The correlation between speed and road surface condition is of interest for the planning of pavement maintenance on the road network. The costs and the target variables that are affected by this correlation are, in addition to travel time, fuel consumption (vehicle costs), energy and environment. According to previous studies of the road surface influence on the vehicle speed increased rut depth (RUT) and increasing longitudinal road unevenness (IRI) causes decreased vehicle speed. In the description of the road surface macro texture (MPD) is normally also included. There has, however, been a lack of knowledge about the importance of MPD on vehicle speed.
The main purpose of the present study was to supplement existing knowledge about the vehicle speed with the importance of MPD.
This study of velocity as a function of road surface has been based on existing data from spot speed (TMS) and road surface measurements (RST). Both of these data sets are developed within the Transport Administration’s annual comprehensive measurement program.
The types of vehicles included in the study are: light vehicles without trailers (pbu); light vehicles with trailers (pbs); heavy three-axle vehicles without trailers (lbu) and heavy vehicles with trailers (lbs).
The road properties included in the study as explanatory variables are: road width; speed limit; horizontal curvature (ADC); vertical curvature (RF); routing (track); roughness (IRI) and the macro texture (MPD).
Road width and the speed limit are included for classification. Large differences in road surface effects on speed have been established between 70- and 90-road, which is supported by a literature reference. This indicates that this condition shall be considered. Both of pbu and lbs and for the two types of road, the road surface is more significant for the resulting speed than the road geometry of the TMS-spots median conditions. Within the group of road surface variables IRI is the most important variable, then MPD and finally RUT.
The need for further research in this area is assessed as very high.