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Work zone speeds have customarily been regulated by standard regulatory or advisory speed signs. However, most drivers do not slow down in response to these static speed control measures. The changeable message sign (CMS) with radar unit has dynamic capabilities which may be more effective in altering driver behavior. The radar, attached directly to the CMS, determines the actual speed of individual vehicles in the traffic stream. Upon detecting a speed higher than a preset threshold limit, the CMS can display a personalized warning message. This study evaluated the effectiveness of the CMS with radar unit in reducing work zone speeds. Four CMS messages designed to warn drivers that their speed exceeded the maximum safe speed were tested at seven work zones on two interstate highways in Virginia. Speed and volume data for the whole population traveling through the work zone were collected with automatic traffic counters. To assess the effect of CMS on high-speed drivers in particular, vehicles that triggered the radar-activated display were videotaped as they passed through 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 high-speed vehicles separately. Statistical tests were then conducted using these speed characteristics to determine whether significant reductions in speed accompanied the use of CMS. Odds ratios were first calculated to compare the odds for speeding when using CMS with the odds for speeding when using the Manual on Uniform Traffic Control Devices (MUTCD) signing only. These odds ratios indicated that CMS effectively reduced the number of vehicles speeding by any amount, by 5 mph or more, and by 10 mph or more in the work zone. When analysis of variance was used to compare speeds when using the CMS with speeds when using MUTCD signing only, all of the speed characteristics average speeds, 85th percentile speeds, speed variance, and the percentage of vehicles speeding by any amount, by 5 mph or more, and by 10 mph or more were reduced with any of the four CMS messages. In some cases, these reductions were not significant at a= 0.05. The messages were rated according to their level of effectiveness in the following order: [1] YOU ARE SPEEDING SLOW DOWN, [2] HIGH SPEED SLOW DOWN, [3] REDUCE SPEED IN WORK ZONE, and [4] EXCESSIVE SPEED SLOW DOWN. Finally, t tests were conducted using the speed data obtained for the high-speed vehicles, and at a significance level of ct 0.05, all of the messages were effective in significantly reducing the average speeds of those vehicles traveling 59 mph or faster in a 55 mph work zone when compared to MUTCD signing only.
"This synthesis will be of interest to traffic engineers in federal, state, provincial, and local transportation agencies who are responsible for the design and operation of safe and efficiency highway systems. It will also be useful to consulting traffic engineers, sign manufacturers, and vendors in the private sector who assist governmental clients in the application of changeable message sign (CMS) and other intelligent transportation systems (ITS) technology. It is an update of NCHRP Synthesis no. 61 (1979)."--Avant-propos.
Portable Changeable Message Sign (PCMS) systems used in work zones are programmable supplementary traffic control devices that display messages composed of letters, symbols or both and provide information and instructions to the traveling public approaching work zone activities. The study seeks to develop warrants and criteria for PCMS deployment in Illinois highway work zones. It is recommended that PCMS systems be used during long- and intermediate-term stationary work, for traffic control through incident areas, and in projects where advance-time notification is needed. The discussion focuses on spacing criteria, number of signs required, sign visibility and message legibility, text alignment, distance criteria, message length, duration and type, project-level operational guidelines, message storage and dissemination, repair, maintenance and utility costs, as well as control and coordination issues. The study concludes that additional research is needed in order to: develop a comprehensive standardized statewide database of messages and message abbreviations; develop a comprehensive repository with information about the technology of the various components of the PCMS units; coordinate PCMS units used in highway work zones with a corridor or regional ATMS system; and maintain information about the use of a PCMS unit in a work zone project and possibly integrate it with other relevant information in a management system.
In this report, researchers document the results of a laptop-based human factors study of alternative formats of presenting advance notice work zone information on portable changeable message signs (PCMSs) and a Texas Transportation Institute (TII) driving simulator study of the ability of motorists to capture and process information on two PCMSs used in sequence to convey information about upcoming traffic situations. Based on the studies, researchers recommend that messages that require the display of calendar dates for future roadwork and other traffic control activities should utilize a message format consisting of the three-character abbreviation of the month (e.g., APR for April) in conjunction with the date. When future work activities span several days all in the same month, the month needs be noted only once in the message (i.e., APR 21-23) rather than repeating the month (i.e., APR 21-APR 23). The ITI driver simulator study results indicate the need to keep overall messages at or below the four-unit maximum recommended in existing guidelines. Researchers found that presenting five units of information on sequential PCMSs resulted in low comprehension rates, below what would be acceptable for highway applications. However, by keeping the message length to four units, it does appear that the use of sequential PCMSs will result in comprehension rates comparable to those obtained by presenting the same information at a single location on a large dynamic message sign (DMS), and is recommended as an acceptable formatting approach for TxDOT. Comprehension may be enhanced by repeating one of the units of information on both PCMSs.
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