What are the requirements for the use of roll up speed limit signs used in work zones?
The work zone speed limit can be set by the agency with jurisdiction based upon the normal speed limit of that section of highway. The normal speed limit is discussed in the Quick Answer "Who set speed limits on local highways?" as well as the 2011 Traffic Sign Handbook (starting on Page 91).
The speed limit in the work zone cannot be lowered by more than 20 mph and must be at least 25 mph.
The bottom of any roll up signs used in a work zone need to be at least 1 foot above the ground and only used with active work zones. They should not be left up when the work is not active otherwise they will lose effectiveness very quickly.
Chapter 6 of the MUTCD, specifically the section on signs (6F)
V&T law section 1180(f): - Click on Laws then select Vehicle and Traffic