Evaluation of the Effectiveness of a Variable Advisory Speed System on Queue Mitigation in Work Zones

• Main Author: Wilson, Aaron B.
• Format: Others
• Published: BYU ScholarsArchive 2011
• Subjects: variable; speed; advised; VASS; VMS; VSL; Civil and Environmental Engineering
• Online Access: https://scholarsarchive.byu.edu/etd/2504; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=3503&context=etd

Construction is increasing due to increased demand and degradation of existing infrastructure. This construction often results in a reduced number of traffic lanes or lane width during construction, which often creates queue at the entrance to work zones. Variable Advisory Speed Systems (VASS) provide drivers with advanced warning regarding traffic speeds downstream to help them make better decisions in advance of problems that may exist downstream. The purpose of this study was to evaluate the effectiveness of a VASS at mitigating queues in work zone entrances during peak hour conditions. It was anticipated that by implementing a VASS queues would be reduced and vehicle flow increased in work zone areas. Three objectives of this study were: (1) research VASS systems that are available to be tested, (2) select and deploy a VASS in Utah at a long-term work zone, and (3) perform a statistical analysis on traffic flow characteristic data to evaluate the effectiveness of the VASS on queue mitigation. A literature review on the use of VASS for work zones returned minimal studies on advisory speeds in work zones. Most of the advanced speed notification systems, found during the literature review, used variable speed limit (VSL) applications. A VASS was selected and deployed at the northbound approach to the I-15 Beck St. widening project in North Salt Lake City. In this study the VASS consisted of five sensors and two variable message signs (VMSs). To determine if the system was effective at reducing queue the speed data were analyzed in detail to come to statistical conclusions. The collected data shows that the VASS investigated was effective on weekends during evening peak hours when there was a slow down. No consistent significance was seen on week days during the evening peak. There was no statistical difference between before and after speed data on any day of the week when there was no slow down. This study is valuable because it is unique in studying an advisory speed using VMSs and other ITS technology. This study recommends that further studies be conducted without a movable median barrier system, as was used in this construction project, to evaluate further about the effectiveness of VASSs. It is recommended that, if a VASS is considered, studies be done to see whether queues are expected to form at the work zone entrance, as VASSs will not be effective if queues do not form.