If you are stopped at an intersection and wish to turn left on a red light into a one-way street, when is it legal to do so?

The correct option indicates that it is legal to turn left on a red light into a one-way street as long as traffic allows for the maneuver and there are no prohibitions against it. In Washington State, this specific situation is allowed by law, but it requires that the driver ensures that the turn can be made safely without interfering with other traffic. It's important to yield to all other vehicles and pedestrians already in the intersection or crosswalk. This rule is designed to facilitate traffic flow while maintaining safety, reflecting the state's flexibility for drivers in certain circumstances.

Other options are less applicable: a left turn sign being posted does not necessarily negate the permission to turn left on red, as specific regulations pertain to the overall traffic rules. Waiting for a green light generally applies to standard left turns from two-way streets, not one-way streets. Lastly, requiring a green arrow explicitly limits when left turns can be made, which is not the case in this specific situation involving a one-way street.