The AASHO Road Test, whose original name in English is AASHO Road Test, was an experiment conducted by the American Association of State Highway and Transportation Officials to determine how traffic contributes to the deterioration of highway pavements. This study, carried out since the 1950s in Ottawa (Illinois) "Ottawa (Illinois)")[2] is often the first source of information on experimental data relating to the damage caused by vehicles on roads, for the purpose of road design, and evaluating the cost and profitability of a road.

The experiment was carried out considering a six-lane road, with 3 in different directions on Interstate 80. Each lane was subjected to a specific type of vehicle load and weight. The variation of the pavement structure and its traffic interaction was studied for each lane. "Satellite experiments" were planned elsewhere in the United States to see how climate or slope slope would affect the results, but they were not carried out.

The results of the experiments were used to develop the pavement design guide, the first edition of which came out in 1961 as AASHTO Interim Guide for the Design of Rigid and Flexible Pavements, with better reissues in 1972 and 1993. The 1993 version is still current in the United States. A new guide, originally intended to be released in 2002, was to be the first design guide that would not be based on AASHTO Road Test results.

The AASHTO highway experiments introduced some novel concepts in pavement engineering, including the equivalent load factor. As expected, heavier vehicles reduce the useful life of pavements much more than light vehicles, complying with the so-called Generalized Law of the Fourth Power,[3]​ which explains that the damage caused by vehicle axles is "proportional to the fourth power of the relationship between the weight of the axle and the weight of a standard axle", thus, if one type of axle doubles its weight, the relative damage on the pavement is magnified by a factor of 16.

The other results of the experiment were used to create the "quality assurance regulations" for road construction in the United States, which are still in force today.