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 and its companion volume the Standard Highway Signs. 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. Similarly to general traffic codes in the Unites States, 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.
Regulatory
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 found only 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.
R1 Series: Stop and Yield
The MUTCD's R1 series is for stop and yield. As not all situations are covered, several states have their own standards in addition to the MUTCD. The 4-WAY and 3-WAY plaques were deprecated in the 2009 Edition of the MUTCD in favor of the ALL WAY plaque.
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 always 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 due to MUTCD restrictions, increasing the rarity of such signs.
R3 Series: Lane Usage and Turns
The MUTCD's R3 series of signs is for lane usage and turn signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R4 Series: Regulation of Movement
The MUTCD's R4 series of signs is for the regulation of movement signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R5 Series: Exclusionary
The MUTCD's R5 series of signs is for exclusionary signs. As all situations are not covered, several states have their own standards in addition to the MUTCD. The most common of these signs is the do not enter sign.
The MUTCD's R6 series of signs is for one way and divided highway signs. As all situations are not covered, several states have their own standards in addition to the MUTCD. The most common of these signs is the one way sign.
R7 Series: Parking
The MUTCD allows for three types of parking signs, permissive, no parking, and no standing. However, in most states, there is an additional more restrictive one, no stopping. These signs are found in the R7 series of signs in the MUTCD. As all situations are not covered, several states and local governments have their own standards in addition to the MUTCD.
Permissive Parking
These types of signs allow for parking for either an unlimited or varied amount of time. These types are often used in conjunction with parking meters and parking permits. These signs are specified by the MUTCD to be green on white. Local variations do occur with additional information and slightly different designs.
No Parking
No parking signs indicate that loading or unloading there while temporarily stopped is permitted, but parking is not. Some no parking signs display time restrictions, while others are permanent restrictions. There are also temporary versions of the signs, often of similar design to the permanent ones. These signs are specified by the MUTCD to be red on white, although local variations do occur.
No Standing
No standing signs indicate that stopping temporarily to load or unload passengers is allowed, while parking is not allowed. As with no parking signs, some restrictions displayed on the signs are permanent and some are time based. The signs are also specified by the MUTCD to be red on white, but local variations exist.
No Stopping
No stopping signs indicate that stopping is only allowed in order to obey a traffic sign, signal, traffic agent, police officer, or to avoid conflicts with other vehicles. These are the most restrictive of the parking signs. They are typically red on white.
R8 Series: Parking and Emergency Restrictions
The MUTCD's R8 series of signs is for parking restriction and emergency restriction signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R9 Series: Bicycles and Pedestrians
The MUTCD's R9 series of signs is for bicycle and pedestrian signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R10 Series: Traffic Signal
The MUTCD's R10 series of signs is for traffic signal related signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R11 Series: Road Closed
The MUTCD's R11 series of signs is for road closure related signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R12 Series: Weight Limits
The MUTCD's R12 series of signs is for weight limit related signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R13 Series: Weigh Stations
The MUTCD's R13 series of signs is for weigh station related signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R14 Series: Truck Routes
The MUTCD's R14 series of signs is for Truck route related signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
The MUTCD's R15 series of signs is for rail and light rail related signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
R16 Series: Seat Belts and Headlight Use
The MUTCD's R16 series of signs is for seat belt and headlight use related signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
Other Local and State Series
The MUTCD does not cover all situations, so states and local governments have developed their own regulatory signs. In these, the sign categories are assigned series either using the MUTCD style, but higher than 16, or use a unique series nomenclature system.
Schools
The S series of signs is specially designated by the MUTCD for use around schools. Some states have additional school warning related signs in the S series, as well as in the W series of warning signs and/or the R series of regulatory signs of the state supplement or state MUTCD. The MUTCD as of 2009 requires school warning signs to have fluorescent yellow-green background color.
Warning
Warning signs are found in the W series of the national MUTCD. They highlight existing conditions, such as a curve, school, dead end street, or traffic signal. They can also warn possible danger such as bumps, bicycles, low flying aircraft, or emergency vehicles. These signs are either yellow or fluorescent yellow in color and, with the exception of a few signs, are usually diamond shaped and sometimes have square or rectangular smaller signs or plaques associated with them. Most W series signs can also be found with orange backgrounds for temporary use in situations such as construction zones. Some of the temporary use signs are only for use in temporary situations.
W1/2 Series: Turns, Curves, Intersections
The MUTCD's W1/2 series of signs is for warning signs relating to curves, turns and intersections. As not all situations are covered, several states have their own standards in addition to the MUTCD.
W3 Series: Advance Traffic Control
The MUTCD's W3 series of signs is for warning signs relating to advance traffic controls such as speed limits and signals. As all situations are not covered, several states have their own standards in addition to the MUTCD. The MUTCD provides options for graphic and text signs.
W4 Series: Lanes and Merges
The MUTCD's W4 series of signs is for warning signs relating to lane merges and added lanes, as well as lane endings. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W5 Series: Road Width Restrictions
The MUTCD's W5 series of signs is for warning signs relating to road width restrictions. As all situations are not covered, several states have their own standards in addition to the MUTCD. The MUTCD provides options for graphic and text signs.
