Evaluation of a warning system to reduce the risk of casualty crashes at rural junctions in South Australia

Abstract

Objective

This study evaluated the effectiveness and potential safety benefits of a Rural Junction Active Warning System (RJAWS), which uses variable speed limit signs (VSLSs) to temporarily impose a reduced speed limit along the major road when another vehicle is approaching on the minor road or turning into the minor road from the far-side major leg.

Methods

The RJAWS was trialed at 4 3-leg rural junctions between 2-lane roads in South Australia. A quasi-experimental before–after analysis was conducted. The free-flow speed of vehicles along the junction major approaches was used as an indicator of the risk of a casualty crash with adjacent traffic. Events with activated and nonactivated VSLSs after the RJAWS installation were analyzed separately. Travel speed, speed limit compliance, and the relative risk of a casualty crash were compared. The potential risk of casualty crashes relative to traveling at the default speed limit was calculated based on a known relationship between travel speed and relative casualty risk for rural roads in South Australia.

Results

When the reduced speed limit signs are activated, the average travel speed along the major road is reduced between 11.3 and 22.1 km/h, with a consequent reduction of the expected average casualty risk between 42% and 65% compared to before the RJAWS installation. . Though compliance with the reduced posted speed limit was low, the RJAWS still proved effective in reducing travel speed because the majority of drivers traveled through the monitored junctions at speeds below the default speed limit when the sign was activated.

Conclusions

This evaluation indicated that the trialed RJAWS can potentially reduce the risk of fatal and serious injuries at junctions under conditions that may present the opportunity for an adjacent-direction collision with another vehicle. Extending the RJAWS installation to additional junctions is strongly suggested. Further monitoring is needed to determine whether safety benefits are sustained over the long term.

Keywords:

• Rural junctions
• automated warning systems
• intelligent transport systems
• RJAWS
• speed limits
• road safety

Acknowledgments

We thank the following individuals at the South Australian Department for Infrastructure and Transport for providing RJAWS trial data and relevant information: Kerry McConnell, Amit Dua, and Neil Loveridge. Thanks also go to the anonymous reviewers for their valuable comments, which helped improve the quality of the article.

Additional information

Funding

This work was supported by the South Australian Department for Infrastructure and Transport under Grant number 1701195780