A study to measure the luminance of traffic signs at night with no appreciable glare sources within the field of view at certain distances and lateral positions ahead of a car was conducted on an unused airport runway by using capcalc, a new photometric measuring and analysis system. Yellow warning signs for curves and turns and yellow chevron signs were placed on the right or left side of a simulatedstraight, level, dry, two-lane rural highway. Three different typesof yellow sheeting materials (enclosed lens, encapsulated lens, andprismatic sheeting) with different reflectance values were used. The results of this study confirmed that the luminance of a reflectivetraffic sign observed by a driver at night illuminated by the beamsof the car is not a constant but changes according to an inverted u-shaped function as the distance between the car and the traffic sign ahead is increased. The observed luminance first increases with the distance between the car and the traffic sign ahead until about 400 ft and then decreases. The highest luminance values for the different lateral positions of the signs (right or left side of the road) are quite different; however, the patterns of the luminance curves as a function of the distance for the right side and the left side traffic signs are similar. Improvements to capcalc hardware are suggested. This paper appears in transportation research record no. 1316, Visibility for roadways, airways, and seaways 1991: proceedings of aconference, july 25-26, 1990, washington, d.C.
Abstract