VISSIM Microsimulation Research Articles

VisSim-Based Genetic Algorithm Optimization of Signal Timings

Genetic algorithm optimizations of traffic signal timings have been shown to be effective, continually outperforming traditional optimization tools such as Synchro and TRANSYT-7F. However, their application has been limited to scholarly research and evaluations. Only one tool has matured to a commercial deployment: direct CorSim optimization, a feature of TRANSYT-7F. A genetic algorithm formulation, VisSim-based genetic algorithm optimization of signal timings (VISGAOST), is presented; it builds on the best of the recorded methods by extending their capabilities. It optimizes four basic signal timing parameters with VisSim microsimulation as an evaluation environment. The program brings new optimization features not available in the direct CorSim optimization, such as the optimization of phasing sequences, multiple coordinated systems and uncoordinated intersections, fully actuated isolated intersections, and multiple time periods. The formulation has two features that enhance and reduce computational time: optimization resumption and parallel computing. The program has been tested on two VisSim networks: a hypothetical grid network and a real-world arterial of actuated–coordinated intersections in Park City, Utah. The results show that timing plans optimized by the genetic algorithm outperformed the best Synchro plans in both cases, reducing delay and stops by at least 5%.

Upstream Signalized Crossover Intersection

Left turns have a significant impact on the operation and performance of signalized intersections. Therefore, researchers have investigated alternative measures to improve the performance of intersections with heavy left-turn movements, some of which have been unconventional schemes. One of these schemes is the upstream signalized crossover (USC), a four-legged intersection designed to eliminate left-turn-opposing conflicts by crossing the left and through traffic to the left side of the road at all four approaches prior to the intersection. Crisscrossing action is achieved through the use of a secondary two-phase signal at each crossover point. This research investigated signal optimization strategies for USC intersections and identified important operation issues. The VISSIM microsimulation program was used to model and analyze the unconventional USC intersection and, for comparison, a conventional intersection. The analysis revealed that, for relatively balanced volumes, a USC intersection can significantly reduce average vehicle delays, particularly when the volumes entering the intersection are relatively high. More important, the capacity of the USC intersection was found to be approximately 50% greater than that of a conventional intersection with similar geometry under balanced traffic volumes. For highly unbalanced volumes, particularly when the intersection volumes were relatively low, a conventional intersection outperformed the USC intersection. Overall, the USC intersection showed considerable potential for situations in which one or more of the following conditions exist: (a) intersection volumes are balanced and near or over the capacity of a conventional intersection, (b) traffic volumes are somewhat unbalanced, but the overall entering volumes are too high to be accommodated with a conventional intersection, or (c) the intersection has heavy left-turn volumes that cause excessive delays.

Upstream Signalized Crossover Intersection: Optimization and Performance Issues

Left turns have a significant impact on the operation and performance of signalized intersections. Therefore, researchers have investigated alternative measures to improve the performance of intersections with heavy left-turn movements, some of which have been unconventional schemes. One of these schemes is the upstream signalized crossover (USC), a four-legged intersection designed to eliminate left-turn-opposing conflicts by crossing the left and through traffic to the left side of the road at all four approaches prior to the intersection. Crisscrossing action is achieved through the use of a secondary two-phase signal at each crossover point. This research investigated signal optimization strategies for USC intersections and identified important operation issues. The VISSIM microsimulation program was used to model and analyze the unconventional USC intersection and, for comparison, a conventional intersection. The analysis revealed that, for relatively balanced volumes, a USC intersection can signific...

Determination of Optimal Detector Location for Transit Signal Priority with Queue Jumper Lanes

Transit signal priority (TSP) is an operational strategy that facilitates movement of transit vehicles through signalized intersections. As an important component of a TSP system, the transit vehicle detection system plays a key role in determining when to trigger TSP and which TSP strategy to use. This paper presents an analytical method to determine optimal detector locations for intersections implemented with TSP and queue jumper lanes. A queue jumper lane is a preferential treatment for buses that designates a short stretch of a special lane, such as a right-turn bay, to allow buses to bypass a traffic queue and then to proceed ahead of the queue by means of an early green signal for that lane. In this study, a comprehensive TSP strategy was used that considers early green, green extension, special phase insertion, coordination recovery, green reimbursement, and maximum number of continuous TSP requests. An analytical method for determining optimal detector locations under this TSP strategy for different bus arrival conditions was proposed. The effectiveness of the proposed method was verified with the VISSIM microsimulation model, and results show that the method is able to identify optimal bus detector locations for TSP with queue jumper lanes.

Induced Travel and Emissions from Traffic Flow Improvement Projects

Two scenarios for improving traffic flow are simulated and analyzed using the VISSIM microsimulation model and the Comprehensive Modal Emissions Model. Short-run and long-run emissions of CO, HC, NOx, and CO2 and fuel consumption are estimated. In the short run, with traffic volumes held constant, results demonstrate that the smoothing of traffic flow will result in reduced emissions. Long-run emissions are simulated by synthetically generating new trips into the simulated networks to represent potential induced travel. This is done until a “break-even” level of emissions for each pollutant and fuel consumption is reached that is equivalent to the base level before the traffic flow improvement was added. By also calculating short-run changes in travel time from the improvement, the travel time elasticity equivalents for each pollutant are calculated. These values are compared with travel time elasticities in the literature to evaluate whether long-run emissions benefits are likely to endure. Simulations are conducted using different assumptions of vehicle soak time to simulate cold-start and hot-stabilized operating modes. Results indicate that, in most cases, long-run emissions reductions are unlikely to be achieved under the two scenarios evaluated.