What does a 'One Way' sign indicate, and how must a driver respond?

A 'One Way' sign (a regulatory sign, often a black-and-white rectangle with an arrow) indicates that traffic on that street moves in only one direction — the direction the arrow points. Drivers must travel only in that direction and must not enter against the flow. One-way streets are common in cities to improve traffic flow. A related sign, 'Do Not Enter' (a red circle with a white horizontal bar), marks where you must not enter, such as the wrong end of a one-way street or an exit ramp. Obeying one-way and do-not-enter signs prevents dangerous wrong-way driving and is essential regulatory-sign knowledge.