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Pump the brakes: Rough roads reduce traffic speeds and safety, based on WVU research

Corner of a highway

I68 feature: New research based on transportation data by WVU economists Brad Humphreys and Alexander Cardazzi shows that rough roads reduce traffic speeds and safety. (WVU Photo/Jennifer Shephard)

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Rough roads and decreasing pavement quality drive up vehicle crash rates and slow down average vehicle speeds, posing major concerns for motorists and highlighting the importance of public transportation spending, West Virginia University economists have concluded.

Brad Humphreys and Alexander Cardazzi, both of the John Chambers College of Business and Economics, found that maintaining smooth roads may lead to increased traffic speeds and decreased crash rates. 

Their study, published by the National Bureau of Economic Research, was funded through an interagency agreement between the U.S. Department of Transportation and the National Science Foundation.

“Essentially, we found that rougher roads really impact speed and traffic safety in negative ways, much more so than previously thought,” Cardazzi said.

“If you let the pavement quality deteriorate, it turns it into more of a danger in that road segment in terms of crash rates,” Humphreys said. “We should be concerned about how our road quality is making people travel slower and more likely to have accidents.”

This research provided important evidence on the relationship between highway roughness and traffic outcomes using data from Federal-Aid Highway System roads in California from 2011 to 2019. FAHS roads include interstate highways and U.S. routes.

Data from FAHS showed statistically and economically significant increases in vehicle crash rates and decreases in average vehicle speed caused by road damage. These impacts imply significant increases in social costs attributable to road damage.

Humphreys said that the state of California was chosen for research because high quality data are available for both the quality of the roads and traffic outcomes.

“In California, you have the beach, you have the snow up north, you have the more mountainous places in the east, and you have the desert down south,” Cardazzi said. “There's all sorts of really good geographic variation that we can take advantage of and see how different climates impact this smoothness." 

Humphreys added that California also has large cities and rural areas, which is beneficial because there’s more opportunity to test a variety of different roads. 

This research translates directly to roads in West Virginia.

“These results are probably magnified in West Virginia because our roads are, on average, much rougher or much lower quality than anywhere in California,” Humphreys said.

Their findings also reveal significant social costs, in the form of reduced traffic safety, increased vehicle operating costs and longer travel times. These costs underscore the need for changes in current transportation infrastructure investment policies, they said.

Humphreys said that there is a benefit to road maintenance and the results of this study help inform decisions to interrupt traffic flow on highways and interstates to improve pavement quality. 

“People are going to be able to drive at higher speeds,” Humphreys said. “They can get to where they’re going faster along that stretch of interstate and there's going to be fewer crashes because of that maintenance. It's costly to slow people down and not let them be able to drive at highway speeds. Accidents are really costly and so that should help us to place those huge maintenance projects in an economic context.”

Humphreys said that currently the United States is debating a $1 trillion infrastructure bill, much of it directed to road improvement.

“Our research really provides important justification for why we might want to spend a trillion dollars or hundreds of billions of dollars improving road quality, because we generate important evidence that society will benefit from that,” Humphreys said. “With that debate going on, I think it's important to have really solid evidence like the evidence we've generated in this paper, that is worthwhile.”

Citation: Where the Rubber Meets the Road: Pavement Damage Reduces Traffic Safety and Speed



CONTACT: Jake Stump
WVU Research Communications

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