A nationwide study by researchers at the University of Minnesota Twin Cities reveals that adherence to posted speed limits could dramatically curb U.S. fuel consumption and greenhouse gas emissions, saving Americans billions of dollars annually while adding less than a minute to the average daily commute.
The paper was recently published in Communications Sustainability, a peer-reviewed journal.
Researchers analyzed over 120 million real-world vehicle trips across the United States, showing that if drivers complied with posted speed limits, it could save an average of $22 million, 6.7 million gallons of fuel and 57,000 metric tonnes of carbon dioxide every single day for light-duty engine-powered vehicles — which account for 14.6% of total energy consumption in the country.
"We already understand the physics of how speed affects fuel consumption, but quantifying the exact magnitude of those savings at a national scale gives us a clearer picture of the actual impact," said Bharat Jayaprakash, Ph.D. student in the Department of Mechanical Engineering at the University of Minnesota and lead author on the paper.
Previous transportation research relied on localized, small-scale samples or general assumptions about fuel economy based on laboratory tests. This project marks a major milestone in transportation science. With volatile fuel prices and uncertainty about the expansion of electric vehicles in the marketplace, the study shows that changing driver behavior offers an immediate, cost-effective tool for reducing fuel use and emissions.
The researchers were able to review a large amount of data including driving data on U.S. road networks, speed limits and elevation data from the U.S. Geological Survey. They then calibrated multiple, vehicle specific energy-consumption models using advanced vehicle dynamics software developed by the National Laboratory of the Rockies, formerly known as the National Renewable Energy Laboratory.
"While internal combustion engine-powered vehicles have become significantly more efficient in the past decades, they have also become much more powerful. Driving fast is easier than ever," said William Northrop, University of Minnesota mechanical engineering professor and corresponding author on the paper. "Our study examines an obvious yet difficult-to-implement intervention for major fuel savings that can be achieved without replacing our cars: driving slower."
The researchers noted that more work is needed to fully understand the impact of driving on fuel and emissions.
"Key remaining challenges of our research are to expand our framework to more diverse roadways and understand the impacts of aggressive accelerations on fuel use and emissions," added Northrop. "Exploring both speed and acceleration reductions will give us an even more complete picture of real-world fuel savings potential."
Future phases of the project will utilize an instrumented electric vehicle equipped with multi-sensor perception systems to capture micro-scale driving behavior in real time. Sponsored by the Minnesota Department of Transportation's Local Road Research Board, current research focuses on collecting high-fidelity, real-world drive cycles to precisely model how micro-scale driving habits impact energy consumption and emissions at the fleet level.
The research was partially supported by the National Science Foundation.
Read the entire paper, entitled "Speeding incurs substantial environmental and economic costs nationwide for negligible travel time savings, on the Nature website.
