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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 suggested 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 to other caution displays. However, additional research was needed to confirm these findings. The Utah Department of Transportation 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 diamond was associated with a statistically significant 3 km/h (2 mph) reduction in mean speeds, whereas the flashing box display was associated with no statistically significant reduction in mean speeds, indicating that the dancing diamonds prompt safety near highway work better 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 one, 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.