Lifetime Modeling of Deficient Bridges in New York

Levi Phippen, Utah State University


Given the importance of bridges to a state's economy and strength, and the costs involved in building and maintaining bridges, maximizing their service life is essential. In order to safely extend a bridge's utility as long as possible, an understanding of its lifetime processes is needed. This paper attempts to model the lifetime of a bridge in New York once it has become deficient. Lifetime is defined to be the length of time between deficiency classification and failure. A bridge is considered deficient when certain structural components receive a poor rating in the National Bridge Inventory, which is compiled annually by the Federal Highway Administration. A list of bridge failures is provided by the New York State Department of Transportation.

In 2012 the Federal Highway Administration database showed that 39.5 percent of New York's bridges were deficient. Using analysis of variance and considering a bridge failure to be a random Bernoulli trial, this paper shows that New York's deficient bridges are typically older than their non-deficient counterparts, and that they are also more susceptible to failure. From survival analysis techniques an estimate of the mean time to failure of a deficient bridge is found to be 47.2 years. Finally, a statistical model is created to predict the lifetime of a deficient bridge, while accounting for influential factors such as average daily truck traffic, deck geometry and structural evaluation ratings.