Minimum Retroreflectivity Levels for Blue and Brown Traffic Signs (FHWA-HRT-08-029)

In 2003, the Federal Highway Administration published research recommendations for minimum maintained retroreflectivity (MR) levels for traffic signs. The recommendations included most sign types but not white-on-blue signs or white-on-brown signs. In addition, the 2003 recommended maintained retroreflectivity levels were based on conditions representing dark rural environments. This report describes the research activities and consequent findings related to the development of recommendations for MR levels for white-on-blue signs and white-on-brown signs. This report also includes an investigation related to MR levels needed for complex visual conditions that include glare from oncoming headlamps and fixed roadway lighting. The research used a summary of the pertinent literature to develop an experimental plan to produce luminance thresholds that could be used with a previously developed analytical model to develop a set of recommendations for MR levels for white-on-blue signs and white-on-brown signs. The results for the white-on-blue signs and the white-on-brown signs were integrated into one table that includes the current set of MR levels. Both legend and symbol signs were consolidated into the same recommendations because of similar requirements for luminance thresholds.