Portable Changeable Message Signs Research Articles

Driver responses to graphic-aided portable changeable message signs in highway work zones

ABSTRACTPortable changeable message signs (PCMSs) have been employed in highway work zones as temporary traffic control devices. Various studies showed that adding graphics to PCMS messages can provide advantages to traditional text messages, such as increasing legibility and improving the understanding of elderly drivers. This article synthesizes the findings of a two-phase research project aimed to investigate driver responses to graphic-aided PCMSs. Different text and graphic-aided PCMSs representing roadwork and flagger were set up in the upstream of highway work zones, and speed data of more than 2,700 vehicles were collected with a series of five speed sensors to determine vehicle speed reduction. Nearly 1,000 onsite driver surveys were performed to identify driver preference on the added graphics. The results discovered that graphic-aided PCMSs reduced mean vehicle speed between 13% and 17% and reduced the speed of passenger cars and trucks significantly differently depending on their locations in work zone. The results indicated that all drivers correctly interpreted the flagger graphic and two work-zone graphics, and suggested that 52% to 71% of drivers preferred to see graphics in PCMS messages. The findings also revealed that driver age did not have a significant impact on driver preference on PCMS message format.

A driving simulator study to analyze the effects of portable changeable message signs on mean speeds of drivers

ABSTRACTIn the United States, between 2003 and 2012, excessive speed was a contributing factor in about one third of all fatal crashes. Intelligent transportation systems (ITS) with the potential to reduce speed and thereby improve safety are therefore of considerable interest. In this article, the mean speeds of drivers affected as a result of four different messages displayed on portable changeable message signs (PCMS) evaluated in an advance-warning area of a work zone are presented. A systematic examination of the combined effects of four sequentially placed PCMS was conducted using a driving simulator (DS). The four messages investigated include speed, state of traffic downstream, and the travel times to exit the work zone. The message sign “Prepare to Stop/Stopped Traffic Ahead” showed the largest reduction in speed relative to the other messages at a location just upstream of the lane closure. The message also showed the largest overall reduction (30.3 mph, 44.1%) in mean speed compared to a control scenario. Greatest impact on drivers' mean speeds was therefore observed resultant of a strong and clearly worded message. A post-DS experiment survey indicated drivers' ranked the message “Speed Ahead 30 mph/X Min To End of WZ” as most effective. The drivers complied closely with this message as the mean and 85th percentile speeds were 26.5 and 30.7 mph, respectively, at a location just upstream of the lane closure. This message also showed the second largest overall reduction (26.3 mph, 38.2%) in mean speed compared to a control scenario. The overall reduction in mean speeds was resultant of combined effects of four PCMS in a work zone.

Safety Effects of Portable End-of-Queue Warning System Deployments at Texas Work Zones

The reduction of upstream end-of-queue (EOQ) crashes at work zone lane closures has been a focus of the Texas Department of Transportation, Austin, for several years. An ongoing widening effort on Interstate 35 through central Texas prompted officials to examine and implement technologies to mitigate the impacts of EOQ warning crashes. An EOQ warning system was established, which consisted of a highly portable work zone intelligent transportation system of easily deployable radar speed sensors linked to one or more portable changeable message signs and highly portable transverse rumble strips. The EOQ system was deployed upstream of nighttime lane closures, where queues were expected to develop. Although the sample sizes were relatively small, the trends did suggest that the systems were having a positive effect to reduce crashes. Overall, the EOQ warning system was estimated to have reduced crashes 44% from what they otherwise would have been if the system had not been used. The crashes that did occur were less severe, which was most likely because fewer of them were of the high-speed, rear-end-collision variety. With traditional societal crash cost values updated to 2014 dollars, the use of the EOQ warning system at nighttime lane closures reduced crash costs by $1.36 million over the analysis period. This figure equated to $6,313 in crash cost savings per night of deployment. Compared with the approximate costs of procurement and deployment of these systems, a break-even point was achieved after 95 to 190 nights of use.

Impact of Advisory Signs on Vehicle Speeds in Highway Nighttime Paving Project Work Zones

Pavement preservation projects typically require construction workers to conduct their work in close proximity to ongoing traffic. During paving operations, workers are located within a protected work zone. Some are situated nearby or engaged with the equipment, while others may be a long distance from the equipment and on foot. The study reported here was conducted to investigate how temporary advisory speed signs located periodically in a work zone affected vehicle speeds within highway paving project work zones. The study used an experimental approach that involved a multilane paving project on a high-speed roadway in Oregon. The posted regulatory speed on the roadway was 65 mph, which was reduced temporarily to 50 mph in the work zone. During construction, 35 mph advisory signs were posted along with other traffic control devices (e.g., “Speed 50” signs with radar speed display and portable changeable message signs on rollers), and the impact they had on vehicle speed and speed variability was evaluated. The research findings indicated that use of the 35 mph signs led to lower vehicle speeds within the work zone. The reduction in speed was greater by passenger cars than by trucks. The use of 35 mph advisory signs in work zones is recommended to help reduce vehicle speeds through the entire work zone and to minimize safety risks, especially to workers on foot and situated away from major equipment.

