Drivers who exceed posted speed limits on U.S. roads waste money on fuel and contribute to harmful emissions, with little to no time saved, according to new research. The study suggests that adhering to speed limits could save millions of dollars and millions of gallons of fuel each day.
University of Minnesota researchers analyzed 120 million vehicle trips across the United States using driving data, speed limits, and elevation data. The analysis, which focused on roads with speed limits of 45 mph and higher, found that over 43% of the trips involved speeding, and drivers spent nearly 12% of their driving time exceeding the speed limit.
If drivers of conventional internal combustion engine vehicles adhered to posted speed limits, it could save approximately $22 million daily based on fuel costs at the time, along with 6.7 million gallons of fuel and 57,000 metric tons of carbon dioxide. The researchers stated this reduction in emissions is comparable to taking about 5.5 million passenger vehicles off the road.
Despite the common perception that speeding saves time, the study found that for an average daily driving distance of 28.6 miles, driving at or below the speed limit adds only about 54 seconds to the total travel time. William Northrop, a mechanical engineering professor at the University of Minnesota and study co-author, noted that if the primary goal is to save time, speeding might seem beneficial, but if the objective is safety and fuel conservation, driving slower is the better option.
The research also briefly considered battery-electric vehicles, finding that slower driving is also beneficial for their efficiency. The study observed state-level variations, with Nevada showing high speeding prevalence and speed excess, while states like Florida, Georgia, and North Carolina had high speeding prevalence but not necessarily high speed excess. Montana, Wyoming, Idaho, and South Dakota demonstrated both low speeding prevalence and speed excess.
Driving faster increases a vehicle's energy consumption and emissions, while reducing efficiency. Although engines have become more efficient over decades, speed limits have also increased since the 1970s energy crisis, which mandated a national 55 mph speed limit. Accounting for current average gas prices and increased vehicle miles traveled, the potential daily savings for Americans could rise to approximately $26 million and 7.2 million gallons of fuel.
Experts note that while these savings are significant, the fuel saved from slower driving represents a fraction of the total daily gasoline consumption in the U.S., which is around 375 million gallons. However, the study highlights that slowing down is a readily available method for drivers to conserve fuel and reduce environmental impact, especially as U.S. drivers remain sensitive to volatile gas prices.