New Facility for Calibrating Retroreflectometers

This digest announces the results of NCHRP Project 05-16, which established a facility for the calibration of portable retroreflectometers. The facility is operated by the National Institute of Standards and Technology. Retroreflective traffic control devices are widely used for nighttime visibility and safety. Congress has directed the U.S. Department of Transportation to establish "a standard for a minimum level of retroreflectivity that must be maintained for pavement markings and signs which apply to all roads open to public travel." Establishing a national standard for minimum levels of retroreflectivity requires accurate methods to measure retroreflectivity. Instruments are commercially available for measuring the retroreflectivity of signs and markings, and documented standards establish procedures for such measurements. However, there can be significant variability among instruments measuring the same object, and the standards do not ensure accuracy of the instruments. Prior to undertaking this research, there were no traceable methods in the United States to determine the accuracy of measurements, because national calibration standards for retroreflectivity did not exist. NCHRP Project 05-16 developed dedicated reference instrumentation to provide national calibration standards for retroreflectivity, thereby improving the accuracy of measurements made by other instruments.