Unconventional Intersection Control Strategies for Urban Evacuation

Intersections form one of the biggest challenges to emergency managers when evacuation plans are developed in urban areas. Signalized intersections reduce the directional capacity of a roadway because they must allocate the right-of-way between competing movements and approaches. In response to this problem, a variety of unconventional intersection control strategies have been developed for implementation during evacuations. Three of the most common are manual traffic control (MTC), flashing yellow signals, and crossing elimination. Fundamentally, each of these strategies has demonstrated strengths and weaknesses, but little work has been done to evaluate them systematically in an apples-to-apples comparison. The goal of this study was to determine which unconventional intersection control strategy was best suited for a given urban evacuation scenario. With results generated by the microscopic traffic simulation software VISSIM 7.0, a dynamic program identified the optimum control strategy for various evacuation scenarios. One general finding of this research was that MTC was best suited for intersections immediately upstream of a bottleneck or for closely spaced, uncoordinated signals. Flashing yellow signals appeared to work well for intersections with high, unbalanced demand and low volumes on the minor approach. Crossing elimination strategies worked best when demand from nonconflicting directions was high and all other approach volumes were relatively low. In practice, these control strategies can be used in combination with other evacuation techniques such as zone phasing and contraflow to utilize network capacity better and to decrease clearance time.