The attached report, "Dynamics of Sprung Loads on Pavements," resulted from a need for reliable impact factors for use in the structural design of pavements. For some years, it has been customary to use 1.2 times the static wheel load for designing portland cement concrete pavements. We, along with other investigators, have questioned this value, and have actually used higher values for some specific conditions. Impact factors for specific situations are listed on page 33 of the report. The three roads classed as smooth averaged 1.25, while the rough road gave a value of 1.35. Depressions at culverts and bridge approaches gave average values of 1.58 and 1.49 respectively. It appears that pavement design impact factors of 1.20 are too low and should be in the order of 1.33 to 1.50.

Report Date


Report Number

No. 174

Digital Object Identifier