Toward the Development of Standards for Yellow Flashing Lights Used in Work Zones.

Flashing yellow warning lights are important for worker and driver safety in work zones. Current standards for these lights do not address whether and how they should be coordinated to provide course-way information to drivers navigating through work zones. A field study in which the intensities and flash patterns of warning lights along a simulated work zone were varied during daytime and nighttime, was conducted to assess drivers' responses to different configurations, leading to several conclusions. During the daytime, driver responses were relatively insensitive to warning light characteristics, although they preferred sequential and synchronized flash patterns over random, uncoordinated flashing. At nighttime, a temporal peak intensity of 25 cd with a sequential flash pattern was optimal for providing course-way information. A single initial warning light having a higher intensity may help drivers detect the work zone without creating unacceptable visual discomfort.