Vertical accelerations of a passenger in an automobile are automatically summed while traveling a section of road at 51.5 mph (23.0 m/s). A roughness index is obtained by dividing this sum by the time elapsed during the test. Continuity in measurements since 1957 has been preserved through correlations among successive vehicles involved and reference pavements.

In general, bituminous construction has yielded smoother-riding surfaces than concrete construction. The smoothness of concrete pavements, however, has improved on those projects where slip-form paving was used. Interstate and parkway (expressway) construction continues to yield smoother pavements than other major construction. The rate of increase in roughness was found to be different for each pavement type and varied according to the original or as-constructed roughness of the pavement, structural number, and the type of highway facility involved.

Report Date


Report Number

No. 371

Digital Object Identifier



Offered for publication to the Highway Research Board.