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A regional bridge failure database was used to determine the bridge failure rate with associated causes. Using a sample population from one DOT over a 25-year period, the average number of bridge failures was approximately 1/4,700 annually with a 95% confidence interval from 1/6,900 to 1/2,700 annually. The number of bridge failures per year was modeled with a geometric distribution that requires a constant failure rate. Based on a validation analysis with bridge failures from six separate DOTs, other DOTs have bridge failure rates within the determined sample population 95% confidence interval. Analysis of the failed bridges by year of construction shows no apparent era of construction that is more susceptible than another to failure. Correspondingly, the determined constant failure rate ascertained in the model selection indicates that the changes in bridge design specifications and maintenance regulations do not appear to have significantly reduced bridge failure rates. Based on the data extrapolation, the estimated average annual bridge failure rate in the United States is between 87 and 222 with an expected value of 128.
Cook et al. (Sat,) studied this question.