Design and Implement of a Variable Speed Limit System with Travel Time Display – A Case Study in MD, USA

摘要

Variable speed limit (VSL) control system can improve the safety more effectively thantraditional Posted Speed Limit (PSL) control. This topic has received a significant amount ofattention from researchers worldwide. However, little experience is available aboutimplementing a real responsive VSL system backed with advanced control algorithms that cantake account of real-time traffic conditions. This paper presents the structure and algorithm ofthe VSL implemented on MD100 in Maryland, USA. The purpose of this system is to smooththe transition area between uncongested and heavily-congested segments more effectively soas to reduce the potential risk caused by sudden slowdown, and improve the stop-and-goconditions. This system collects the data from traffic detectors and License Plate Recognition(LPR) systems in its real-time operation. The overall condition of the control segment andsegment-by-segment conditions are estimated with travel time data and road-side detectordata. The speed limits at two VSL stations are determined by the combination of pre-plannedscenarios and real-time adjustment. This paper also provides detailed analysis of drivers’responses to the displayed speed limits.