Road users´ requirements on road surface condition: A driving simulator study

In order to get a view on the road surface condition the Swedish Road Administration (SRA) uses both objective measurement mehods, mainly measurements of rut depth and unevenness, and road users, opinions on the roads condition. Objective measurements show that road surface condition in general has not changed to any greater extent during the latest years. Road user surveys show, however, that the road users, and not least the professional drivers, have become less satisfied with the operation and maintenace of the roads. To try to understand the cause of this discrepancy it is of interest to closer analyse the road users assessment of road surface condition. The report presents a driving simulator study, which is divided into two experiments. In the first experiment the importance of different impressions, i.e. visual appearance, noise and vibrations, is tested on a road surface with ruts as well as on a road surface with patchings/repairs. The analysis was based on driving data and on the drivers´ opinions on how comfortable and safe, respectively, the road was to drive on. The conclusion from the first experiment was that the visual apppearence alone does not influence speed, but lateral position. Noise has an influence on the variance of speed, and vibration has an influence on the variance of lateral position. Noise and vibration have an influence on speed in interaction with the visual appearance. The results of the drivers´ assessments of comfort and safety show a clear pattern where the visual appearance, the sound and the vibrations separately and in an additional way have an influence on the subjective experience of comfort and safety. In the second experiment eight road surfaces with different road surface conditions (patches, ruts, ruts filled with water, rough texture, unnevenness (two levels), cracks and edge deformations). The eight road surfaces grouped together in three different groups concerning the assessment of comfort and of safety, though not in the exact same way.