Standard Practice for Evaluating Nighttime Retroreflective Sheeting Effectiveness Using Positive-Contrast Textual Sign Scenario Performance Analysis

Importancia y uso:

5.1 Retroreflective sheeting is commonly used to improve the nighttime visibility and legibility of traffic signs under vehicle headlight illumination. This standard provides a procedure for evaluating the nighttime retroreflective performance of sign sheeting used in roadway signing in terms of an overall average performance index for predefined road scenarios.

5.2 A procedure to characterize the relationship between sign luminance supply and driver luminance demand at night without conducting field work helps traffic engineers and transportation agencies responsible for specifying highway construction materials and maintaining roadway safety in making informed decisions about the performance of retroreflective sheeting on the signs. The procedure requires the comprehensive measurement of the retroreflective properties of a sheeting according to Practice E809 over a wide range of angles.

5.3 A variety of retroreflective sheeting is available for use on traffic signs. Coefficients of retroreflection are typically measured for a standard set of angle combinations and are used, in part, to certify conformance to a specification or standard. However, while coefficients of retroreflection on some standard angle sets can provide a general idea about a sheeting’s retroreflectivity and help certify conformance to a standard, a more comprehensive analysis is needed to determine how well a sheeting is expected to serve drivers in general, or in specific use-cases. Drivers of different vehicles viewing a multitude of signs in the real world experience a much more complex set of angular combinations than those captured in the standard angle sets. Furthermore, drivers observe luminance, which is affected by not only the coefficient of retroreflection, but also by headlight illumination, distance from the vehicle to the sign, and light attenuation, among other factors.

5.4 This practice utilizes a set of driver sign viewing scenarios. When combined with the coefficients of retroreflection at the corresponding geometry, the luminance as observed by the driver is calculated. The luminance requirements of the driver for varying percentiles are also tabulated for the user. Comparing the luminance supply from the sign with the luminance demand of drivers provides an assessment of the expected “performance index” in each scenario.

5.5 The data on the luminance needs of the driver represents the visual performance of a subset of legal drivers in the United States of 55 years of age or older and may not represent the visual performance of the entire driver demographics.

Subcomité:

D04.38

Volúmen:

04.03

Número ICS:

01.080.10 (Public information symbols. Signs. Plates. Labels)