An analytical study was conducted on a microcomputer to assess the effects of misaimed low beams and high beams on the visual detection of reflectorized targets of different brightness, such as reflectorized warning signs, overhead guide signs, license plates, and post delineators. The study was done at night, on a straight and a left-curved section of highway. The model used computed all the geometric distances and angles necessary for a selected driver-vehicle-reflectorized target situation for each headlamp, the amount of beam illumination that is returned to a driver's eyes for selected environmental and vehicle conditions, and a multiples of threshold value. Calculations were performed for a matrix containing 25 passenger-side and driver-side beam misaim combinations (5 x 5 points, identical and nonidentical misaims). The results show that both vertical and horizontal beam misaim may have a detrimental effect upon the detection distance of reflectorized targets in the driving environment: however, the use of brighter retroreflective materials can help to offset the detrimental distance effect in most cases. This paper appears in transportation research record no. 1247, Visibility criteria for signs, signals, and roadway lighting.
Abstract