Why are signs with blue or brown backgrounds excluded from these retroreflectivity requirements?
At the time that the changes associated with Revision 2 were being developed, the research for signs with blue or brown backgrounds had not yet been completed. However, a research report (Publication No. FHWA-HRT-08-029) that provides minimum recommended retroreflectivity levels for brown and blue signs was completed in 2007 and will be available soon.
