Abstract Manager

Enforcing speed limits has a substantial impact on both highway mobility and safety. While Increasing the posted speed limit can create the perception of improving highway efficiency, it concurrently heightens the likelihood of accidents.

This study utilized a reliability-based model to evaluate the safety implications associated with elevating speed limits on highways. The research methodology is applied to diverse highway sections, encompassing both horizontal and vertical curved segments. In each segment, the crucial instances of failure to comply were assessed. The study assessed the critical instances of noncompliance for each segment, considering a speed increment of 10 km/hr (100, 110, 120, and 130 km/h) to quantify the heightened risk accompanying the speed limit increase.

The findings show a significant adverse impact of increasing the speed limit. The risk ratios for a 10 km/hr speed limit augmentation increased significantly, particularly concerning insufficient sight distance on curved sections. Regarding the vertical curves, the risk ratio for crest curves exhibited a considerable increase in risk, whereas the risk for sag curves saw an average rise with a lower risk ratio than crest curves. As jurisdictions in North America contemplate increasing freeway speeds from 100 km/hr to 120 km/hr, this study applies the established framework to evaluate the proposed speed limit increase. The results show substantial additional risks, utilizing actual freeway data and characteristics obtained from field observations, despite the conservative road design. The framework proposed in this study advocates for a proactive safety approach, encouraging practitioners to thoroughly assess the potential impacts of speed limit adjustments before implementation.

Prior to raising speed limits, it is advisable to implement measures that enhance sight distance. Countermeasures such as Enhanced Delineation treatment, increased pavement friction, Roadside Design Improvement, relocation of median barriers to maximize middle ordinate distance, and conveying warning messages through Dynamic Message Signs (DMSs) are examples of interventions that can effectively improve sight distance on highways.