Multi-objective analysis of using U-turns as alternatives to direct left turns at two-way stop-controlled intersections

摘要

This study aims to propose a method to conduct multi-objective analysis of traffic treatments by taking into consideration multiple external impacts. To illustrate the procedure, the economic benefit of converting a two-way stop-controlled (TWSC) intersection to a right turn followed by U-turn (RTUT) intersection was calculated, considering not only the safety impacts but also the operational and environmental impacts. First, vissim simulation models were developed to obtain the total travel time, vehicle emissions, and fuel consumption for the intersection both before and after the treatment. The operational impact was calculated as the travel time saving benefits. The environmental impact was calculated as the reduction in vehicle emissions and fuel consumption costs. The safety impact was estimated as the crash reduction benefits for the RTUT treatment using safety performance functions and crash modification factors (CMFs). CMFs were estimated using meta-analysis methods. Finally, the life-cycle cost method was used to combine different components in the total benefit. The Monte Carlo simulation method was used to conduct uncertainty analysis by using random sampling from probability descriptions of uncertain input variables to generate a probabilistic description of results. The findings showed that, first, the benefits with the use of RTUT treatment can be countervailing even for a single objective. Second, the net present value associated with the RTUT treatment increased with an increase in the proportion of left-turn traffic from the major street when the percentage of left-turn traffic from the major street was from 0% to 22% and became stable after that. The study illustrates the detailed process of evaluating projects considering multiple objectives. This process offers policy and decision makers a solid and practical reference using existing guidebooks and software. The findings also provide suggestions about the suitable condition to install RTUT treatments at TWSC intersections. Copyright (c) 2015 John Wiley & Sons, Ltd.