United States Department of Transportation
i
Transportation Infrastructure Robustness : Joint Engineering and Economic Analysis
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2017-11-01
[PDF-2.64 MB]
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Abstract:The objectives of this study are to develop a methodology for assessing the robustness of transportation infrastructure facilities and assess the effect of damage to such facilities on travel demand and the facilities users’ welfare. The robustness of transportation facilities is related to two types of damage: a) longitudinal deterioration in facility engineering quality; and b) sudden shock due to unexpected extreme events. This study focuses on the first determinant and its economic implications. Achieving the stated objectives requires reviewing the basic principles of infrastructure durability, modeling the relation between travel demand and infrastructure damage, and analyzing users’ economic welfare. Economic welfare is expressed in terms of Consumer Surplus (CS) which is defined as the difference between what users of a transportation facility are willing to pay in terms of travel time and associated direct costs such as the cost of fuel and what they actually spend. When deterioration occurs in one facility within the network, the equilibrium travel time and associated costs on this facility will increase and thus travelers’ CS will drop.
To illustrate the proposed analysis procedure, this study implements the basic concepts using a numerical example that assesses the robustness of an infrastructure system consisting of a two-bridge network comprising the Whitestone Bridge and the Throgs Neck Bridge that connect the boroughs of Queens and the Bronx of New York City. The two bridges are found to be substitute facilities as the total traffic on the combined network remains essentially constant. Peak traffic volume on each facility was found to be directly related to the condition of the bridge deck riding surface. The condition of the deck surface is expressed by the Deck Condition Rating (DCR) reported by bridge inspectors.
As the deck surface condition deteriorates and DCR decreases, peak traffic volume on the deteriorating facility also decreases while traffic volume on the substitute facility increases. These changes in peak traffic volumes and riding surface conditions increase travel time on both facilities leading to higher users costs.
The results of the analysis show that when the DCR of one of the two facilities composing the network decreases by 1% from its best condition, the facility consumer’s surplus decreases by 2.41% due to preventing some users from using the facility. At the same time, the consumer surplus of the substitute facility will also decrease by 5.91% due to the congestion resulting from the additional users who migrate from the deteriorated facility. The consumer surplus of the entire network will diminish by 2.47 %. Where a drop of one level on the 1-7 condition rating scale used by New York State represents a 14% decrease in DCR.
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