Effectiveness of graphic-aided portable changeable message signs in reducing vehicle speeds in highway work zones

Portable changeable message signs (PCMSs) have been employed in highway work zones as a temporary traffic control device for decades in the United States. Results of previous research showed that the traditional text-based PCMS had several limitations, such as having a short range of legibility and being difficult to read by elderly and non-English-speaking drivers. A few simulation studies indicated that using graphic-aided PCMSs could likely overcome these limitations. This paper presents the results of field experiments that were conducted to determine the effectiveness of graphic-aided PCMS in reducing vehicle speeds in the upstream of highway work zones. In field experiment Phase I, a full-matrix PCMS was programmed to display a work zone graphic and a flagger graphic, which were similar to the W21-1 sign and W20-7 sign, respectively, specified by the Manual on Uniform Traffic Control Devices. In field experiment Phase II, the PCMS was programmed to display two alternative work zone graphics along with the original work zone graphic. 1115 and 1600 valid vehicle speed data were collected during field experiments Phase I and Phase II, respectively. The results of data analysis suggested that graphic-aided PCMSs reduced mean vehicle speeds between 13% and 17% in the upstream of a work zone. This study provided valuable knowledge to government agencies and the transportation industry on how to regulate and implement graphic-aided PCMS in highway work zones.

Hybrid Work Zone Information System with Portable Changeable Message Signs and Dedicated Short-Range Communication

The future deployment of dedicated short-range communication (DSRC) technology requires that applications with their bases in DSRC be integrated with existing traffic management techniques so that vehicles not equipped with DSRC at the early stage of DSRC deployment can also reap the potential benefits of DSRC technology. A hybrid traffic information system was successfully developed; it combines DSRC technology and portable changeable message signs (PCMSs) for use in the work zone environment to improve traffic mobility and thereby driver safety. The developed system uses DSRC-based vehicle-to-infrastructure and vehicle-to-vehicle communication to acquire travel safety parameters, such as travel time (TT) and the starting location of congestion (SLoC), and to disseminate these parameters to DSRC-equipped vehicles and PCMSs, which are strategically placed along the roadside. Through the use of the DSRC-PCMS interface developed and demonstrated in this work, PCMSs can receive these travel safety parameters from nearby DSRC-equipped vehicles on the road through DSRC-based vehicle-to-vehicle communication, and display them for the drivers of vehicles that lack DSRC capability. Such a system can be useful during the early stage of DSRC deployment when DSRC market penetration is low. In addition, a rigorous analysis was conducted to investigate the minimum DSRC market penetration rate needed for successful functionality of the developed system with respect to both acquisition and dissemination of TT and SLoC. Through the use of a realistic traffic flow model, guidelines were developed to estimate a minimum DSRC penetration rate needed to deploy the developed system for a variety of traffic scenarios on a given work zone road.

Driver Behavior and Preferences for Changeable Message Signs and Variable Speed Limits in Reduced Visibility Conditions

This article investigates the factors affecting drivers’ stated behavior in adverse visibility conditions and examines whether drivers rely on and follow advisory or warning messages displayed on portable changeable message signs (CMS) and/or variable speed limit (VSL) signs in different visibility and traffic conditions, and on two types of roadways: freeways and two-lane roads. A multiple-approach survey was designed to collect opinions and stated data from Central Florida drivers. Categorical data analysis techniques such as conditional distribution, odds ratio, and chi-squared tests were applied. In addition, two modeling approaches, bivariate and multivariate probit models, were estimated. The results revealed that gender, age, road type, visibility condition, and familiarity with VSL sign were the significant factors affecting the stated likelihood of reducing speed following CMS/VSL instructions in reduced visibility conditions. Other objectives of this study were to determine the content of messages that would achieve the best perceived safety and drivers’ compliance and to examine the best way to improve safety during these adverse visibility conditions. The results indicated that respondents thought that “Caution–fog ahead–reduce speed” was the best message and that using that CMS and VSL signs together was the best way to improve safety during such inclement weather situations. Based on the findings of the present study, several recommendations are suggested as guidelines to improve safety in reduced visibility conditions.

