Drivers could save millions of gallons of fuel and tens of millions of dollars every day if they simply obeyed posted speed limits, according to a new study published in the journal Communications Sustainability.
Researchers from the University of Minnesota analyzed more than 120 million real-world vehicle trips across the United States and found that strict compliance with speed limits would save an average of 6.7 million gallons of gasoline, $22 million in fuel costs and 57,000 tonnes of carbon dioxide emissions per day. The emissions reduction is equivalent to removing about 5.5 million passenger vehicles from the road annually.
The findings highlighted an imbalance between the cost of speeding and its benefit. The study found that drivers who consistently followed posted speed limits would add only about 54 seconds to their daily travel time, or roughly six minutes per week on average.
Researchers also examined a more efficient driving approach that combined speed-limit compliance with gradual deceleration and coasting, rather than maintaining speed and braking aggressively at the last moment. Under that scenario, daily savings increased to approximately 8.2 million gallons of fuel, $27 million in fuel costs and 69,000 tonnes of CO2 emissions.
The study found speeding remains common. About 43.2 per cent of trips included at least one speeding event, with speeding drivers exceeding the posted limit by an average maximum of 11.2 mph. Those drivers spent nearly 12 per cent of their trip time above the speed limit.
According to the researchers, the fuel penalty associated with speeding is substantial because aerodynamic drag increases rapidly as vehicle speeds rise, making high-speed driving disproportionately less efficient. Even relatively small increases in cruising speed can have a significant impact on fuel consumption.
The analysis suggests that nationwide compliance with speed limits would save roughly 2.4 billion gallons of gasoline annually. Researchers estimate those savings would be comparable to the annual fuel consumption of millions of passenger vehicles.
The study’s authors argue that the commonly cited justification for speeding, saving time, largely disappears when analyzed across a driver’s entire day. While individual drivers may perceive a meaningful benefit from exceeding the speed limit, the actual reduction in travel time was found to be minimal compared with the fuel consumed and emissions generated.
The researchers also noted that speeding carries broader societal costs beyond fuel consumption, including safety impacts. However, the primary focus of the research was the relationship between speed, energy use, consumer costs and emissions.
One limitation acknowledged in the report is that it does not account for how traffic conditions might change if a large percentage of drivers suddenly began obeying speed limits. The analysis focused on the direct effects of driver behaviour rather than broader traffic-flow impacts.
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