CORRECTING ROADWAY LIGHTING DESIGNED BY LUMINANCE AND SMALL TARGET VISIBILITY METHODS FOR VARIATIONS IN HIGHWAY GEOMETRY

摘要

This paper examines the relationship between horizontal and vertical highway geometryrnand the calculation of pavement luminance. Luminance is the primary design parameter used to designrnroadway lighting (King, 1972). Whether using luminance design or the STV variant, lighting engineersrnassume that the surface of the road is flat. This is always incorrect as the pavement’s surface is alwaysrncrowned for drainage, even on level stretches of road. The effect of this assumption becomes even morernmarked on superelevated curves. Thus, correction factors must be applied to luminance calculations tornallow for the changes in the angle of reflection used to compute the design values of luminance in bothrnthese methods. The paper concludes that neglecting the effect of highway geometry can introduce anrnerror of up to 24% in luminance calculations in areas where safety lighting is important such asrnsuperelevated entrance and exit ramps on freeways. It also presents a table of correction factors for usernin roadway lighting design.