Can Changed Speed Limit on a Road Section Influence Speed on Adjacent Sections

The purpose of this paper is to analyze whether or not changed speed limits on a certain section of road can influence speed in other sections as well as to discuss alternate behavioral possibilities. This paper presents a case study on two road sections in Norway. Speed limits were changed from 90 to 80 or from 90 to 100 km/h, and speed measurements were made both on the road sections where the limits were changed and on adjacent sections. Previous research indicates that changing the speed limit on a road section may affect driving speeds even on road sections where the limit remains unchanged. In order to assess to what extent speed changes on the adjacent road section can be attributed to the speed limit change, speeds of vehicles coming from the section with changed speed limit were compared to that of vehicles in the opposite direction. On both roads the speed on adjacent sections changed in the same direction as the speed limit change. Although the effects were rather small (1 – 2 km/h), they may have significant implications for crash risk.