Road safety audits: quantifying and comparing the benefits and costs for freeway projects

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University of New Brunswick


Although formal Road Safety Audits (RSA) have become a common review process for large-scale highway development projects throughout Canada, there is a limited understanding of the net safety benefits that they provide. Government entities, with restricted infrastructure budgets, continue to seek evidence that collision reduction methodologies have a significant, economically efficient influence on the safety of highways within their jurisdictions. This study attempted to identify and quantify the impacts that RSAs have had on the design/development of three large, mainly rural freeway projects, with similar fundamental characteristics (e.g., functional classification, cross-sectional geometry, RSA Team, and project budget). This research involved examining and quantifying RSA findings from different project stages (Design, Pre-Opening, and Post-Opening), as well as comparing observed and predicted collision frequencies, in order to develop a better understanding of the safety impacts that may be attributed to the review process. The results of this study indicate that including RSAs in the development process for large Public-Private-Partnership (P-3) projects has significantly reduced the overall frequency of collisions on these types of facilities. It was found that the New Brunswick projects experienced approximately 15% fewer collisions overall (effectively producing a collision modification factor (CMF) of 0.85 for rural freeways), or a reduction of 0.12 collisions per kilometre per year. When the safety benefits were contrasted with the audit costs for each of the three freeway projects, the estimated Benefit-Cost (B/C) ratios ranged from 50:1 to 65:1, and yielded an average ratio of 55:1. Following a sensitivity analysis of discount rates and collision costs, the most conservative overall average B/C estimate was found to be 20:1. The study findings indicate that the savings attributable to RSAs far outweigh the associated costs, confirming that the RSA process is one of the most cost-efficient investments in road safety that a road authority can make. The overall finding of this study, that RSAs can have a significant, economically efficient impact on the safety performance of highway facilities, provides evidence to support increased employment of audit programs in order to develop the safest road networks possible.