Refinement of Drivers' Visibility Needs during Wet Night Conditions

Abstract

The purpose of this project was to develop a specification for the minimum retroreflectivity of pavement markings in wet nighttime conditions. For this specification to be established, the performance of four retroreflective pavement marking materials in wet night conditions was evaluated. The performance of the pavement markings was evaluated by driver participants under simulated rain conditions with a protocol similar to that of studies that had already been performed at the Virginia Tech Transportation Institute, Virginia Polytechnic Institute and State University. The performance of the markings was verified on the basis of the participants' ability to detect the end points of the markings in both rainy and clear conditions. This investigation reached the following conclusions: (a) The materials developed over recent years showed an improved performance over those tested previously. (b) The log-linear relationship found previously was functional for the data provided. Two models were developed. The model with no intercept provided a more constrictive boundary at low levels of retroreflectivity. (c) A retroreflectivity value above 250 millicandelas per square meter per lux (mcd/m2/lx) provided limited return in terms of detection distance. (d) A specification limit of 150 mcd/m2/lx provided adequate visibility for 55 mph in dry conditions and 40 mph in wet conditions with standard dry retroreflectivity measurements and 1 in./h measurements for wet conditions. This value should be the minimum maintained over the life of the marking. (e) The retroreflectivity specifications for a white and a yellow material should be equal. (f) The rumble stripe showed a significant recovery time improvement over the other tested materials. A minimum retroreflectivity of 150 mcd/m2/lx for white and yellow pavement markings in both dry and wet nighttime conditions is recommended.