UNDERSTANDING THE IMPACT OF INCIDENTS AND INCIDENT MANAGEMENT PROGRAMS ON FREEWAY MOBILITY AND SAFETY

Abstract

Despite significant technological achievements over past decades, and institutional support for Intelligent Transportation System (ITS), it is not possible to prevent all traffic incidents. Numerous incidents occur every day along U.S. freeways and traffic incident management (TIM) programs have been proposed and implemented to mitigate their impact. This dissertation proposes various tools to aid in the evaluation of proposed TIM programs, contributing, thus, to the general study area of freeway incident management. In addition, moving violations specific to concurrent flow lane operations are conceived as a type of transient incident. Their impact on mobility and safety is considered. Techniques to address four key areas are proposed. First, a methodology that considers the dynamics of incident impact given a primary incident's properties and prevailing traffic conditions for identifying secondary incidents from a database is proposed. This method is computationally efficient and overcomes deficiencies of other existing techniques, with utility in any context in which the study of secondary incidents is warranted. A three-stage time-saving process is developed for conducting TIM program benefit evaluations. The process aids in sampling a relatively small set of good quality incident scenarios that can represent historical incident data and overcomes the computational burden encountered when evaluating TIM program's benefit by simulation. Modeling techniques are proposed for simulating violations associated with the operation of concurrent flow lanes. Results from a case study show significant impact to mobility that grows nonlinearly with increasing violation rate. Such illegal traffic maneuvers contribute to increased speed variation and congestion, ultimately affecting safety. Finally, diversion strategies that exploit existing capacity of managed lanes for the purpose of reducing the impact of an incident in the general purpose lanes are evaluated. Simulation modeling methodologies were developed for modeling freeway incidents and studied diversion strategy implementations. Experimental findings indicate benefits of diversion that are contrary to qualitatively developed recommendations in the literature.