Laboratory-Accelerated Versus Outdoor Weathering for Retroreflective Sheeting Specifications

Abstract

Laboratory-accelerated weathering tests are used instead of outdoor weathering tests in specifications for products intended for long-term outdoor use because they provide fast results. These accelerated tests are used as a measure of acceptable weathering performance for a material. Acceptance of results from laboratory-accelerated tests in product specifications is based on two major assumptions: (a) materials that pass the requirements of the laboratory-accelerated test meet outdoor durability requirements, and (b) results from laboratory-accelerated tests are much more consistent than those from outdoor exposures. Numerous examples illustrate the errors that occur when these assumptions are wrong. Material with good outdoor durability can fail to meet the requirements of a specified laboratory-accelerated test, or material with poor outdoor durability will pass the requirements of the specified laboratory-accelerated test. Between-lab variability can cause a product to be rejected by a specifier although the same test run by the supplier produced acceptable results. For retroreflective sheeting, outdoor exposures are actually more consistent than the laboratory-accelerated exposure most commonly used in specifications. To assure minimum acceptable durability, 36-mo outdoor exposures are recommended for most retroreflective sheeting specifications. However, results from these exposure tests do not predict the ultimate service life of retroreflective sheetings.

A Control Sign Facility Design to Meet the New FHWA Minimum Sign Retroreflectivity Standards

“…Laboratory tests have been found to be highly variable, unreliable in predicting sign durability, and relatively expensive when compared with outdoor exposure tests (Ketola, 1999).…”

“…The NTPEP program data are not helpful in predicting sign service life (when signs are expected to deteriorate to levels below the FHWA minimum; Ketola, 1999). There is no current source for long-term controlled sign performance data.…”

“…Sign deterioration has been studied under controlled (where signs are separate and away from traffic) and uncontrolled outdoor conditions, as well as in indoor laboratory tests. Laboratory tests have been found to be highly variable, unreliable in predicting sign durability, and relatively expensive when compared with outdoor exposure tests (Ketola, 1999).…”

“…Generally, R 2 values for ordinary least squares deterioration curves (of retroreflectivity vs. time) generated from the NTPEP data are greater than .8; however, the sample size is small as there are only two weathered samples per sheeting type. The NTPEP program data are not helpful in predicting sign service life (when signs are expected to deteriorate to levels below the FHWA minimum; Ketola, 1999). There is no current source for long-term controlled sign performance data.…”

A Control Sign Facility Design to Meet the New FHWA Minimum Sign Retroreflectivity Standards

“…Laboratory tests have been found to be highly variable, unreliable in predicting sign durability, and relatively expensive when compared with outdoor exposure tests (Ketola, 1999).…”

“…The NTPEP program data are not helpful in predicting sign service life (when signs are expected to deteriorate to levels below the FHWA minimum; Ketola, 1999). There is no current source for long-term controlled sign performance data.…”

“…Sign deterioration has been studied under controlled (where signs are separate and away from traffic) and uncontrolled outdoor conditions, as well as in indoor laboratory tests. Laboratory tests have been found to be highly variable, unreliable in predicting sign durability, and relatively expensive when compared with outdoor exposure tests (Ketola, 1999).…”

“…Generally, R 2 values for ordinary least squares deterioration curves (of retroreflectivity vs. time) generated from the NTPEP data are greater than .8; however, the sample size is small as there are only two weathered samples per sheeting type. The NTPEP program data are not helpful in predicting sign service life (when signs are expected to deteriorate to levels below the FHWA minimum; Ketola, 1999). There is no current source for long-term controlled sign performance data.…”

A Control Sign Facility Design to Meet the New FHWA Minimum Sign Retroreflectivity Standards

“…Laboratory tests have been found to be highly variable, unreliable in predicting sign durability, and relatively expensive when compared with outdoor exposure tests (Ketola, 1999).…”

“…The NTPEP program data are not helpful in predicting sign service life (when signs are expected to deteriorate to levels below the FHWA minimum; Ketola, 1999). There is no current source for long-term controlled sign performance data.…”

“…Sign deterioration has been studied under controlled (where signs are separate and away from traffic) and uncontrolled outdoor conditions, as well as in indoor laboratory tests. Laboratory tests have been found to be highly variable, unreliable in predicting sign durability, and relatively expensive when compared with outdoor exposure tests (Ketola, 1999).…”

“…Generally, R 2 values for ordinary least squares deterioration curves (of retroreflectivity vs. time) generated from the NTPEP data are greater than .8; however, the sample size is small as there are only two weathered samples per sheeting type. The NTPEP program data are not helpful in predicting sign service life (when signs are expected to deteriorate to levels below the FHWA minimum; Ketola, 1999). There is no current source for long-term controlled sign performance data.…”

A Control Sign Facility Design to Meet the New FHWA Minimum Sign Retroreflectivity Standards

“…Laboratory tests have been found to be highly variable, unreliable in predicting sign durability, and relatively expensive when compared with outdoor exposure tests (Ketola, 1999).…”

“…The NTPEP program data are not helpful in predicting sign service life (when signs are expected to deteriorate to levels below the FHWA minimum; Ketola, 1999). There is no current source for long-term controlled sign performance data.…”

“…Sign deterioration has been studied under controlled (where signs are separate and away from traffic) and uncontrolled outdoor conditions, as well as in indoor laboratory tests. Laboratory tests have been found to be highly variable, unreliable in predicting sign durability, and relatively expensive when compared with outdoor exposure tests (Ketola, 1999).…”

“…Generally, R 2 values for ordinary least squares deterioration curves (of retroreflectivity vs. time) generated from the NTPEP data are greater than .8; however, the sample size is small as there are only two weathered samples per sheeting type. The NTPEP program data are not helpful in predicting sign service life (when signs are expected to deteriorate to levels below the FHWA minimum; Ketola, 1999). There is no current source for long-term controlled sign performance data.…”