Researchers assess performance of state transportation systems using sustainability index

By Chris McCahill

New research from the University of Connecticut sheds valuable light on key policy objectives for improving the sustainability of state transportation systems. The research was just published in a special issue of Research in Transportation Business and Management and featured in UConn Today. According to the research, states with high rates of automobile use and high VMT are generally ranked poorly.

Researchers from the departments of civil engineering and geography set out to develop a framework for towns, cities, states, and nations to assess how their transportation systems affect their long-term sustainability. Their product, the Transportation Index for Sustainable Places, is designed to account for not only the environmental impacts of different systems, but also the economic and social impacts.

The researchers evaluated the TISP using data for each of the fifty states, revealing a wide range in variation attributable to factors such as land use patterns, automobile use, and transportation funding sources. Although the TISP incorporates nearly two-dozen variables, the researchers focused on a few key indicator variables to explain the variation among different types of transportation systems.

Regarding environmental sustainability, the study shows that per capita carbon emissions vary by a factor of six among the states. The researchers considered both government and household spending to explain economic impacts. Government spending on roads and transit ranges from roughly $300 to $1,300 per capita, while household transportation spending ranges from approximately 20% to more than 40% of household income. To capture some of the social impacts, the researchers assessed fatality rates, shown in Figure 1, which range from 5 to 25 annual traffic deaths per 100,000 people. In each case, the variation is explained in large part by differences in vehicle miles of travel (VMT) per capita—an indicator of how automobile-oriented each state’s transportation system is overall.

Figure 1. Traffic fatality rates versus VMT per capita (source: Garceau et al. 2013)

Figure 1. Traffic fatality rates versus VMT per capita (source: Garceau et al. 2013)

This work is an important step toward enabling policy makers and transportation agencies to focus on a wider range of outcomes than traffic mobility and congestion relief. For example, the researchers found that—along with the more obvious environmental benefits—investments in transit, bike, and pedestrian infrastructure offer considerable system-wide cost savings. “At the state level, it’s cheaper per person to build and maintain diverse transportation systems,” explained Timothy Garceau to UConn Today.

The researchers hope this work will help shift focus away from conventional transportation planning measures, such as the travel-time index, which they say poorly reflect the needs of those who travel short distances or do not drive—a majority of the population in some cities.  The TISP serves as a new tool for decision makers to compare their performance against their peers and build more sustainable systems that benefit all users.

Chris McCahill is a Senior Associate at SSTI.