Assessing the potential for rail-truck intermodal transportation to reduce tractor-trailer accidents on Tennessee highways

In recent years, the movement of long-haul domestic freight by rail-truck intermodal has received considerable attention. One of the perceived societal advantages of rail-truck intermodal transportation relative to over-the-road truck service is improved highway safety. The argument is that when the line-haul portion of an over-the-road truck movement is replaced by rail transportation, tractor-trailer exposure levels on the highway system will be lessened. The decrease in exposure should then result in a reduction in the number of tractor-trailer accidents occurring on the highway system.

This study focuses on the highway safety aspects of intermodal. In particular, the study attempts to measure how many tractor-trailer accidents occur in Tennessee for which rail-truck intermodal transportation could have been used to haul the freight instead. By assigning dollar values to these accidents according to their injury outcome, some estimate of the accident savings can be achieved. Also of interest is measuring the effect that various changes in the rail and/or truck industry might have on the number of tractor-trailer accidents in Tennessee. For example, new intermodal technology aimed at capturing shorter-haul markets would likely reduce the number of trucks operating in such markets, and also reduce accident occurrence. Finally, the safety benefits are assessed to determine whether the Tennessee state government should encourage, within their limits, a shift toward intermodal, and if so, what specific actions can be taken.

A decision model was developed for determining whether a shipment in truck carriage is suitable for intermodal transport. The model included such factors as type of commodity to be transported, shipment origin and destination, line-haul characteristics, and total length of haul. The data used to apply the model were information recorded on the shipping papers carried by each tractor-trailer driver who became involved in an accident in Tennessee. These papers document the type of cargo being transported as well as its origin and destination. The percentage of truck movements that were determined to have a potential for intermodal transport, based on the information provided on the shipping papers, represented the accident reduction.

The results of this study indicated that approximately one out of every four tractor- trailer accidents occurring on Tennessee highways involved movement of a commodity over a distance that was suitable for intermodal. The annual cost of these accidents was estimated at $21 million to $29 million.

There is significant potential for advancements in intermodal technology and other factors to further reduce tractor-trailer accident occurrences. Currently, intermodal is cost competitive with over-the-road trucks at trip distances of about 750 miles. The analysis indicated that for every 100 mile reduction in this distance threshold, roughly, about a 5 percent decrease in the number of tractor-trailer accidents is possible (assuming that smaller markets do not grow appreciably).

Even though intermodal transportation represents interstate commerce, the state government still can and should play a role in bringing about these safety benefits. The first step identified is for the State to commission a study that analyzes the utility of intermodal facilities and services available within Tennessee. Specific measures to foster intermodal activity would become apparent from this study. Some of the measures envisaged include encouraging development of additional intermodal terminal facilities in Tennessee, improving access roads to existing terminals, and financing research to develop new technology and also to introduce new technology into the intermodal industry.