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Stuck in the Slow Lane: Undoing Traffic Composition Biases in the Measurement of Trucking Productivity

It is easy to confuse true productivity advances in transportation industries with changes in tonmiles per unit of input that are the result of changes in the composition of traffic, as initially happened with the mid-20th century U.S. railroads. Transportation productivity varies enormously by traffic type, for example, with long-haul versus short-haul traffic. Measurements of changes in physical productivity can easily be biased by modest changes in the traffic mix. We control for endogenous changes in the composition of truck traffic and find that trucking has in fact lagged the U.S. economy as a whole in productivity growth over the period of our data, 1982–1997. Loosening of weight, length, and speed limits is the likely explanation for the growth we do observe. Improvements in information technology have brought real improvements in the quality of trucking services (in reliability, predictability, speed, order tracking, etc.), but as in other service industries, true physical productivity improvements in trucking are limited.