Verification and Efficacy of Automated Queue Detection Systems on Interstate Intelligent Work Zones

Intelligent work zones have been widely adopted in the United States because they have been proven to improve traffic safety and operations. One specific intelligent work zone system, known as automatic queue detection (AQD), is designed to measure work zone-related queueing in real time, and inform drivers upstream so they may be prepared to slow down or stop. This paper describes an evaluation of the performance and efficacy of four AQD systems implemented at work zones on Interstate 80 in Nebraska. Specifically, (i) the system performance was verified by examining whether the messages displayed on the portable dynamic message signs (PDMS) were consistent with the underlying AQD logic, and (ii) the system efficacy was measured by determining whether the overall speeds of individual vehicles and the space mean speed (SMS) were reduced when warning messages were provided. It was found that the AQD systems were functioning well as evidenced by an error rate of 0.7 to 2.3%. It was concluded that the SMS was reduced in response to the PDMS warning display indicating that there was slow or stopped traffic ahead. The decrease in SMS was found to be statistically significant and in the range of 3.5 to 7 mph. This was approximately 47% greater than the reduction in SMS that occurred when the PDMS did not display any message. In summary, it was found that the AQD systems were operating correctly and, more importantly, they were effective in reducing the speeds of the traffic stream downstream of the PDMS.