Reflective Properties of Selected Road Surfaces for an Automobile Headlamp Geometry

Abstract

Luminance-contrast-based pavement marking visibility models are widely used in the design of street and automobile lighting systems, the design and evaluation of retroreflective sheeting materials and pavement-marking materials, and in the establishment of minimum visibility requirements for nighttime motorists. Computer-based visibility models usually determine the visibility of pavement markings by comparing the available luminance contrast formed between the pavement marking and the immediate surrounding road surface with a human threshold contrast value. However, to be able to calculate the luminance contrast between a pavement marking and the road surface, a pavement-marking visibility model needs matrices of retroreflectance as a function of the entrance angle and the observation angle, both for the pavement and the pavement markings. However, no extensive field data are available on the reflective properties of road surfaces under an automobile headlamp geometry (observation angles less than 1°). Retroreflectance matrices were developed for old asphalt, new asphalt, old concrete, and new concrete road surfaces. The road surface retroreflectance was measured with a specially designed apparatus in the field. Multiple linear regression models were developed with the retroreflectance data obtained for each measured road surface. Traffic sign luminance measurements under automobile headlamp illumination conditions were conducted in the field at night to determine the degree to which a post-mounted traffic sign (sign center 1.98 m above the ground) receives indirect light reflected from the road surface.