Road signs in the United States
In the United States, road signs are, for the most part, standardized by federal regulations, most notably in the Manual on Uniform Traffic Control Devices (MUTCD) and its companion volume the Standard Highway Signs (SHS). There are no plans for adopting the Vienna Convention on Road Signs and Signals standards.
Twenty-three states along with the District of Columbia and Puerto Rico use the manual without any alterations, 20 states have adopted it in conjunction with a supplemental volume, and seven states have a state version in substantial conformance to the MUTCD. There are also localized versions that are used in large cities such as New York City which use a naming system compatible with the MUTCD and/or state supplement. The MUTCD and SHS establish seven general categories of signs for road and highway use (all signs from national MUTCD, unless noted).
Regulatory signs give instructions to motorists, pedestrians, and cyclists. Signs such as stop, no parking, no turns, and yield are considered regulatory signs. Some have special shapes, such as the octagon for the stop sign and the X shape for railroad crossings. Some signs can be localized, such as no parking, and some are only found in state and local jurisdictions as they are based on state or local laws, such as New York City's "Don't Block the Box" signs. These signs are in the R series of signs in the MUTCD and typically in the R series in most state supplements or state MUTCDs.
The MUTCD's R1 series of is for stop and yield. As not all situations are covered, several states have their own standards in addition to the MUTCD.
Yield (Give Way)
All way plate
Yield to pedestrians,
New York City
State law Yield to pedestrians in crosswalk
State law stop for pedestrians in crosswalk
4-way plate
The MUTCD's R2 series is for speed limit signs. Some state supplements and state MUTCDs place various speed limit signs in other series. As all situations are not covered, several states have their own standards in addition to the MUTCD. Speed limits in the United States are in miles per hour. Metric speed limit signs in kilometers per hour are authorized but extremely rare, usually seen near the borders with Canada and Mexico, both of which use the metric system. Many states however disallow the use of metric signs on state-maintained roads, increasing the rarity of such signs.
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