A Retro-Analysis of I-40 Bridge Collapse on Freight Movement in the U.S. Highway Network using GIS and Assignment Models

Abstract

Bridges are critical but vulnerable elements of a highway transportation system. A bridge collapse not only affects the freight movement on the bridge but also the flow in the entire network, posing negative impacts on local, regional, and national economy. This study examines the spatial and economic impact of the 2002 I-40 Bridge collapse in Oklahoma on freight flow movement in the U.S. highway network. Freight Analysis Framework (FAF) databases, TransCADTM software, and two assignment models (All-or-Nothing and User Equilibrium) are used to analyze the freight flow changes before and after the bridge collapse along with two different freight assignment approaches. The first approach assigns the origin-destination freight flow to the network with the collapsed bridge removed. The second involves two successive assignments - first by excluding the pre-hazard freight flow on the bridge and assigning the rest of the flow to the post-disaster network, and second, by assigning the freight flow on the bridge in pre-disaster conditions to the post-disaster-network. The research showed that the bridge collapse did not only impact the freight flows on nearby highway network links, but also affected flows on links further away from the bridge. This finding casts doubts on the conventional models relying on gravity-based spatial distance decay effects, which often overestimate the nearby but underestimate the further-out freight flow changes in the network.