Reductions in Traffic Sign Retroreflectivity Caused by Frost and Dew

Abstract

A study of in-service traffic signs was undertaken to quantify the average effects of frost and dew on their retroreflective capabilities. The results were then compared with proposed minimum retroreflectivity standards recently developed by FHWA-sponsored research for inclusion in the Manual on Uniform Traffic Control Devices. Although the effects of frost and dew were found to be variable, average reductions in retroreflectivity levels of 79% and 60%, respectively, were found. None of the different colored signs sampled with Type I (engineering grade) sheeting was found to meet the proposed minimum levels when covered in frost or dew (with the exception of signs with white backgrounds covered in dew), even though all signs were in like-new condition. Signs sampled with Type III (high intensity) sheeting had mixed results. The findings are significant enough that they should be considered in the development of the final version of the FHWA national standards. Furthermore, those jurisdictions subject to frequent cycles of frost and dew should review usage guidelines governing the grade of sign materials used, allowing for expected loss of retroreflectivity.

An Analysis of the Factors Influencing the Retroreflectivity Performance of In-Service Road Traffic Signs

“…The best regression models using only the factors that can be collected without instruments were the logarithmic regression models in Equations ( 4) and (5), as shown in Table 7:…”

“…These predictors can be easily collected without the need for expensive measuring instruments. Three predictors can be used in Equation (5) to predict retroreflectivity: the class of the retroreflective sheeting, the color of the sign, and the age of the sign.…”

“…At night, road traffic signs reflect the light coming from vehicles to the road users so that they can see these signs [4,5]. The property of returning the light to the source (vehicle, in this case) is called retroreflectivity [6].…”

Predicting Traffic Sign Retro-Reflectivity Degradation Using Deep Neural Networks

“…Furthermore, the study considered only two sheeting colors (white and green), which reduces its applicability to other regions having different sign sheeting types and colors. Another study investigated the influence of frost and dew on traffic sign retro-reflectivity and noted an average decrease of 79% and 60%, respectively, in the retro-reflectivity values [18]. Engineering grade (Type-I) sheeting was observed to be severely affected as compared to high intensity (Type-III) sheeting.…”

Legibility of Urban Highway Traffic Signs Using New Retroreflective Materials

“…Generally, these studies have corroborated the promise of several newer reflective materials (e.g., types VII, VIII and IX) to provide superior performance to more commonly used materials (e.g., types I and III) in terms of higher luminances or longer legibility distances (Bible and Johnson 2002;Carlson and Hawkins 2003;Zwahlen et al 2003;Carlson and Holick 2005). However, the relationship between a material type and its luminance is dependent on a variety of factors such as the light source used to illuminate the material, the geometry, the location and angular displacement of the sign, age and cleanliness of the sign, the presence of ambient illumination, complexity of the surrounding environment, weather and many other factors that are almost always beyond the control of highway engineers (Goodspeed and Rea 1999;Nuber and Bullock 2002;Hildebrand 2003;Carlson and Urbanik 2004). According to one more scientist, no reliable differences between encapsulated lens and microprismatic material types were found (Garvey et al 1997).…”