Congressional Budget Office / by David Austin
Although freight transport contributes significantly to the productivity of the U.S. economy, it also involves sizable costs to society. Those costs include wear and tear on roads and bridges; delays caused by traffic congestion; injuries, fatalities, and property damage from accidents; and harmful effects from exhaust emissions. No one pays those external costs directly—neither freight haulers, nor shippers, nor consumers. The unpriced external costs of transporting freight by truck (per ton-mile) are around eight times higher than by rail; those costs net of existing taxes represent about 20 percent of the cost of truck transport and about 11 percent of the cost of rail transport.
This study examines policy options to address those unpriced external costs. The options would impose taxes based on the weight or distance of each shipment, increase the existing tax on diesel fuel, implement a tax on the transport of shipping containers, or increase the existing tax on truck tires. The analysis estimates what would have occurred in 2007 had the simulated policies already been in place and had any initial, short-term transitions in response to the policies already occurred.
Adding unpriced external costs to the rates charged by each mode of transport—via a weight-distance tax plus an increase in the tax on diesel fuel—would have caused a 3.6 percent shift of ton-miles from truck to rail and a 0.8 percent reduction in the total amount of tonnage transported. Such a policy would have eliminated 3.2 million highway truck trips per year and saved about 670 million gallons of fuel annually (including the increase in fuel used for rail freight). On net, accounting for the effect of fuel savings on revenue from the fuel tax, such a policy would also have generated about $68 billion per year in new tax revenue and reduced external costs by $2.3 billion. Adopting instead the other policy options that were studied would have resulted in smaller changes in tonnage and ton-miles and smaller increases in tax revenue. All of the policy options would have narrowed the gap in the share of external costs paid in taxes by truck versus rail.