The South Dakota Department of Transportation sponsored a study to evaluate the effect of agricultural equipment on flexible pavements. One thin and one thick flexible pavement were instrumented at two locations and tested under agricultural equipment. Each section was instrumented with pressure cells in the base and subgrade, surface deflection gauges, and strain gauges at the bottom of the asphalt layer. Field tests were carried out during fall 2000, spring 2001, and summer 2001 to evaluate the impact of heavy equipment on flexible pavements under variable environmental conditions. Test vehicles included two types of Terra-Gators, a grain cart, and a tracked tractor. The field-testing program collected the pavement responses under five replicates of each combination of test vehicle and load level and under the 18,000-lb single-axle truck. Data were examined for repeatability; the average of the most repeatable set of measurements was calculated and used in the analysis. The first part of the research evaluated the relative impact of the equipment defined as the ratio of pavement response under each combination of vehicle-load level over the pavement response under the 18,000-lb single-axle truck. The analysis of the pavement response ratios indicated that (a) the tracked tractor is not more damaging than the 18,000-lb single-axle truck, (b) Terra-Gators 8103 and 8144 are more damaging than the 18,000-lb single-axle truck only when fully loaded, and (c) the grain cart is more damaging than the 18,000-lb single-axle truck only when loaded over the legal load limit. Data from the second part of the research showed that transporting the commodities using tridem-axle trucks caused far less pavement damage than transporting commodities on agricultural equipment.