Center for High Accuracy Retroreflection Measurements (CHARM)

In 1993, the United States Congress 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." The establishment of a national standard for minimum levels of retroreflectivity requires methods to accurately measure retroreflectivity. CIE has established procedural standards for measuring retroreflective traffic control devices. These standards ensure that the procedures used to measure retroreflectivity are consistent. They do not ensure that the instruments used are accurate. A need exists for calibration standards of retroreflectivity to establish a traceable method for determining the accuracy of measurements. Calibrated standards will significantly reduce the prospect of either incorrectly failing or passing materials. The adverse impact of the former is economic, while the later is on safety.

NIST was awarded a contract by the National Cooperative Highway Research Program (NCHRP Project 05-16) to develop a dedicated reference instrument for measuring retroreflective materials, and a calibration program that provides traceability to the relevant national scales maintained by NIST.

Retroreflection is reflection in which the reflected rays are preferentially returned in directions close to the opposite of the direction of the incident rays, this property being maintained over wide variations in the direction of the incident rays. The NIST CHARM facility is composed of three key elements: a projection source, a large frame high accuracy goniometer for positioning the sample, and a three axis detection system.

Calibration Service:

NIST provides calibration service for submitted retroreflective materials under NIST Test No. 37100 Special Photometric Tests. NIST can calibrate signage materials and pavement marking materials, for coefficient of luminous intensity, coefficient of retroreflection, and coefficient of retroreflective luminance. Please contact c.miller [at] nist.gov (Cameron Miller) to discuss details of test artifacts and obtain quotation for the requested calibration.

Selected Publication:

• National calibration facility for retroreflective traffic control materials, NCHRP Web-only Document 72 (Project 05-16)