Preliminary evaluation of Rural Junction Activated Warning System (RJAWS) in rural South Australia

Abstract

This report describes a preliminary evaluation of the potential for the Rural Junction Activated Warning System (RJAWS) to reduce the travel speed of approaching vehicles on the major legs of a three-leg junction when another vehicle is detected on the minor road or turning right from the far-side major leg into the minor leg. When the RJAWS detects any of those two conditions, an electronic sign placed on each approach direction along the major road temporarily indicate a speed limit lower than the default limit. The system has been installed at four rural junctions in South Australia characterised by poor sight distances. At three of the four trial locations, the default and reduced speed limits are 80 km/h and 50 km/h, respectively; whereas at one of the trial locations a default speed of 100 km/h and a reduced speed of 70 km/h applies. Pre and post RJAWS installation speed profiles of vehicles travelling along the major road have been compared. When the temporary speed limit signs are activated, the average travel speed along the major road is reduced by 11.3 km/h to 22.1 km/h. Consequently, the expected average relative risk of a casualty crash at the trialled junctions is reduced by 42% to 65% compared to before the RJAWS installation. Despite a limited compliance with the reduced speed limit, the proportion of drivers travelling through the junction at speeds 20 km/h or higher than the reduced speed limit was considerably low when RJAWS is activated, indicating the system effectiveness in reducing risky behaviour when another vehicle is at the junction. An extension of the RJAWS program to additional junctions is strongly suggested. Also, further investigation should be carried out to confirm the findings of this study through a control-case before/after analysis with a larger and more accurate speed data sample.