Research Reports

Traffic Flow and Road User Impacts of the Collapse of the I-35W Bridge over the Mississippi River

Principal Investigator:

Shanjiang Zhu, David M Levinson, Henry Liu, Kathleen A Harder, Adam Danczyk

July 2010

Report no. Mn/DOT 2010-21

Projects: Traffic Flow and Road User Impacts of the Collapse of the I-35W Bridge over the Mississippi River

Topics: Data and modeling

Major network disruptions have significant impacts on local travelers. A good understanding of behavioral reactions to such incidents is crucial for traffic mitigation, management, and planning. Existing research on such topics is limited. The collapse of the I-35W Mississippi River Bridge (August 1, 2007) abruptly disrupted habitual routes of about 14,000 daily trips and forced even more travelers to adapt their travel pattern to evolving network conditions. The opening of the replacement bridge on November 18, 2008 generated another disturbance (this time predictable) on the network. Such "natural" experiments provide unique opportunities for behavioral studies. This study focuses on the traffic and behavioral reactions to both bridge collapse and bridge reopening and contributes to general knowledge by identifying unique patterns following different events. Three types of data collection efforts have been conducted during the appropriate frame of reference (i.e. before vs. after bridge reconstruction): 1) GPS tracking data and associated user surveys, 2) paper and internet-based survey data gauging travel behavior in the post-bridge reconstruction phase, and 3) aggregate data relating to freeway and arterial traffic flows, traffic control, and transit ridership. Differences in reactions to planned versus unplanned events were revealed. Changes in travel cost were evaluated and their temporal and spatial patterns were analyzed. This report concludes with thorough discussions of findings from this study and policy implications.

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