Development of Specifications for Reflex-Reflective Materials

Evolutionary changes in highway design, automobiles and retro-reflective products prompted Kentucky to undertake a study to update specification requirements for signing materials, delineators and coating compounds. The study was primarily concerned with geometric relationships between the driver, headlamps and traffic signs; investigation of reflectivity, color, durability and other properties of available reflective materials; adoption of testing apparatus to measure material properties; and development of test procedures. A review of specific sign viewing conditions on the road indicated the appropriateness of reflectivity testing at 0.5-degrees and 0.2-degrees angles of divergence. These angles, however, limit examination of materials at viewing distances in excess of 300 feet to the sign. Selection of a maximum angle of incidence of 30 degrees was found to be more than adequate to insure the performance even in the most extreme situations of sign viewing. An ESNA reflex-photometer was found to be an acceptable tool for reflectivity testing. The adoption of the device, however, required substitution of associated instrumentation and development of testing procedures. The photometric measurements were correlated with conventional tunnel photometers. The data on some color materials compared favorably and on others differed significantly, but the data could be corrected to yield comparable values. Color requirements for commonly used sign sheeting materials were defined in terms at CIE chromaticity coordinate limits. A colorimeter was acquired to serve as a quality control tool for specific materials. To enhance nighttime reflectance of highway signs under wet conditions, sign materials were required to exhibit smooth, flat surfaces. A glossmeter was adopted for testing surface sheen of materials to insure the desired texture. Accelerated weathering tests were conducted on various brand-name retro-reflective materials. An 800-hour weatherometer test was judged to be sufficient for durability testing of sign sheeting and coating compounds and that they should retain 80% of minimum specified reflectivity. A revised specification for reflex-reflective materials was prepared. The document was deliberately designed as a general specification and includes only those features which were judged most essential from the standpoint of material identification, classification and insuring adequate in-service performance of materials used in highway signs, reflectors used in traffic delineators, and coating compounds applied to structures for safety purposes