Daniel B. Fambro student paper award: dancing diamonds in highway work zones: an evaluation of arrow panel caution displays

Arrow panels, consisting of a matrix of lights, symbolically convey additional warning to motorists. Nondirectional arrow panel displays are designated as caution displays. Before 2001, literature lacked significant statistical support for any one type of caution display. A 2001 Oregon Department of Transportation (ODOT) study suggests that the Dancing Diamonds display performs in the field as well as, if not better than, other caution displays. ODOT also found that local citizens preferred the Dancing Diamonds over other caution displays. However, additional research was needed to confirm these findings. The Utah Department of Transportation (UDOT) has used the Dancing Diamonds display since June 1972. To evaluate the effectiveness of the Dancing Diamonds and Flashing Box displays a field experiment was conducted. The results of this experiment show that the Dancing Diamonds was associated with a statistically significant 3 kph (2 mph) reduction in mean speeds, whereas the Flashing Box display was associated with no statistically significant reduction in mean speeds, indicating indicates that the Dancing Diamonds prompts safety near highway work than the Flashing Box. A comprehension/opinion survey was also conducted. Regardless of caution display type, most of the 412 respondents would “slow down” upon seeing any caution display, and they understood the meaning of the display to be “use caution ahead. ” Fifty-four percent of drivers thought that use of the Dancing Diamonds would best prompt safe driving, followed by the Flashing Diamonds (43%) and the Flashing Box (3%). For getting attention, 94% said the Flashing Box was the least effective. TRB 2003 Annual Meeting CD-ROM Paper revised from original submittal. B. M. Turley, M. Saito, S. Sherman 2 DANCING DIAMONDS IN HIGHWAY WORK ZONES: AN EVALUATION OF ARROW PANEL CAUTION DISPLAYS INTRODUCTION Arrow panels have been widely used in highway work zones for the past twenty-five years. These panels are signs consisting of a matrix of lights that convey additional warning and direction symbolically to motorists. This matrix of lights is capable of flashing directional displays as well as nondirectional displays. Directional displays, such as “Flashing Arrow” and “Sequential Chevron,” have been effectively used to aid drivers in switching lanes. Directional guidance is the main purpose of arrow panels. However, to maximize safety per dollar of investment, a nondirectional “caution” display has also been used. This caution display is the only nondirectional arrow panel display authorized by the current Manual on Uniform Traffic Control Devices (MUTCD) and is designated “Flashing Caution” (1). The purpose of the caution display is to increase safety near highway work. Caution displays provide additional warning to drivers, so that they may exercise caution while traveling through an upcoming work zone. Safely slowing down, switching lanes on a multilane highway, and being more alert are all acceptable forms of exercising caution. The caution display is currently designated for shoulder work operations and lane closures on a two-lane, two-way highway (1). Unlike all other arrow panel displays, the caution mode never requires the driver to make a lane change. Even when used at a temporarily closed lane of a two-lane, two-way highway, the caution display is meant only to alert the driver and to call attention to the other traffic-control devices. Figure 1 shows the various caution display types. Before the MUTCD 2000 edition, the Flashing Box and Bar were suggested, but any “caution mode consist[ing] of four or more lamps” which “did not indicate a direction” was permitted (2). The Flashing Box and Bar have been used throughout the United States. The Dancing Diamonds pattern has been used in the western states, such as Utah and Oregon. The Utah Department of Transportation (UDOT) has used the Dancing Diamonds display since June 1972 on state funded projects. The Alternating TwoCorner display has been studied in the past, but to the authors’ knowledge has not been used. The Flashing Diamonds pattern was proposed recently by the Utah Department of Transportation (UDOT). The main purpose of this research is to evaluate the effectiveness of the Dancing Diamonds caution display as compared with the standard Flashing Box caution display. A brief literature review was first performed. Second, a field experiment was conducted to gather actual driver responses to caution displays. Third, a TRB 2003 Annual Meeting CD-ROM Paper revised from original submittal. B. M. Turley, M. Saito, S. Sherman 3 comprehension/opinion survey was conducted to measure driver comprehension of caution displays as well as gather opinions concerning caution displays. At UDOT’s request, consideration for the Flashing Diamonds was added midway through this research and, consequently, is analyzed in the comprehension/opinion survey only. These three areas of research are discussed in the paper. The study yielded the following conclusions: (1) there was insufficient past research on which to base caution displays standards; (2) the Dancing Diamonds display was associated with cautious driving, whereas the Flashing Box display seems to have little effect on drivers; (3) there was little difference in driver comprehension between the Dancing Diamonds, Flashing Diamonds, and Flashing Box displays; however, a majority of respondents felt that the Dancing Diamonds display best prompted safety near highway work. LITERATURE REVIEW Non-directional caution displays have not been studied exclusively until recently. This review first focuses on past research, which is the foundation for current standards. In past research, caution displays were appendages to broader research on directional displays. Consequently, only the caution display segments of that research were examined. Second, this review looked at recent Oregon Department of Transportation (ODOT) research (3), which focuses specifically on caution displays. ODOT’s research and evidence suggested that some caution display types were more effective than others. Past Research A December 1978 Federal Highway Administration (FHWA) report consists of two separate studies: a human factors study and a field study (4). This study is accompanied by a set of recommendations.