Effect of Oregon’s Axle-Weight-Distance Tax Incentive

Oregon’s weight-mile tax was amended in 1990 to provide for a lower tax rate for trucks weighing more than 36 320 kg (80,000 lb) to which axles were added. The additional axles within a weight class reduce the amount of road damage. The tax break was largely based on equity considerations, since trucks within a weight class tend to do less road damage if they have more axles. However, the tax reductions also created an economic incentive to add axles and thus reduce road damage. Whether the tax break actually led to an increase in the number of axles within weight classes and a reduction in the amount of road damage is investigated. Statistical data indicate that a small increase occurred in the number of axles in most weight classes and a large increase occurred in mileage by the heaviest trucks with the most axles. These increases reduced the damage per ton shipped on trucks subject to the axle incentive, but to determine if this was due to the weight-mile tax is not possible. A series of structured interviews supplemented the statistical analysis and indicates that the tax incentive is not a major determinant of truck configuration. One reason for this is that regulatory constraints, particularly weight limits, limit the effectiveness of the tax incentives.