Determination of Optimal Intensities and Periods for Vehicle-Mounted Warning Lights Using Field Experiments

Increasing the safety of work zones and other locations where frontline service workers are present is important to reduce the potential for crashes involving passing vehicles and the workers. Flashing yellow warning beacons are often used to protect, delineate, and provide visual information to vehicles within and approaching work zones. Different intensities and flash frequencies of truck-mounted warning beacons allow drivers to identify front line service workers present outside of vehicles sooner. Field studies of workers (with and without reflective vests) present outside trucks were simulated to identify ideal combinations of warning beacon intensities and flash frequencies. This study determined that intensities of 25/2.5 cd and 150/15 cd provided the longest detection distance of the simulated worker. Although a flash frequency of 1 Hz resulted in the longest mean detection distance, this frequency was not statistically different from the 4 Hz flash frequency. Workers wearing reflective vests were seen the furthest distance away from the trucks for all combinations of intensity and flash frequency.