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Classic highway traffic flow theory can explain the evolution of signals and waves once they form. Given sufficient boundary conditions the theory captures the evolution of the traffic state over space and time. But one rarely finds such ideal boundaries on real highways. Often disturbances arise within a region that classic theory would tell us should be homogeneous. These disturbances often grow and give rise to unstable traffic upstream, e.g., resulting in stop-and-go conditions during congestion with an increased frequency of accidents. This talk will examine one potential source of these disturbances, namely the fact that after a lane change maneuver drivers accommodate an entering vehicle quicker than a departing vehicle (mandatory accommodation versus discretionary accommodation). After illustrating this imbalance on two facilities, the talk will explain how it can give rise to lasting disturbances.

Dr. Coifman is an associate professor at the Ohio State University with a joint appointment in the department of Civil and Environmental Engineering and Geodetic Science and the Department of Electrical Engineering. His research emphasizes extracting more information about traffic flow both from conventional vehicle detectors and emerging sensor technologies. His work has been recognized by the ITS America Award for The Best ITS Research and an NSF CAREER award. Dr. Coifman...

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In this seminar, Dr. Porter will explore the interactions of geometric design decisions, speed, and safety. A performance-based approach to this topic will be considered given the availability of several key documents, including the Highway Safety Manual and TRB's Modeling Operating Speed: Synthesis Report as well as a significant body of published research. A historical look at the design speed concept will show that while the design speed definition has changed on more than one occasion, the same basic but flawed philosophy that relates design speed to a “safe speed” is still reflected in supplemental guidance related to design speed selection in current design policy. A conservative approach to establishing design criteria, currently used to address the range of driver, vehicle, and roadway conditions and capabilities that a designer must consider, will be demonstrated. Resulting operating speeds will be shown to be higher than design speeds for design speeds of approximately 55 mph or less. This outcome may be considered undesirable...

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