Transportation agencies have traditionally relied on historical crash records as the primarymeasure to evaluate the safety of roadways. The infrequent and sporadic occurrence of accidents,and the long period of time required to collect accident data have led to the use of surrogatesafety measures. Conflict analysis using microsimulation modeling has been popularized forevaluating experimental changes to existing road networks. Previous freeway studies have used asimplified time to collision (TTC) definition, which in this study was found to produceunrealistic conflict situations. More specifically, the definition included situations where nocollision path was occurring, such as when two vehicles were travelling at the same speed orwhen the leading vehicle was speeding away from the following vehicle. A revised conflictdefinition is developed to address these issues and is then contrasted with the simplifieddefinition used in earlier studies. An investigation of acceleration rates demonstrates that therevised approach retains the meaningful conflicts produced by the previous definition, buteliminates the situations which are unlikely to be actual conflicts. Using this revised conflictdefinition, the evaluation of a truck-only highway in the Greater Toronto Area (GTA) isinvestigated to observe the effects on traffic conflicts. In general, it was found that whileproviding a separate highway for trucks does reduce truck-related conflicts, car lane changeconflicts increase due to their increased maneuverability and presence on the truck-free highway.
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