W6/7 Series: Divided Highways and Hills
The MUTCD's W6/7 series of signs is for warning signs relating to divided highways, hills, and grades. As all situations are not covered, several states have their own standards in addition to the MUTCD. The MUTCD provides options for graphic and text signs.
W8 Series: Pavement and Roadway Conditions
The MUTCD's W8 series of signs is for warning signs relating to pavement and roadway conditions. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W9/10 Series: Lane Transitions and Railroad Crossings
The MUTCD's W9/10 series of signs is for warning signs relating to lane transitions and railroad crossings. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W11 Series: Advance Warnings and Crossings
The MUTCD's W11 series of signs is for warning signs relating to advance warnings and crossings. As all situations are not covered, several states have their own standards in addition to the MUTCD. The MUTCD allows use of a fluorescent yellow-green background color for signs relating to people crossing the road.
Emergency Vehicles
The MUTCD only provides for a warning of fire stations in the W11 series. Most states have their own signs for other emergency vehicle types which may enter the road.
Children
The MUTCD specifies no children related signs in the W11 series. Several states, counties, and municipalities have signs for situations as children at play as well as children with various medical conditions. Some of these signs vary from state to state as there is no federal standard.
Bicycles
The MUTCD provides several signs in the W11 series warning of bicycles and for signing bicycle facilities. Several states and localities have their own specific bicycle related signs as well.
Vehicles
The MUTCD provides several signs in the W11 series dealing with vehicles. Several states have additional signs for other types of vehicles and situations regarding vehicles not covered by the MUTCD.
Pedestrians, Transit, and Aviation
The MUTCD provides several signs in the W11 series dealing with pedestrians, transit, and aviation. Several states have additional signs for other types of vehicles and situations regarding vehicles not covered by the MUTCD.
Animals
The MUTCD provides several signs in the W11 series dealing with animals. Several states have additional signs for other types of animals not covered by the MUTCD.
Driveways and Entrances
The MUTCD does not provide signs in the W11 series dealing with driveways and entrances. Many states have their own sign standards dealing with these situations that they place in their own W11 series.
W12 Series: Low Clearances
The MUTCD's W12 series of signs is for warning signs relating to low clearances. As all situations are not covered, several states have their own standards in addition to the MUTCD. Metric low clearance signs in meters 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 due to system restrictions, increasing the rarity of such signs.
W13 Series: Advisory Speeds
The MUTCD's W13 series of signs is for warning signs relating to advisory speeds. As all situations are not covered, several states have their own standards in addition to the MUTCD. Speed limits in the United States are always in miles per hour. Metric advisory speed 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 due to system restrictions, increasing the rarity of such signs.
W14 Series: Dead End Streets and No Passing Zones
The MUTCD's W14 series of signs is for warning signs relating to dead end streets and no passing zones. As all situations are not covered, several states and local governments have additional signs for other types of situations not covered by the MUTCD.
W15 Series: Playgrounds
The MUTCD's W15 series of signs is for warning signs relating to playgrounds. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W16 Series: Supplemental Plaques
The MUTCD's W16 series of signs is for supplemental plaques for warning signs. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W17 Series: Speed Humps
The MUTCD's W17 series of signs is for warning signs relating to speed humps. As all situations are not covered, several states have their own standards in addition to the MUTCD.
The MUTCD's W19 series of signs is for warning signs relating to the end of a controlled access highway. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W20 Series: Work Zones
The MUTCD's W20 series of signs is for warning signs relating to work zones. These signs are typically orange background ones used for temporary situations. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W20 Series: Road Ends
The MUTCD Road Closed signs alert drivers that the road is closed; these signs are white.
W21 Series: Road Work
The MUTCD's W21 series of signs is for warning signs relating to road work. These signs are typically orange background ones used for temporary situations. As all situations are not covered, several states have their own standards in addition to the MUTCD
W22 Series: Blasting Zones
The MUTCD's W22 series of signs is for warning signs relating to blasting zones. These signs are typically orange background ones used for temporary situations. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W23 Series: Slow Traffic
The MUTCD's W23 series of signs is for warning signs relating to slow traffic. These signs are typically orange background ones used for temporary situations. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W24 Series: Lane Shifts
The MUTCD's W24 series of signs is for warning signs relating to lane shifts, where traffic would be diverted slightly toward the left or right of the roadway, but the route is otherwise unchanged. These signs are typically orange background ones used for temporary situations. As all situations are not covered, several states have their own standards in addition to the MUTCD.
W25 Series: Oncoming Traffic Has Extended Green
The MUTCD's W25 series of signs is for warning signs oncoming traffic having an extended green signal at a traffic light. As all situations are not covered, several states have their own standards in addition to the MUTCD.
Miscellaneous
The MUTCD does not provide signs dealing with some other road and highway situations. Many states have their own sign standards dealing with these situations.
Guide
Guide signs include highway route markers, which are reassurance markers, interchange signs, including advance guide and exit signs, and mile markers. Advance guide and exit signs usually feature control cities or other locations to help direct drivers toward their desired destination. The position of the exit number plaque indicates right or left exit.
Interchange signs
Shield markers
Note: State markers are illustrative examples; all states may select their own marker shapes or use the default circle. See Numbered highways in the United States#State highways and other similar systems.
