Quantitative versus Qualitative Assessment of Pavement Marking Visibility

Abstract

Many state departments of transportation (DOTs) often use a subjective evaluation program to assess the condition of their roadway assets. Because pavement markings are typically only a small part of these assessment programs and because visual assessment is subjective, the ratings may not always be accurate in identifying roadways with inadequate markings. This research sought to evaluate the accuracy of visual assessments of pavement markings. The Texas Transportation Institute conducted two separate nighttime evaluations as part of a Texas DOT research project. The first evaluation was conducted on open roads, and the second was conducted on a closed experimental course. Subjective rating data were collected on pavement markings by several DOT evaluators. To analyze the data, researchers compared retroreflectivity measurements with subjective ratings of the pavement markings. For the first night study, the average subjective rating of each marking compared with the measured retroreflectivity resulted in a logarithmic R2 value of .818. The second night study resulted in a logarithmic R2 value of .821 before training and .809 after training. The data were also evaluated by marking color and evaluator experience level. Researchers found that average subjective ratings showed acceptable correlation with retroreflectivity measurements, but ratings could show large variations between individuals. The researchers recommend that subjective assessment be considered a viable option for evaluating pavement markings. They also recommend that for any assessment the evaluator be well trained or multiple evaluators be utilized, with reported ratings averaged to provide reliable results.