ways to improve one’s gas mileage, including something as simple as slowing down. Less fuel needed to be purchased due to improved efficiency could influence oil market demand, which in turn could impact pricing.

Rob Middleton, associate research scientist of mechanical engineering at the University of Michigan, who was not involved in the research, said the study was well done. But he also noted that the fuel saved by driving more slowly still represents only a fraction of daily gasoline consumption in the U.S., which is about 375 million gallons.

“It’s a big number, but it’s a small fraction,” Middleton said. “This is a ‘freebie’ in that it doesn’t really cost anyone anything to do.”

“The market penetration of selling EVs is still small, so we still need fuel, we still need ICE (internal combustion engine) vehicles, we’re still going to have them for a very long time,” he added. “Things that we can do to either make the new ones better or to improve our fuel supply, we need to do.”

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