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Some countries, like Germany, show text on one-way signs

A Swedish one-way sign used on T junctions

"No entry" signs are often placed at the exit ends of one-way streets

A one-way street is a street on which vehicles can only move in one direction. On this type of street a sign is posted showing which direction the vehicles can move in: commonly an upward arrow, or on a T junction where the main road is one-way, an arrow to the left or right. At the end of the street through which vehicles may not enter, a prohibitory traffic sign "Do Not Enter" or "No Entry" sign is posted, e.g. with that text, or a round red sign with a white horizontal bar. Sometimes one portion of a street is one-way. another portion two-way. An advantage of one-way streets is that drivers do not have to watch for cars coming in the opposite direction on this type of street.

One-way streets may also be part of a one-way system, which facilitates a smoother flow of traffic through, for example, a city centre grid. This is achieved by arranging one-way streets that cross in such a fashion as to eliminate right turns (for driving on left) or left turns (for driving on right). Traffic light systems at such junctions may be simpler, and may be coordinated to produce a green wave.

The first one-way street was established in Lima. The first one-way street in London was Albemarle Street in Mayfair, the location of the Royal Institution. It was designated London's first one-way street because the public science lectures there were so popular [1]. The first one-way streets in Paris were the Rue de Mogador and the Rue de la Chaussée-d'Antin, created on 13 December 1909.

• Street is too narrow for movement in both directions-in this case parking will only be allowed on one side of the street or not at all.
• To prevent drivers from cutting through residential streets rat runs to bypass traffic lights or other requirements to stop.
• Part of a one-way pair of two parallel one-way streets in opposite directions.
• For a proper functioning of a system of paid parking or other paid access.
• To keep traffic low, especially if the street is historic.
• To reduce pollution from automobiles.

Sometimes there is one-way walking for people, for smooth traffic flow, or in the case of entrance checks (such as ticket checks) and exit checks (e.g. the check-out in a shop). They may be outdoors, e.g. an extra exit of a zoo, or in a building, or in a vehicle, e.g. a tram.

In addition to just signs, there may be various forms and levels of enforcement, such as:

• personnel
• a turnstile; turnstile jumping is possible
• a High Entrance/Exit Turnstile (HEET)
• a door or gate that can only be opened from one side (a manual or electric lock, or simply a door that is pushed open and has no doorknob on the other side), or automatically opens from one side; with help from someone on the other side, it can usually conveniently be passed in the "wrong" direction. Examples:
  • entrance of a shop
  • an emergency exit; it may activate an alarm, useful both for proper and improper use of the door
• an escalator; the escalator can be passed in opposite direction, climbing up or down the stairs faster than it moves
• a one-way revolving door

Sometimes a "soft" traffic control system is supported by personnel keeping an eye on things.

Sometimes a door or gate can be opened freely from one side, and only with a key or by inserting a coin from the other side (house door, door with a coin slot, e.g. giving entrance to a pay toilet). The latter can be passed without paying when somebody else leaves, and by multiple persons if only one pays (as opposed to a coin-operated turnstile).

v • d • e Traffic Signs
Signs	Warning sign • Regulatory sign • Priority to the right • Yield sign • Stop sign • Prohibitory traffic sign • One-way traffic • Speed limit • Advisory speed limit • Mandatory sign • Special regulation sign • Informative sign • Information, facilities, or service sign • Direction, position, or indication sign • Additional panels
By country	Iceland • Ireland • Malaysia • Norway • Singapore • Sweden • United Kingdom (Scotland)
Lights	Traffic light • Variable-message sign
Typefaces	Clearview • DIN 1451 • FHWA Series • Frutiger • NPS Rawlinson Roadway • Transport • Tratex
Conventions	Vienna Convention on Road Traffic • Vienna Convention on Road Signs and Signals • Manual on Uniform Traffic Control Devices