Midwest States Smart Work Zone Deployment Initiative: MwSWZDI Technology Evaluations Year One - Chapter 5: Nebraska - SpeedGuard Radar Speed Reporting System
This study evaluated the impact of deploying a portable speed warning sign to control traffic speeds in work zones by informing vehicles of their speed in relation to posted speed limits on interstate I-80 in Nebraska. The SpeedGuard Radar Speed Reporting System was deployed on the shoulder of a two lane freeway about 1,250 feet in advance of a work zone. The system consisted of a self contained battery powered trailer unit equipped with a speed radar and a 24-inch two digit LED speed display. The left lane was restricted and vehicles were merged into the right lane ahead of the work zone.
Pneumatic vehicle counter/classifiers were installed approximately 500 feet and 1500 feet in advance of the work zone lane closure in order to track vehicle speeds, speed distribution, and vehicle length before and after system deployment. Between August 18 and August 21, 1999, traffic data was collected to evaluate vehicle speeds "with" and "without" the radar warning sign in operation. Due to technical difficulties, the system was periodically disabled during the experiment and only 7 hours of "with" data were able to be collected. Thus, the before data, and the data collected while the unit was shut off were combined for a total of 58 hours of "without" data. In addition, only data collected during periods of uncongested flow (greater than 35 mi/h) were used in the evaluation.
The SpeedGuard system decreased driving speeds and increased speed uniformity as traffic approached the work zone. At a location 500 feet in advance of the lane closure taper, which was 750 feet downstream from the SpeedGuard system, the 85th-percentile speed and mean of the highest 15 percent of speeds were reduced significantly by about 5 mi/hr. The system effectively lowered the values of these parameters to speeds below or equal to the speed limit.