Traffic Microsimulation Approach to Evaluation of Vehicle Emissions on One-Way Versus Two-Way Streets: Case Study in Downtown Houston, Texas

Vehicles that run on one-way or two-way streets may generate totally different emissions. One-way streets can reduce the amount of conflicts between vehicles going to different directions, but sometimes create circuitous routes which may increase Vehicle Miles Traveled (VMT) and travel times, thus may increase emissions. Two-way streets can avoid circuitous routes, but create slower traffic due to the existence of more moving conflicts between vehicles, which may lead to increased stop, acceleration-and-deceleration activities, thus may also increase emissions but at a different degree. Further, regularities of such emission increases may be different for peak vs. non-peak hours. This paper intends to evaluate vehicle emissions for one-way and two-way streets for peak vs. non-peak hours to investigate which street configuration produces relatively lower emissions, attempting to help traffic engineers decide whether a conversion between one-way and two-way streets contributes to the improvement of air quality. The micro-traffic simulation model—VISSIM—is utilized to output the second-by-second speed and acceleration data for the purpose of emission estimation. The operating mode binning approach is used to calculate emission factors, and differences of generated emissions are adopted as the measure of effectiveness. The analysis shows that the two-way street network produces lower emissions, thus can better improve the air quality during non-peak hours. However, such improvement will be weakened during peak hours. Further, emissions from the two-way street network may eventually exceed those from the one-way street network when the traffic demand increases to certain level.