Texas Transportation Institue

A member of The Texas A&M University System, the TTI (Texas Transportation Institute) has, since 1950 developed solutions to the problems and challenges facing all modes of transportation.

Over the last 15 years, researchers at the Texas A&M Transportation Institute (TTI) have established a comprehensive research program related to the visibility of traffic signs and pavement markings. Their researchers have conducted numerous studies to evaluate how well drivers can see signs and markings, both during the day and at night and how transportation agencies can improve signs and markings to meet the needs of drivers and other transportation agencies striving to build, maintain and enhance roadways in the United States. TTI research in this area cuts across other important areas of transportation research—older driver issues, work zone safety, and larger vehicle considerations—all are part of the picture when it comes to “seeing the road.”

Mobile Retroreflectometer Certification Program

The TTi runs a mobile retroreflectometer certification program which provides a quantitative basis for evaluating the ability of a contractor to accurately measure the retroreflectivity of long-line pavement markings. A contractor who wishes to be eligible to work on TXDOT (Texas Department of Transportation) contracts that utilize mobile retroreflectivity measurements must apply to the TTI first for certification.

RetroTek-MU Mobile Pavement Marking Retroreflectometer Evaluation by Texas A&M Transportation Institute

Report prepared by Adam Pike, P.E. Associate Research Engineer, Texas A&M Transportation Institute, College Station, Texas

Summary of Findings:

This testing was designed to evaluate the accuracy of the RetroTek-MU mobile pavement marking retroreflectometer across a range of factors. These factors are typically encountered during data collection and their impact needs to be minimized to have a system that can continually collect accurate retroreflectivity data across a range of pavement markings in various conditions. The testing included 42 tests on 91 pavement marking segments over a variety of road segments to evaluate the mobile retroreflectometers performance.

The open road testing evaluated typical road surfaces and pavement markings in typical data collection conditions. Overall the retroreflectivity trend along the test sections was consistent between the RetroTek-MU and the portable retroreflectometer with an R2 value of 0.9417. The average systematic error was −5.7 percent with an average random error of 8.7 percent. The results indicate that when considering marking color or marking pattern the error was approximately 11 percent or less. The measurements at the left or right in-lane
positions differed by approximately 10 percent or less when compared to the center of the lane
position. The low RL calibration level resulted in data that were between 6 and 9 percent lower on
average than data collected with the high RL calibration setting.

The closed course testing results indicated that the majority of the mobile data were within 10 percent of the portable data. The average systematic error was 0.9 percent, with an average random error of 5.7 percent. Overall the retroreflectivity trend along the test sections was consistent between the RetroTek-MU, and the portable retroreflectometer with an R2 value of 0.9878. The mobile and portable data closely matched each other with almost no bias as the line of equality and data trend line were nearly on top of each other. The average error was less than 7 percent for any subset of color or marking pattern. The difference between the measurements with and without the RRPMS was less than 3 percent different on average.

The testing and results described in this report provide quantitative information as to the accuracy of data collected with the RetroTek-MU mobile pavement marking retroreflectometer across a range of factors.

Download the full report here