Simply driving at the posted speed limit could save Americans billions of dollars in fuel costs while cutting greenhouse gas emissions, according to a new study from researchers at the University of Minnesota Twin Cities.
The study, published in Communications Sustainability, found that slowing down to legal speed limits could have a surprisingly large impact across the United States.
Researchers estimate that if drivers followed posted speed limits, the country could save about 6.7 million gallons (25 million liters) of fuel every day.
That would also reduce carbon dioxide emissions by around 57,000 metric tons daily and save drivers roughly $22 million in fuel costs each day.
These findings apply to light-duty gasoline and diesel vehicles, such as passenger cars, SUVs, and pickup trucks, which account for about 14.6% of total U.S. energy use.
Lead author Bharat Jayaprakash, a doctoral student in the Department of Mechanical Engineering at the University of Minnesota, said scientists have long understood that higher speeds increase fuel consumption.
However, this study is one of the first to estimate just how much money and fuel could be saved across the entire country if people simply drove within the speed limit.
To reach their conclusions, the researchers analyzed more than 120 million real-world vehicle trips from across the United States.
They combined this information with detailed road maps, speed limit data, and elevation information from the U.S. Geological Survey. They also used advanced computer models to calculate how different driving speeds affect fuel use under real driving conditions.
One important finding was that slowing down would have only a very small impact on travel times. For the average driver, obeying speed limits would add less than one minute to a typical daily commute. In return, drivers would use less fuel, spend less money, and produce fewer emissions.
Professor William Northrop, the study’s corresponding author, noted that while modern gasoline-powered vehicles have become much more fuel-efficient over the years, they have also become far more powerful. As a result, it is easier than ever for drivers to travel well above the speed limit, even though doing so burns more fuel.
The researchers say reducing speed is one of the simplest ways to improve fuel efficiency without requiring people to buy new vehicles or wait for electric cars to become more common. At a time when fuel prices can change quickly and the transition to electric vehicles is still ongoing, changing driving habits may offer an immediate and inexpensive way to reduce fuel use and emissions.
The team plans to continue the research by looking beyond speed alone. Future studies will examine how hard acceleration and other driving habits affect fuel consumption and pollution. They also plan to collect detailed driving data using specially equipped electric vehicles to better understand how everyday driving behavior influences energy use and emissions on a national scale.
The researchers believe that combining smoother driving with lower speeds could reveal even greater opportunities to save fuel, reduce costs, and lower greenhouse gas emissions.
