Cars: Why Lawns Save Little Time and Cost a Lot of Fuel

In the United States, speeding during daily commutes appears to offer little time savings while significantly increasing fuel consumption and emissions, according to a new study analyzing 120 million trips. The research, published in Communications Sustainability, reveals that adhering strictly to speed limits could save millions of gallons of gasoline annually and reduce carbon dioxide emissions equivalent to removing nearly six million vehicles from roads. Conducted over four Wednesdays in 2021, the study used data from national road networks, posted speed limits, and elevation information from the U.S. Geological Survey to assess driving patterns across the country. The findings show that more than 43 percent of the analyzed trips included at least one instance of speeding. On average, drivers spent approximately 12 percent of their travel time above the legal limit. Despite common perceptions that faster driving saves time, the study found that maintaining speeds within legal limits results in only about 54 seconds of additional travel time per day for the average driver. This suggests that the perceived time benefits of speeding are minimal compared to the increased fuel costs and environmental impact. Researchers from the University of Minnesota in Minneapolis calculated that if all drivers adhered to posted speed limits, the nation could save up to $22 million per day in fuel costs, equivalent to roughly €20 million. These figures were based on historical fuel prices and applied to the entire population. Additionally, the study estimates that slowing down would prevent the consumption of around 6.7 million gallons (approximately 25.4 million liters) of gasoline each year and cut carbon dioxide emissions by about 57,000 tons. That reduction is comparable to taking nearly five and a half million cars off the road. The researchers emphasize that these savings apply to the broader population when considering fuel and emission reductions, while individual time gains remain negligible. For example, with an average daily commute of 28.6 miles (about 46 kilometers), sticking to speed limits adds just over a minute to travel time. This underscores how small adjustments in driving behavior can lead to substantial nationwide benefits, even though they have minimal personal impact. Dr. Bharat Jayaprakash, a graduate student at the University of Minnesota’s Department of Mechanical Engineering and lead author of the study, explained that while the physics behind speed affecting fuel efficiency was already known, quantifying these effects on a national scale provides clearer insights into real-world impacts. “We knew the relationship between speed and fuel consumption, but seeing the exact magnitude of savings on a large scale gives us a better understanding of the actual effect,” he stated in a press release. Rob Middleton, an adjunct research scientist at the University of Michigan’s Department of Mechanical Engineering who was not involved in the study, praised the research as well-conducted. However, he noted that the amount of fuel saved through slower driving represents only a fraction of the country’s total daily gasoline consumption. With the U.S. using approximately 375 million gallons of gasoline per day, around 1.4 billion liters, the savings from reduced speeding account for less than 2 percent of this figure. “It’s a big number, but it’s still just a small part of the overall picture,” Middleton remarked. As policymakers and transportation authorities consider strategies to improve fuel efficiency and reduce emissions, this study highlights the potential benefits of stricter enforcement of speed limits. While individual drivers may not notice significant changes in their travel times, the cumulative effect of widespread compliance could yield major economic and environmental advantages. The research also raises questions about public awareness of the true cost of speeding, both in terms of financial expenditure and ecological consequences.