CONSPICUITY OF RETROREFLECTIVE SIGNS AND DEVICES AT NIGHT WHEN DRIVING WITH ONLY ONE HEADLAMP WORKING

A study was performed with a Macintosh microcomputer to analytically assess the effects of driving with only one headlamp working (driver side or passenger side, European lowbeam, American H6054 lowbeam, and American H6054 highbeam) and the effects of misaim of the one headlamp working on the conspicuity of retroreflectorized warning signs and devices of different brightnesses at night on a straight and a left-curved section of a highway. The computer model used computes all the geometric distances and angles necessary for a selected situation involving driver, vehicle, and reflectorized target, the amount of illumination returned to the driver's eyes for selected retroreflective materials, environmental and vehicle conditions, and a multiple of the visual laboratory detection threshold value. Geometric and photometric calculations were performed for a number of selected situations involving driver, vehicle, environmental conditions, retroreflective materials, and only one headlamp working with misaim. Results show that driving with only one headlamp working can have a significant detrimental effect on the visual detection distances for reflectorized targets, especially under certain headlamp misaim conditions. Therefore, it appears to be important for manufaturers to design and produce headlamp systems and headlamps with the highest possible reliability and the longest possible headlamp life (subject to economic feasibility), to have a strict law enforcement policy (encouraging immediate headlamp replacement) aimed at drivers driving vehicles at night that have only one headlamp working, and to possibly increase the minimum required brightness level of the reflective materials used for reflectorized warning signs and devices to at least partially offset the detrimental effect on visual detection distances for a driver driving with only one headlamp working.