What are the criteria for the placement of a “Dangerous Curve” or “Dangerous Turn” sign?
This is going on the “better safe than sorry” idea, but I would say that they are pretty liberal about it. I mean, if it’s even remotely dangerous, they probably slap one of those signs up. Better safe than sorry.
This article in Road Management & Engineering Journal describes an instrument called a ball-bank indicator used to determine the safe speed for a curve. Another article from the same publication describes a study conducted to determine peoples’ behavior in driving through curves.
The DOT has a site for the Manual on Uniform Traffic Control Devices that might offer up some more info. I get the impression that state governments can make up their own criteria.
And to follow up on Zinger’s response, if you peruse the Road Management & Engineering Journal you’ll note that manny lawsuits are filed alleging that accidents were caused by failure to erect warning signs.