Risk-and-Reliability-Based Approaches to Analyzing Road Geometric Design Criteria

US Transportation Collection2019PDFTech ReportPorter, Richard J.Musunuru, AnushaShea, Michael ScottUniversity of Utah. Department of Civil and Environmental EngineeringMountain Plains ConsortiumNorth Dakota State UniversityUnited States. Department of Transportation. University Transportation Centers (UTC) ProgramMountain Plains ConsortiumUnited StatesAuxiliary lanesCrash ratesCrash severityGeometric designHighway designHighway safetyRamps (Interchanges)Regression analysisReliabilityRisk analysisMPC-19-408Federal and state transportation agencies set goals related to surface transportation system performance. The variability in factors influencing design criteria (e.g., driver performance, road conditions, and vehicle performance) is often large and is addressed implicitly by using \u201cconservative\u201d values. However, a risk-and-reliability-based analysis in roadway geometric design is proposed in this research to address these gaps. Probabilistic geometric design analysis is well suited to explicitly address the level of variability and randomness associated with design inputs when compared with a more deterministic design approach. This research critically assesses alternative approaches for incorporating risk and reliability analysis when establishing road geometric design criteria and design decisions. An in-depth investigation of the applicability of reliability analysis was done and a reliability analysis was used to estimate the probability distribution of operational performance that might result from a basic number of lanes decisions made to achieve a design level of service on a freeway. Geometric effects of freeway ramp spacing and auxiliary lane presence on crash frequency and crash severity were also analyzed. Negative binomial and multinomial logit regression models are used to estimate the effects of ramp spacing and auxiliary lane presence on expected crash frequencies and crash severities, respectively.120