Axle Weight Limits for Single and Tandem Axles

Axle load limits for single axles, 89 kN ($\approx 20\mathrm{kips}$), and tandem axles, 151 kN ($\approx 34\mathrm{kips}$), are set to control potential pavement damage. These axles, at their corresponding weight limits, are considered equivalent. Because pavement layers are more complicated than a linear elastic material, using linear elastic theory would result in erroneous loading response prediction and, hence, potential pavement damage. Thus, actual tandem- and single-axle loading, along with flexible pavement structure, were modeled using an advanced finite-element model. The influences of a 1.2-m-spaced tandem axle and a single axle on flexible pavement responses were assessed qualitatively. Transfer functions from AASHTOWare were used to compute pavement distresses. Tandem and single axles were found to be inequivalent, confirming that the distresses due to the tandem axle were greater than those of the single. Load equivalency was calculated for different parameters, such as tire type, pavement material, and structure. The load equivalency was found to be dependent on various parameters. Wide-base tires (tire type) had the highest influence on the weight limits [135 kN ($\approx 30\mathrm{kips}$)]. Because 72% of national goods are moved on highways, accurate weight limits should be applied using an established equivalency factor.