PSU Graduate Researcher Huajie Yang Explores Light Rail's Impacts on Ridership and Congestion

A TriMet MAX light rail train passes in front of a sidewalk with guardrails

Dr. Huajie Yang, who graduated in 2020 with a PhD in Urban Studies and Planning from Portland State University, devoted his doctoral research to studying the impacts of light rail transit. His dissertation, "Short-term and Long-term Effects of New Light Rail Transit Service on Transit Ridership and Traffic Congestion at Two Geographical Levels," quantitatively examines the effect of new Light Rail Transit (LRT) services on transit ridership and traffic congestion over time.

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Yang examined these impacts at two different geographic levels. At the corridor level, he conducted case studies of two light rail lines in the Portland, Oregon region (TriMet's Green and Orange MAX lines). At the regional level, he used a synthetic control method to construct a "synthetic" control Urbanized Area that closely approximates the counterfactual transit ridership and traffic congestion scenario - in the absence of light rail projects - in three urbanized areas across America.

The results of the corridor-level study suggest that both the Green and Orange lines increased transit ridership in the short- and long-term, and relieved traffic congestion in the short-term, while having no statistically significant effect on traffic congestion in the long-term, likely due to induced traffic demand. Results of the regional-level study suggest that, while new light rail transit services contributed to transit ridership in most urban areas, they did relieve traffic congestion in a limited number of urban areas, and that the effect changed over time and varied across places. The comprehensively temporal and geographical analysis will provide a better understanding of the impacts of new light rail transit services on transit ridership and traffic congestion, and hence provides policy makers insightful suggestions for building light rail projects to be more sustainable and to more effectively attract riders from former automobile drivers.

Photo courtesy of TriMet

The Transportation Research and Education Center (TREC) at Portland State University is home to the National Institute for Transportation and Communities (NITC), the Initiative for Bicycle and Pedestrian Innovation (IBPI), and other transportation programs. TREC produces research and tools for transportation decision makers, develops K-12 curriculum to expand the diversity and capacity of the workforce, and engages students and professionals through education.

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