A modified Chevron N-Layer computer program has the capability of calculating the "work" done by the total load on a given load group. Earlier analyses of AASHO Road Test sections and test vehicles had permitted the development of damage factor relationships. This paper presents seven, namely two-tire and four-tire single axles, tandems, triaxles, and four-axle, five-axle, and six-axle groups. The two-tire axle (front or steering axle) has the most severe damage relationship. The 80-kN (18-kip) four-tire single axle was used as the reference axle and was assigned a damage factor of 1.0 for a specific amount of "work". Other axle arrangements and total loads producing that amount of "Work" were 63.6 kN (14.3 kips) for the two-tire axle, 166.4 kN (37.4 kips) for eight-tire tandems, 250.2 kN (56.25 kips) for twelve-tired triaxles, 333.6 kN (75.0 kips) for a sixteen-tired four-axle group, 415.0 kN (93.3 kips) for a twenty-tired five-axle group, and 496.4 kN (111.6 kips) for a twenty-four-tired six-axle group.

Using the damage factors for the various axle groupings, one trip of a vehicle having a gross weight of 534 kN (120 kips) can produce up to approximately 17 times the damage of an 80-kN (18-kip) axleload, depending on the particular axle groupings involved. Equally as significant effects can be attributed to the distribution of loads on a given type of vehicle. For example, a 355.9-kN (80-kip) vehicle having 53.4 kN (12 kips) on the steering axle and 151.3 kN (34 kips) on each of two sets of tandem axles has an equivalent damage factor of 1.80 per trip. If the load distribution is changed to 40.0 kN (9 kips) on the steering axle and 157.9 kN (35.5 kips) on each of two sets of tandem axles, the total damage factor per trip is reduced to 1.76. Other configurations and various ranges of loads are presented, evaluated in terms of damage per trip, and discussed.

Report Date


Report Number

No. 518

Digital Object Identifier



Accepted for publication by the Transportation Research Board.