On May 26, 1989, a pile bent and a two-span segment of the temporary bridge that carries Harrison Road over the Great Miami River collapsed. A passenger car fell into the river, causing the drowning of two occupants. Numerous sources confirm that the river, which was in high flood, carried a large amount of debris of various sizes and configurations. According to witnesses' statements, floating debris struck the pile bent, causing it to fail suddenly, bringing with it two sections of the superstructure. A study was commissioned by the National Transportation Safety Board (a) to provide a detailed analysis of the causes and sequence of failure of the structural elements contained within the temporary pile bent and superstructure;(b) to conduct an in-depth review of alternate analyses used to ascertain the causes of failure;(c) to provide recommendations as to the procedural issues which have surfaced due to the failure; and (d) to provide an evaluation of the pile bent with respect to conformance to the AASHTO Standard Specifications for Highway Bridges. The results of the study identify various factors that influenced the failure of the pile bent. These include the lack of quantitative guidelines under AASHTO for the determination of frequency and size of floating debris, variances allowed for the design and construction of temporary bridge structures, design procedures for determination of dynamically applied debris forces, and the rating of pile bents under hydrostatic, debris, and line-loading conditions.