AASHO Road Test tandem axleloads were analyzed to determine the magnitude of the tandem axleload that causes the same damage as the 18-kip (80-kN) single axleload. The procedure is outlined and is the same used to analyze single axleloads. The essential findings were as follows:

1. One repetition of a 34-kip ( 151-kN) tandem axleload appears to cause the same damage as one repetition of an 18-kip (80-kN) single axleload. 2. The relationships of log repetitions versus axleload used by Kentucky appear to be equally valid for single and tandem axleloads. 3. The use of superposition principles, and equivalency of repetitions, in combination with terminal serviceability indices permitted analyses of the tandem axleload data and comparison with equivalent Kentucky thickness designs converted to the AASHTO structural number. 4. Single axleload analyses were combined with the tandem axleload analyses and superimposed by Kentucky equivalent designs. The Kentucky designs, based upon elastic theory, enveloped 91 percent of the AASHO Road Test data. 5. For pavement design, the estimated fatigue for a 20-year design using the AASHTO damage factors will be reached in 16.2 years using the Kentucky damage factors. The Kentucky damage factors more closely approximate observed behavior than the AASHTO factors.

Report Date


Report Number

No. 483

Digital Object Identifier



Offered for publication to the Transportation Research Board.