In 2004, the Florida Department of Transportation (FDOT) acquired a Mobile Retroreflectometer Unit (MRU) to safely collect and process pavement marking retroreflectivity for a Pavement Marking Management System (PMMS). The goal of the program is the transition from site specific handheld retroreflectometers and subjective visual surveys to a continuous and high speeddata collection methodology. MRU technology is still relatively new and previous studies have shown it is critical to understand the operations of the device for valid test results. Crucial to the valid results is the calibration step, which is used to standardize the MRU response to a known retroreflectivity sample. Current calibration procedures typically require use of a short section of pavement line marking, often referred to as a beaded stripe, with a known retroreflectivity value as the MRU calibration standard. The beaded stripe has the advantage of being similar to the typical material measured by the MRU, but is inherently non-uniform due to a non-homogeneous pattern of glass bead placement and size. The non-uniformity of the glass beads creates the potential for issues with accuracy and repeatability of the calibration step. Ceramic blocks, which are used as the calibration standard for handheld retroreflectometers, have demonstrated a spatially uniform retroreflectivity response. This paper compares MRU calibration with the beaded stripe to that of a ceramic block, in part to showan alternative calibration standard. Initial testing has shown comparablecalibration results when using a ceramic block versus the beaded line stripe. The study also attempts to validate the laboratory test results by conducting field experiments, comparing both the beaded calibration stripe and the ceramic block calibration methodologies.
Abstract