Green accessibility: Estimating the environmental costs of network-time prisms

Network-time prisms are powerful measures of space-time accessibility within transportation networks.  However, they fail to capture the environmental costs of potential mobility.  In this paper, we present a method for estimating the expected energy consumption and emissions associated with network time prisms.  We also verify our method using data from instrumented vehicles moving within an experimental network-time prism in the Phoenix AZ road network.

Song, Y., Miller, H.J., Stempihar, J. and Zhou, X. (2017), “Green accessibility: Estimating the environmental costs of network-time prisms for sustainable transportation planning,” Journal of Transport Geography, 64, 109-119.

Abstract.  Accessibility, or the ease to participate in activities and obtain resources in a given environment, is crucial for evaluating transportation systems. Greater accessibility is often achieved by increasing individuals’ potential mobility. However, potential mobility, if realized by motorized modes, can also generate negative environmental impacts such as fossil fuel consumption and greenhouse gas (GHG) emissions. While the negative environmental impacts of greater mobility are acknowledged, there has been a lack of research to validate those impacts using empirical data, especially considering variations in individuals’ mobility levels. This paper presents a method for estimating the expected environmental costs of accessibility represented by a network-time prism (NTP). A NTP delimits all accessible locations within a network and the available time for an individual to present at each location given a scheduled trip origin and destination, a time budget and the maximum achievable speeds along network edges. Estimating the expected environmental costs of a NTP involves three steps: (1) semi-Markov techniques to simulate the probabilities to move along network edges at given times; (2) the speed profiles for reachable edges, and (3) a cost function that translates speeds into environmental impacts. We focus on air quality and employ the motor vehicle emission simulator MOVESLite to estimate the CO2 emissions at both the edge and prism levels. We calibrate and validate the methods for experimental NTPs defined within the Phoenix, AZ, USA road and highway network using vehicles instrumented with GPS-enabled onboard diagnostic devices (OBD). We demonstrate the effectiveness of our method through two scenarios and investigate the impact of changes in mobility levels on the expected CO2 emissions associated with the experimental NTPs.

Keywords: Space-time accessibility; Network-time prism; Emissions

Out for Good podcast on Mobility in Columbus

I am happy to be part of the first episode of Out for Good, a weekly podcast that explores issues facing Central Ohio and highlights the individuals and organizations making an impact.

Elissa Scheider (Transit Columbus) and I discuss why mobility is important to our community with co-hosts Jason Phillips and J.M. Rayburn.  You can listen to the podcast here.

“Gridlock Sam” Schwartz to speak at Ohio State on September 20th

The Center for Urban and Regional Analysis (CURA) is pleased to welcome Samuel Schwartz to Ohio State University for a free public lecture on Tuesday, September 20, 2016, 4:00pm at the Wexner Center Film/Video Theater, 1871 N. High Street, Columbus, OH 43210

Sam Schwartz is the most famous traffic engineer in the world, serving as New York City Transportation Commissioner under several mayors, and now leads an international and highly influential consulting firm, Sam Schwartz Engineering.  Mr. Schwartz invented the word ‘gridlock,’ earning the enduring moniker “Gridlock Sam.”

Sam is called the “Jane Jacobs of Traffic” due to his long fight to create room for humans and social space in city streets and an “urban alchemist” for his uncanny ability to grow green space from asphalt.  In Canada, is he known as “[The] Wayne Gretzky of Traffic Planning.”

Gridlock Sam will speak about his recent book, Street Smart: The Rise of Cities and Fall of Carsa lively history and discussion of how to move cities beyond automobile dominance.

The lecture is free and open to the public, but space is limited, so RSVP today at:

More information about Sam Schwartz

CURA Gridlock Sam