Members of the general public were invited to drive Mn/DOT automobiles on a driving course comprised of State and County roads. An interviewer rode along with each study participant asking questions about the brightness of pavement markings within predetermined sections of roadway. The interview was conducted after dark with the car's headlights kept 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 each evaluated individually. The average score received from all of the study participants for a specific section were compared with retroreflectivity data taken by Mn/DOT's mobile and handheld reflectometers.
Analysis of the data revealed a significant correlation between the readings taken by the reflectometers and the rating scores provided by the study participants. This analysis suggests that the threshold value of acceptability versus unacceptability is between 80 and 120 Mcd/m2/lux.
This establishment of a threshold retroreflectivity value(s) will allow cost-benefit/lifecycle analysis of different materials, and allow Mn/DOT to grade itself on how well it is meeting 'customer expectations'.
