The National Academies

NCHRP 05-16 [Completed]

National Calibration Standards for Measuring Retroreflectivity

  Project Data
Funds: $535,000
Research Agency: National Institute of Standards and Technology
Principal Investigator: Cameron Miller
Effective Date: 12/12/2001
Completion Date: 12/30/2004

Background: 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 will require 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. There are currently no traceable methods in the United States to determine the accuracy of measurements, because national calibration standards for retroreflectivity do not exist.

This research is intended to develop dedicated reference instrumentation to provide national calibration standards for retroreflectivity, thereby improving the accuracy of measurements made by other instruments. The instrumentation shall have the widest possible dynamic range to measure current and anticipated levels of performance of retroreflective traffic control materials. The reference instrumentation will use modern techniques to perform calibrations in compliance with all relevant standards. This instrumentation will have sufficient flexibility to measure spectral and luminous quantities of retroreflective traffic control materials over the full range of angles and will have the best possible accuracy.

Objective: The objective of this project is to develop dedicated reference instrumentation suitable for calibration and characterization of retroreflective reference materials.

Tasks: To accomplish the objective the following tasks are envisioned: Phase I: (1) Conduct a literature review. The literature review shall include, at a minimum, existing national and international calibration and measurement methods of, and specifications for, retroreflective traffic control materials. In reviewing these measurement methods and specifications, the following, at a minimum, shall be considered: photometric, geometric, and colorimetric properties. (2) Develop and describe the process required to obtain retroreflective values based upon traceable fundamental quantities. Estimate the levels of accuracy obtainable over the dynamic ranges represented in typical retroreflective traffic control materials (e.g., sheeting materials, pavement marking materials and pavement markers). (3) Develop measurement protocols to fulfill the requirements for characterization of retroreflective traffic control materials. These characterizations shall include, at a minimum, the measurement of (a) various sizes of retroreflective traffic control materials in conformance with applicable standards; (b) all angles needed to fully describe retroreflective traffic control materials, including observation angles up to at least 2.5 degrees; and (c) spectral characteristics of retroreflective traffic control materials in conformance with applicable standards. (4) Determine the technical aspects and economic impacts of the inclusion of the measurement and characterization of fluorescent materials. (5) Develop a tentative program to provide standard retroreflective reference materials and recalibration services for those materials. (6) Develop the preliminary design for the instrumentation (including data acquisition protocol) and a plan for validation of the measurement processes and results. (7) Prepare an interim report. The interim report shall document the results of Tasks 1 through 6 and include a detailed work plan for Phase II. The contractor shall not proceed with Phase II without the approval of the NCHRP. (8) Meet with the project panel approximately one month after submittal of the interim report. Phase II: (9) Prepare final design and build the instrumentation. (10) Validate the instrumentation and the measurement processes. (11) Conduct a demonstration of the instrumentation and processes for the project panel. (12) Finalize the program to provide standard retroreflective reference materials and recalibration services for those materials.

Status: This project is completed.

Product Availability: NCHRP Research Results Digest 297 announces the results of this project.

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