Evaluating the Effects of Queue Warning Systems on Freeway Work Zones Using Traffic Simulation Software

Work zones are a key component of the rehabilitation efforts that travelers on the U.S. national highway system interact with increasingly every day. Roadway construction, rehabilitation, and maintenance poses a potential risk for the travelling public, whether the work is being done within in the vicinity or on the road itself. To minimize risks and increase safety for both drivers and workers, intelligent transportation systems are now being used to remedy deficiencies of current practices. Rear-end crashes are the most predominant type of collision in work zone environments, mainly due to high-speed vehicles approaching a queue of stopped or slow traffic as a consequence of reduced capacity. The sudden reduction of speed in a freeway environment is not usually expected by the motoring public; therefore, innovative approaches have been applied to warn drivers more effectively. A queue warning system (QWS) is a work zone intelligent transportation system comprised of a set of roadside speed sensors and portable changeable message signs (PCMS). The system possesses a customizable speed threshold to detect queued traffic. This information is then relayed to portable changeable message signs that transmit warning mess ages to drivers upstream of the work zone. Currently in Alabama, applications of this technology are still in early stages. For the purposes of this research, traffic simulation software is used to investigate the effects of QWS on freeway traffic. A freeway work zone environment with a lane closure is modeled using field-gathered speed data, volumes, and vehicle length. This study proposes a set of six different speed reduction schemes in advance of the lane closure that simulate the QWS effect on three sets of non-compliant driver proportions. Statistically significant differences are found between some of the proposed speed reduction schemes and between non-compliant driver proportions. From the analysis of results, conclusions are drawn and recommendations for practitioners are made based on speed differential measures for future safety enhancement using QWS application and deployment on freeway work zones.