Motorist Understanding of Alternative Displays for Speed Limits in Work Zones

In Texas, speed limits for short-term work zones are reduced speed limits that are posted only when work activity is present. When work activity is not present, the reduced speed limit signs are to be removed or covered; the legal speed limit for that segment reverts to the normal zone speed limit. The major challenge of speed limits for short-term work zones is the daily process of installing and removing, or uncovering and covering, signs. In this study, researchers conducted a laptop-based laboratory survey to determine (a) motorists' understanding and opinions of alternative short-term signs for speed limits in work zones and the enforceability of limits, (b) the success of the orange or white light-emitting diode (LED) color used on electronic speed limit (ESL) signs and portable changeable message signs (PCMSs) in indicating to motorists that they were advisory or regulatory signs, and (c) motorists' preference for short-term speed limit displays. The four categories of signs included in the survey were static work zone signs, ESL signs, speed limits displayed on PCMSs, and “Your Speed” signs (distracters). On the basis of the results obtained from this survey, researchers recommend the use of ESL signs and flexible roll-up signs for speed limits in static work zones for displaying speed limits in short-term work zones. To ensure that the speed limit displayed on ESL signs is considered a regulatory speed limit, the changeable display should be composed of white LEDs.

Driver Understanding of Sequential Portable Changeable Message Signs in Work Zones

Results of a Texas Transportation Institute driving simulator study are presented. The study's focus was the ability of motorists to capture and process information on two portable changeable message signs (PCMS) used in sequence (i.e., one PCMS following another along the edge of the roadway such that each PCMS contains part of a single message). The purpose of the PCMS is to convey information about upcoming traffic situations. Results indicate the need to keep messages at or below the four-unit maximum recommended in existing guidelines. It was found that presenting five units of information on sequential PCMS resulted in low comprehension rates, below what would be acceptable for highway applications. However, by keeping the message length to four units, it appears that the use of the sequential PCMS will result in comprehension rates comparable with those obtained by presenting the same information at a single location on a large dynamic message sign. Comprehension may be enhanced by repeating one line of the message on both PCMS used in a given sequence.

Evaluation of Alternative Dates for Advance Notification on Portable Changeable Message Signs in Work Zones

Results of a laptop-based human factors study of alternative formats of presenting notice of future roadwork messages on portable changeable message signs (PCMS) in highway work zones are documented. A total of 192 participants across Texas were shown a series of different two-phase messages for a fixed period of time and asked questions by test administrators to determine comprehension and recall of the information presented in each message. Participants were also asked to indicate their preferred format for presenting such information on a PCMS. On the basis of these studies, it is recommended that messages that require the display of calendar dates for future roadwork and other traffic control activities use 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 in the same month, the month needs to be noted only once in the message (i.e., APR 21–23) rather than repeating the month (i.e., APR 21-APR 23).

Automated Work Zone Information System on Urban Freeway Rehabilitation

In October 2004, about 9 lane km of deteriorated truck lanes on Interstate 15 at Devore in Southern California was rebuilt during 18 days with extended one roadbed full-closures with the counterflow traffic system and 24-h construction operations. The project implemented the automated work zone information system (AWIS) to reduce peak hour delay during construction by changing road user's travel patterns and diverting traffic to detour routes. This paper describes the design, performance, and validation of AWIS with monitored traffic data before and during construction used. The AWIS was installed to provide road users with real-time travel information so that they could avoid traffic delays in the construction work zone (CWZ) corridor. Travel times through the CWZ were estimated from speed data and enhanced in two ways: ( a) portable and permanent changeable message signs on site and ( b) off-site (project website) implementation with travel time messages, traffic snapshots, and video streaming. AWIS travel time was estimated at 90% of actual travel times as measured by probe vehicles. The peak hour traffic demand through the CWZ was reduced by up to 18%, with significant volume increases to detour freeways. The AWIS operation contributed to a decrease in the maximum delay for weekday peak hours (from expected 90 min to measured 50 min on average during construction). The outcome of this study will help transportation agencies and practitioners efficiently design and operate AWIS for highway rehabilitation under high traffic volume.

Deployment of Smart Work Zone Technology in Arkansas

The Arkansas State Highway and Transportation Department began an extensive pavement rehabilitation program in the spring of 2000 that ultimately will rebuild approximately 380 mi, or 60%, of Arkansas’ total Interstate miles. To improve safety and manage congestion in work zones, the department has deployed smart work zone technology systems on five projects. The main goal for this endeavor was to provide a queue-detection system that will prevent or reduce rear-end collisions and will also provide motorists with real-time information about potential backups caused by lane closures. After each system was installed, a general evaluation of the basic design was conducted. Knowledge gained was applied to each subsequent system, to improve the design and to provide increased effectiveness, reliability, and practicality. The design evolution of these systems is presented, the design development is discussed in detail, and the effectiveness of two of the automated work zone information systems installed on Interstate rehabilitation projects in Arkansas is evaluated. The systems used were ADAPTIR from Scientex Corporation and CHIPS from ASTI Transportation Systems. These systems included all hardware, software, and other equipment necessary for collecting, displaying, and processing traffic condition data. These data were used to provide motorists with real-time speed-control, delay, and diversion advisory messages via portable changeable message signs and a highway advisory radio system.

