Abstract
The aim of the project was to investigate the relation between road surface roughness recorded as IRI (International Roughness Index, mm/m) and the resulting speed reduction, if any. The influence of rut depth on speed has also been studied. Speed data from the VTI and data on road surface condition recorded by Road Survey Technology (RST) have been used in multiple linear regression analysis. The results indicate a speed reduction for passenger cars when IRI and rut depth increase. Trucks with and without trailers respectively show no speed reduction with increased road surface roughness or rut depth. (A)