One Way Sign
MUTCD R6-1
Traffic flows only in the direction of the arrow.
What it looks like
A horizontal black rectangle with the words ONE WAY in white capitals and a white arrow showing the single direction of travel.
When you'll see it
Posted at intersections and along one-way streets, especially in downtown grids and where divided roadways separate opposing traffic.
What to do
You must travel only in the direction the arrow points; do not turn or drive against the marked flow.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.