Guidelines for Application of Portable Work Zone Intelligent Transportation Systems

Work zone intelligent transportation systems (WZITSs) are promoted as a way to improve safety and reduce congestion at work zone locations where traditional traffic management centers do not exist. These systems usually integrate portable changeable message signs and speed sensors with a central control system that automatically determines appropriate messages that are based on current traffic conditions. Manufacturers of these systems claim that WZITSs can warn drivers of downstream congestion, alert drivers to slower speeds ahead, and suggest alternate routes on the basis of prevailing conditions. Transportation agencies are often asked to make decisions on the installation of a WZITS without the benefit of objective information on its expected performance. Relatively few operational tests of these systems have been performed, and the results are not always well documented or conclusive. Agencies need guidance to help them determine whether a WZITS system would improve safety and operations at a specific site. Applications of WZITSs are reviewed, and a series of guidelines for their deployment, based on lessons learned from past tests, is presented.

Effectiveness of Condition-Responsive Advisory Speed Messages in Rural Freeway Work Zones

Condition-responsive advisory speed messages were evaluated as part of the Midwest States Smart Work Zone Deployment Initiative, a pooled-fund study sponsored by Iowa, Kansas, Missouri, Nebraska, and FHWA. The messages were displayed on three portable changeable message signs (PCMS) placed approximately 1.61 km (1 mi), 4.83 km (3 mi), and 12.87 km (8 mi) ahead of a work zone on a rural interstate highway in Nebraska. The messages were intended to advise drivers of the speed of slower traffic ahead and thereby encourage them to slow down. Speeds downstream of the PCMSs were measured and compared with the speeds displayed in the messages. The results of the analysis indicate that the messages were somewhat effective in reducing speeds. Their effectiveness could have been improved if the distances between the PCMSs had been shorter and thus the message locations would have been closer to the points with lower traffic speeds. Driver interviews revealed that the advisory speed messages were understood and thought to be useful by most drivers who had seen them. However, some drivers questioned their usefulness and doubted their reliability, because they had not seen any reason to slow down.

Changeable Message Sign Messages for Work Zones: Time of Day, Days of Week, and Month Dates

The New Jersey Department of Transportation initiated a research study designed in part to further the state of knowledge of changeable message sign message design with specific application to the needs in New Jersey. Laboratory studies of human factors are described here; the studies were conducted in New Jersey to evaluate shorter alternative messages than those currently used to display time of day, days of week, and calendar dates. These types of messages are often displayed on portable changeable message signs used in highway work zones. Among the findings were that a dash can be used instead of the term Thru to indicate roadwork for a range of successive days; the term Weekend is not a good descriptor for work that begins on Friday evening and ends on Monday morning; the term Days did not connote specific daytime, off-peak times for roadwork, but it may be satisfactory for certain time periods; likewise, the term Nights did not connote specific nighttime, off-peak times for roadwork, but it may be satisfactory for certain time periods; Nite is an acceptable substitute for Night; and calendar dates were not easily translated by drivers to specific days of the week.

Driver Understanding of Abbreviations on Changeable Message Signs in New Jersey

The objectives of this research were to evaluate abbreviations currently used on changeable message signs (CMSs) in New Jersey and develop new abbreviations specific to the needs of New Jersey transportation agencies. A special emphasis was on developing abbreviated phrases that could be displayed on portable CMSs that have only eight characters per line. Human factors laboratory studies were conducted in both New Jersey and Texas in which a list of abbreviations was given to drivers, who were asked to write down the meanings. The results revealed that a group of 18 abbreviations was quite well understood by New Jersey drivers and met the acceptability criterion of 85 percent of the drivers surveyed. Other abbreviations were understood by 75 to 84 percent of New Jersey drivers, and it will require an extensive educational effort before they can be used on CMSs. Some of the abbreviations were considered unacceptable. There were regional differences with respect to driver understanding of some of the abbreviations. Proper noun abbreviations were found that were understood by 85 percent or more of the drivers tested in New Jersey. As expected, there were regional differences in New Jersey. Generally, the proper noun abbreviations were understood better by drivers who live in the part of the state where the facility or structure is located whose name was abbreviated.