A Driving Simulator Study to Analyze the Effects of Portable Changeable Message Signs on Mean Speeds of Drivers

In the United States, between 2003 and 2012, excessive speed was a contributing factor in about one third of all fatal crashes. Intelligent transportation systems (ITS) with the potential to reduce speed and thereby improve safety are therefore of considerable interest. In this article, the mean speeds of drivers affected as a result of four different messages displayed on portable changeable message signs (PCMS) evaluated in an advance-warning area of a work zone are presented. A systematic examination of the combined effects of four sequentially placed PCMS was conducted using a driving simulator (DS). The four messages investigated include speed, state of traffic downstream, and the travel times to exit the work zone. The message sign Prepare to Stop/Stopped Traffic Ahead showed the largest reduction in speed relative to the other messages at a location just upstream of the lane closure. The message also showed the largest overall reduction (30.3 mph, 44.1%) in mean speed compared to a control scenario. Greatest impact on drivers\u27 mean speeds was therefore observed resultant of a strong and clearly worded message. A post-DS experiment survey indicated drivers\u27 ranked the message Speed Ahead 30 mph/X Min To End of WZ as most effective. The drivers complied closely with this message as the mean and 85th percentile speeds were 26.5 and 30.7 mph, respectively, at a location just upstream of the lane closure. This message also showed the second largest overall reduction (26.3 mph, 38.2%) in mean speed compared to a control scenario. The overall reduction in mean speeds was resultant of combined effects of four PCMS in a work zone