Public Perception of Pavement-Marking Brightness

Abstract

The Minnesota Department of Transportation (MnDOT) conducted research to establish a threshold value of retroreflectivity for use in its pavement-marking management program. Members of the general public were invited to drive MnDOT automobiles on a driving course of state and county roads. An interviewer rode along with each study participant asking questions about the brightness (or luminance) of pavement markings within predetermined sections of roadway. The interview was conducted after dark with the car’s headlights at low beam. For each section of roadway, study participants were asked to grade the visibility of the pavement markings; the edge line and the centerline were evaluated individually. The average scores received from all study participants for a specific section were compared with retroreflectivity data taken by MnDOT’s mobile retroreflectometer. Analysis of the data revealed an apparent correlation between the readings taken by the retroreflectometer and the rating scores provided by the study participants. This analysis also suggested that the threshold value of acceptable retroreflectivity versus unacceptable retroreflectivity was between 80 and 120 mcd/m2/lx when using the Laserlux® retroreflectometer. In its continuing effort to improve “customer service,” MnDOT has committed to providing durable pavement markings that are visible year-round and is purchasing equipment and training personnel to implement this program. As a result of the market research project, MnDOT will use 120 mcd/m2/lx as the threshold between acceptable retroreflectivity and unacceptable retroreflectivity when developing the new pavement-marking management program. The establishment of a threshold retroreflectivity value also will allow cost-benefit and life-cycle analyses of different pavement-marking materials and help MnDOT to grade itself on how well it is meeting customer expectations.