For those who haven't heard of this, it stands for the "Manual on Uniform Traffic Control Devices" (MUTCD). The official site can be found here:

http://mutcd.fhwa.dot.gov/

It is the "department of transportation" rules that states must comply with in regards to traffic lights, speed limits, etc.

I have read that places like the National Motorists Organization

http://www.motorists.org/

use it in court to show that the states are not in complaince with said road, sign or speed limit. But I have seen it literally ignored when challenged in court. (Surprise, surprise). Does anyone have any more data on this?