Speeding on American roads is not only costing drivers millions at the pump and exacerbating climate change, but it also barely shaves any time off daily commutes, according to new research. This finding is particularly pertinent as gas prices remain elevated throughout the summer months, adding financial strain to everyday driving and seasonal road trips.
A study published in the Nature journal Communications Sustainability reveals that adhering to posted speed limits could save U.S. drivers millions of dollars in fuel costs and eliminate millions of gallons of fuel daily. This reduction would also prevent the release of tens of thousands of metric tonnes of planet-warming gases into the atmosphere. Crucially, changing these driving habits would add less than a minute to a driver’s daily journey.
Researchers from the University of Minnesota analyzed 120 million vehicle trips across the United States from four Wednesdays in 2021. Utilizing driving data on national road networks, speed limits, and U.S. Geological Survey elevation data, their analysis focused on roads with speed limits of 45 mph (72 kph) and higher. They discovered that over 43% of the studied trips involved at least one instance of speeding, with drivers spending nearly 12% of their time exceeding the limit.
The study found that if drivers of light-duty, conventional internal combustion engine vehicles consistently drove at posted speed limits, it could lead to an average daily saving of $22 million (based on fuel costs at the time), conserve 6.7 million gallons of fuel, and reduce carbon dioxide emissions by 57,000 metric tonnes. This environmental benefit is comparable to removing approximately 5.5 million passenger vehicles from the road.
Despite the common perception that speeding saves valuable time, the researchers concluded this is largely untrue. For an average daily driving distance of 28.6 miles (46.03 kilometers), driving at or below the posted limit would only extend the journey by about 54 seconds per day.
William Northrop, a mechanical engineering professor at the University of Minnesota and study co-author, commented on the trade-off: “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.” The research also indicated that driving slower is beneficial for battery-electric vehicles, based on California modeling.
Interestingly, the study highlighted regional differences in driving behavior. Nevada showed both high speeding prevalence and significant speed excess. Florida, Georgia, and North Carolina exhibited high speeding prevalence, though not necessarily high speed excess. Conversely, Montana, Wyoming, Idaho, and South Dakota demonstrated low speeding prevalence and speed excess.
Driving faster increases a vehicle’s energy use and the emissions from its engine, as well as 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 55 mph national speed limits 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 to volatile gas prices as the war in Iran has sent the cost for a gallon of fuel above $4 this year. Experts have said there are a number of ways to improve one’s gas mileage, including something as simple as slowing down. Less fuel needing to be purchased because of better 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 from driving more slowly still only represents a fraction of daily gasoline consumption in the U.S., which is about 375 million gallons daily.
“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.”
