On November 19, 1991, an unusual series of events led to a train derailment and bridge collapse in Shepardsville, Kentucky. The insurer for the train company retained Exponent to investigate the causes and circumstances surrounding the incident. Within 36 hours of the accident, an Exponent investigative team arrived in Kentucky to survey the site.
Exponent determined that a garbage truck became stuck under a railroad overpass when the driver decided to take a shortcut. The impact of the truck into the overpass pushed the rails out of alignment. When a train crossed the overpass a few minutes later, the lightest cars on the train derailed.
Just beyond the overpass, the train approached a three-span trestle bridge. Realizing that some of the cars had derailed, the train engineer hit the brakes, which caused the derailed cars to jackknife. As the cars lost control, they slammed into the sides of the trestle bridge. The engineer managed to cross the bridge with a few cars while the rest of the train and the bridge collapsed behind him. Hazardous materials that the train had been transporting were dumped into the river, resulting in the evacuation of about 2000 people.
Elements of Exponent’s investigation included calculating the truck’s speed at the time of impact with the overpass, evaluating signage for the overpass; assessing the design of the overpass and the rails, studying train dynamics and the mechanics of derailment, and analyzing the design and construction of the bridge.