Synthesis of Sign Deterioration Rates across the United States

Abstract

In response to minimum retroreflectivity standards, transportation departments are implementing sign asset management strategies, which rely upon knowledge of how retroreflectivity decreases as signs weather and age. To provide this knowledge, the authors field-measured over 1000 inservice signs in scattered North Carolina Department of Transportation (NCDOT) divisions, collecting age and retroreflectivity data for white, yellow, red, and green signs and for ASTM sheeting Types I and III. Data from this study and data from five similar US efforts were analyzed using regression to identify the best available deterioration rate estimates, finding that retroreflectivity minimums are usually reached 8 to 15 years after installation.Initial results indicated that the best-fitting relationships between retroreflectivity and age were generally linear and that these models were significant despite having low R 2 values. Because age did not explain some of the variance, the authors re-evaluated their data including NCDOT divisions as a factor, finding that sign deterioration differed significantly by division, indicating that handling practices, manufacturing differences, and environmental exposure may be key deterioration model factors that merit future study.

Analysis of Three Sign Management Program Case Studies

“…Both NCDOT and SCDOT use a sign service life of 10 years for Type III sheeting, which is considered by the majority of the literature to be a conservative approach (Clevenger et al, 2012; Dumont et al, 2013; Kipp & Fitch, 2009; Preston et al, 2014; Re & Carlson, 2012; Re et al, 2011). Most of the previous studies recommended 15 years or above for Type III sheeting (Clevenger et al, 2012; Dumont et al, 2013; Immaneni et al, 2009; Kipp & Fitch, 2009; Pike & Carlson, 2014).…”

“…The RA is calculated as the ratio of light that strikes the sign and the portion of this light that is reflected back to the source. The unit of measurement is candela per lux per meter square (cd/lx/m 2 ; Re, Miles, & Carlson, 2011), which is defined by Immaneni, Hummer, Rasdorf, Harris, and Yeom (2009) as “the ratio of light a sign reflects to a driver (candela (cd)) to the light that illuminates the sign (lux (lx)), per unit area (square meter (m 2 )).” The RA is often measured by a handheld retroreflectometer even though it is time consuming and exposes inspectors to road hazards. An alternative method is to measure retroreflectivity at night using vehicles equipped with retroreflectometers.…”

“…Many studies were conducted to assess how retroreflectivity deteriorates over the years (Clevenger, Colello, & Quirus, 2012; Evans, Heaslip, Boggs, Hurwitz, & Gardiner, 2012; Immaneni et al, 2009; Kipp & Fitch, 2009; Preston, Atkins, Lebens, & Jensen, 2014; Re et al, 2011, etc.) and, although many of them suggested that sign retroreflectivity deteriorates as signs age, only a few obtained successes in proving the extent of this relationship.…”

“…Most studies that developed deterioration models recommended sign service life to be 15 years and above for ASTM Type III sheeting (Clevenger et al, 2012; Dumont et al, 2013; Immaneni et al, 2009; Kipp & Fitch, 2009; Pike & Carlson, 2014). Pulver et al (2018) was the only study that recommended the adoption (South Carolina Department of Transportation [SCDOT]) of a sign service life (Type III sheeting) that is the same as the 10-year sheeting warranty.…”

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

“…The literature has shown that numerous models exist to approximate degradation rates. The authors have proposed one such model (Immaneni et al, 2009). …”