Background and current status of the development of updated minimum in-service retroreflectivity levels for traffic signs in the United States are described. A summary of the earlier work, conducted from the late 1980s to the mid-1990s, is provided along with descriptions of the relevant validation work. Related events that occurred in the late 1990s are described, and it is shown how, when combined with the assumptions and limitations of the earlier minimum retroreflectivity research, they resulted in a need for updated minimum retroreflectivity levels. The research related to the updated minimum retroreflectivity levels is summarized. A brief description of a second round of national minimum retroreflectivity workshops is also provided. The most recent set of recommended minimum retroreflectivity levels for traffic signs is presented along with a list of suggested research topics based on the limitations associated with the recommendations.
Abstract