Advancing performance-based highway geometric design

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The conventional approach to highway geometric design relies on adherence to criteria based mainly on empirical data that relate driver/vehicle performance to geometric characteristics (nominal safety). Acceptable performance is presumed to be produced through proper application of the technical guidance, but is nonetheless an indirect outcome of the process, which produces physical design dimensions. Recently, designers have begun to recognize that design should be based on actual performance, including crash experience (substantive safety), mobility, and cost. Performance-based (PB) geometric design has been sporadically applied using such concepts as reliability analysis, value engineering, and context-based design. It has also been aided by several recent developments, most notably Interactive Highway Safety Design Model, Highway Safety Manual, and Roadside Safety Analysis Program. These developments provide designers with better analysis tools than the conventional approach. However, they generally focus on single performance measures because of two knowledge gaps: (1) some performance measures are not well understood and have not been yet quantified and (2) a comprehensive methodology that simultaneously considers all relevant performance measures is lacking. Recognition of the fundamental interactions among performance measures implies the need for more formal and comprehensive tools to aid broader implementation in practice. This need has been recognized by researchers and practitioners. The proposed research addresses this need for two types of highway facilities: roundabouts that are emerging as viable intersection type and rural two-lane highways that share a substantial proportion of crashes in the highway network. For each highway facility, the objective of the proposed research is first to model relevant performance measures and then to integrate them in a multi-objective decision-support system. This research will initiate unprecedented efforts in building strong, comprehensive decision-support systems that directly incorporate relevant performance measures within the design process itself, rather than in an external manner, as is the case today. As such, these systems would guarantee cost-effective solutions and would inevitably produce roadway designs that differ from one location to another, reflecting differences in local context, project objectives, and relative values. The research will promote continued development of PB design for other highway facilities (eg, rural multi-lane highways and signalized intersections) and for other road users (eg, bicyclist and pedestrians). The developed decision-support systems will enable practitioners to compare key design trade-offs and make better informed decisions. The proposed research is timely and innovative, and  will aid the reputation of Canadian highway design research.