Many of the typical warning signs in the U.S. (yellow background, diamond shape and black lettering) warn drivers of changes in the road. They warn of upcoming curves, intersections, merge and lane transitions, road width changes, hills, road splits and lane transitions. They also warn of upcoming traffic signals, pavement conditions (e.g. slippery when wet), low clearance, dead ends, speed humps, lack of traffic signs, playgrounds and bicycle crossings.
There are warning signs that come in non-diamond shapes. School crossings appear on a pentagon-shaped sign with a yellow background and black pictures. Railroad crossings appear on a yellow circle with black lettering and speed advisory signs appear on square signs with yellow backgrounds and black lettering.
Orange warning signs typically deal with roadwork. Usually a work area speed limit of 25 mph is posted, but if not, you should still reduce your speed if you see these orange warning signs. Diamond-shaped signs with black lettering or drawings indicate work zones or that there’s road work occurring, double reverse curves and blasting zones. Horizontal rectangular signs with orange backgrounds warn of slow traffic.
