Bridges, roads, bike lanes, traffic signals, railroads and interstate highways allow millions of people to travel each year, but they are one of the most expensive investments for governments and taxpayers, according to a group of civil and environmental engineering researchers at Penn State.
In a partnership with the Pennsylvania Department of Transportation (PennDOT), researchers examined development across Pennsylvania's 67 counties, statistically modeling how each county's transportation infrastructure impacted the economic health of the region and beyond. The team published their findings in the International Journal of Transportation Science and Technology.
"Although there is a general understanding that investments in transportation infrastructure have an impact on the economic development of an area, it's always been hard to quantify," said Vikash Gayah, professor of civil and environmental engineering, interim director of the Larson Transportation Institute and a co-author of the paper. "The models we developed through this study help us showcase the impact that infrastructure like bridges and traffic signals have on not just a specific region, but the surrounding counties as well."
Researchers used four broad categories of data to develop four models on the impact of infrastructure investments: economic performance indicators, such as the income and employment levels of an area's population; socio-demographic indicators, such as the average age of workers and their family size; transportation investments, such as improvements to bridges and roads; and existing transportation infrastructure usage.
The team found that bridges have the highest county-specific impact of all investments: Increasing the bridge count in a county by just 1% can lead to more than a 0.08% increase in gross domestic product in that county. When looking at the impacts on neighboring counties, the researchers said that investments in roads and traffic safety infrastructure like traffic signals had the greatest economic improvement.
In their models, researchers examined the impacts of spatial spillover, which occurs when the economic effects following transportation infrastructure investments in one area influence the economy of a neighboring region, according to Ilgin Guler, associate professor of civil and environmental engineering and co-author of the paper. Spillover can be classified as either positive or negative. Investments that benefit neighboring counties' economic function are positive, while investments that hinder economic function are negative. For example, Guler explained how installing traffic signals in one county had a positive impact on the gross domestic product of neighboring counties as well, even if those counties did not receive a similar infrastructure investment.
"Our goal with this research was to examine how investments in transportation infrastructure influence the economic activity of the local communities surrounding the investments," Guler said. "Specifically, we wanted to create a model that clearly accounts for spatial spillover between counties when calculating the impact of an infrastructure development in an area."
Additionally, the team defined the "spatial dependence" between counties when analyzing the data. Prior research had classified neighboring counties based on distance alone. To accurately showcase the effects of investments between counties, the team considered additional variables, including proximity to population centers and interstate highway connections located within the county receiving the investment, to better define a neighboring county.
"The more variables in our data, the better we can develop and adjust our model to present an accurate picture of the economic impacts a region would see following an investment," Guler said. "When you're looking at the impact of major infrastructure investments like roads and bridges, smaller counties saw the largest improvement in their economic performance. Similar investments in bigger counties saw returns as well, but they were lower relative to the economic size of the smaller counties."
