Auxiliary exits for freeway incident management - a feasibility study

One of the major problems faced by the traffic engineers and planners in urban areas across United States is the highway congestion caused by incidents resulting in huge delays to the travelers. One of the major components of the ambitious Intelligent transportation system is the Dynamic traffic assignment system, whose purpose is to detect the operational problems on the freeway, estimate the origin-destination pattern of the traffic in vicinity, identify optimal alternative routes for diversion of traffic, disseminate information to travelers, and manage the traffic accordingly. The benefits achieved from the diversion of traffic from freeways to surface streets is constrained by the inadequate lateral capacity, which is the capacity of ramps and weaving sections on freeway, to handle the diverted traffic. This thesis considers the possibility of improving this lateral capacity through use of auxiliary exits which are low-speed, low-cost exit ramps located between the existing ramps on the freeway, specifically used for diverting the traffic delayed by incidents.

The feasibility of these auxiliary exits is tested for differing incident conditions, and diversion scenarios for a prototype traffic corridor developed for the study. The traffic conditions are simulated using a microscopic computer model CORSIM. The diversion scenarios are compared for their relative travel time benefits to the users. The capabilities and problems related to the use of CORSIM model for this study are identified and discussed.

The use of auxiliary exits is an innovative and untested concept for dealing with the diversion of traffic from freeways to surface streets. The results indicate that, after excluding the expensive dual-lane ramps alternative for diversion, the combination diversion strategy using auxiliary exits with existing off-ramps yields significant travel time benefits at the corridor level. The travel time benefits could vary depending on the incident location, duration, and traffic volumes in the corridor. There is a need to study the benefits obtained using the auxiliary exits in more detail considering the factors such as incident severity, different traffic volumes in the corridor, and multiple diversion routes.