How is a closed reversible lane indicated?

A closed reversible lane is indicated with a red "X". This signal signifies that the lane is not available for use, and drivers must not enter or drive in that lane. The red "X" serves as a clear and universal warning that the lane is closed for traffic, helping to prevent accidents and ensuring driver safety.

In contrast, a green arrow would indicate that the lane is open for use, while a yellow diamond is typically used to convey caution about upcoming changes in road conditions or potential hazards, rather than indicating the status of a lane. Flashing lights can signal various conditions but do not specifically denote a closed reversible lane. Thus, the red "X" is the appropriate indicator for this scenario, providing unmistakable guidance to drivers.