Why did old stop signs “bleach” and fade in the sun, and how did they solve this problem in more recent times to prevent this?
Old ones used paint. New ones use 3M reflective sheeting specially designed to not fade in sunlight.
Some really, *really *old ones may not have been red to begin with, but yellow!
The reflective sheeting is much better than paint (and there are different qualities of sheeting) but problem remains that this sheeting does wear out. The Manual of Uniform Traffic Control Devices (MUTCD) is the standard for road signs, and minimum sign retroreflectivity is defined as part of that standard. Agencies that have road signs need to have a maintenance plan such as measuring the retroreflectivity periodically or simply replacing the signs after they have been in service for so many years. There are advantages and disadvantages to such plans so how it is done will vary from place to place.