Trade-Off Between Delineation and Lighting on Freeway Interchanges

Abstract

DTFH61-85-C-00137The objective was to determine whether, with improved delineation, performance at partially lighted interchanges can approach performance under full lighting, particularly in rain. Two field studies were conducted. The first was to determine whether transient visual adaptation (TVA) influences detection on partially lighted interchanges and could interact with lighting. It was shown that TVA occurs under partial lighting and influences detection up to 600 feet from the last luminaire. The second field study was to determine the effect of lighting, weather, and improved delineation on driver performance. Data were obtained on two exits in dry and wet weather under full lighting with baseline delineation and three improved delineation systems. Partial lighting at one exit was with one luminaire, at the other with three luminaires. Findings support the contention that full lighting is superior to partial lighting in ramp speed-related measures. Analysis of delineation effects on ramp and spot speeds and on speed distributions showed few differences under dry conditions. In rain, effects were stronger but were neither large nor consistent enough to recommend improved delineation over the baseline system. Nonstatistical comparison of the results from two sited provided evidence that three-luminaire partial lighting was superior to single-luminaire. Performance on ramp segments downstream of the last luminaire suggested TVA influenced results