Long-Term Effectiveness of Dynamic Speed Monitoring Displays (DSMD) for Speed Management at Speed Limit Transitions

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Speeding continues to be a significant safety issue on today’s roadways. Studies have demonstrated that increased compliance with properly established speed limits reduces crash incidence and severity. One of the outcomes of Intelligent Transportation System (ITS) technology is the development of practical tools to enable the traffic engineer to more effectively manage speed on their roadway system. The Dynamic Speed Monitoring Display (DSMD) sign is one such tool. These signs measure the speed of the approaching vehicles and then feed this information back to the driver in real time via a dynamic message display. Portable DSMD signs (a.k.a. speed trailers) have been shown to be an effective engineering countermeasure for short-term speed control. However, experience has shown that as soon as the device is removed, speeds soon return to their previous levels.

This paper reports the results of a long-term evaluation of DSMD signs at speed reduction transition zones, which are those locations where the speed limit changes from a higher speed to a lower speed. The study was specifically targeted at locations were a rural highway transitions into an urbanized area. The study found a statistically significant decrease in overall vehicle speed immediately after the installation of the DSMD signs. The average speed reduction across all of the study sites was seven mph and it was found that these speed reductions were maintained over the course of the one year duration of the study. DSMD signs were shown to be effective long-term for speed management at speed transitions zones.