EFFECT OF ROAD SURFACE ON VEHICLE SPEED

124 observations relating to sites where both speed and surface standard were registered have been analysed. Surface standard was measured by IRI (International Roughness Index) and speed as space mean speed. Multiple regression was used. It is found that speed of cars is reduced when rut depth and irregularity (IRI) increase. There is no appreciable change in speed of lorries and lorry-trailer combinations when road surface standard changes. For the covering abstract of the conference see IRRD 875360.