A new roughness index called the dynamic load index (DLI) is developed for the purpose of identifying pavement profiles that are likely to generate high dynamic truck-axle loads. The DLI is calculated as a weighted index of variances of the profile elevation in the frequency ranges of 1.5 to 4 Hz and 8 to 15 Hz. The first frequency range corresponds to truck body bounce, and the second frequency range corresponds to axle bounce. The analysis showed a very good relationship between the DLI and dynamic load. The DLI was tested on a range of road profiles from in-service pavements, and it was found that for any particular value of ride quality index (RQI), the DLI can cover a wide range of values, and this variation in DLI was found to correlate well with dynamic load, as predicted by a truck simulation program. This was not the case for the international roughness index, which gave a low coefficient of correlation with dynamic load for the same range of profiles. Therefore, the new index can differentiate between profiles that generate high dynamic loads and those having the same RQI but generating low dynamic loads. Most importantly, the use of the DLI negates the need for running a truck simulation program. This makes it possible for a state highway agency to decide whether a particular pavement with a given surface profile needs smoothing (to extend its service life) based on the DLI value.
Abstract