This study was designed to evaluate the effectiveness of the CMS, changeable message sign, with radar unit in reducing speeds in the work zone. Four particular messages, designed to warn drivers that their speed exceeded the maximum safe speed, were tested on the CMS at seven work zones on two interstate highways in Virginia. Speed and volume data for the whole population travelling through the work zone were collected with automatic traffic counters. In addition, in order to assess the effect of the CMS on high-speed drivers in particular, vehicles that triggered the radar-activated display were videotaped as they progressed trough the work zone. Using the data obtained from the traffic counters and videotapes, speed characteristics were determined at the beginning, middle, and end of the work zone. These characteristics were computed for the whole population and for the high-speed vehicles separately. Statistical tests were then conducted using these speed characteristics in order to determine whether there were significant reductions in speeds as a result of using the CMS. Odds ratios were calculated to compare the odds for speeding when using the CMS with the odds for speeding when using the Manual on Uniform Control Devices (MUTCD) signing only. These odds ratios indicated that the CMS is an effective means of reducing the number of vehicles speeding in the work zone by any amount, by 5 mph or more, and by 10 mph or more. T tests were also conducted using the speed data obtained for the high-speed vehicles, and at a significance level of a = .05, it was found that allof the messages were effective in significantly reducing the average speeds of those vehicles travelling 50 mph or faster in a 55 mph work zone when compared to vehicle speeds when using MUTCD signing only. (A)
Abstract