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Title:Risk-and-Reliability-Based Approaches to Analyzing Road Geometric Design Criteria
Authors:Richard Porter, Anusha Musunuru, and Michael Scott Shea
University:University of Utah
Publication Date:Oct 2019
Report #:MPC-19-408
Project #:MPC-406
TRID #:01767617
Keywords:auxiliary lanes, crash rates, crash severity, geometric design, highway design, highway safety, ramps (interchanges), regression analysis, reliability, risk analysis
Type:Research Report – MPC Publications


Federal 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 "conservative" 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.

How to Cite

Porter, Richard, Anusha Musunuru, and Michael Scott Shea. Risk-and-Reliability-Based Approaches to Analyzing Road Geometric Design Criteria, MPC-19-408. North Dakota State University - Upper Great Plains Transportation Institute, Fargo: Mountain-Plains Consortium, 2019.

NDSU Dept 2880P.O. Box 6050Fargo, ND 58108-6050