Idaho Code § 49-806: Lane use control signals.

When lane use control signals are placed over individual lanes, the signals shall indicate and apply to drivers of vehicles as follows:

(1) Green indication. A driver may travel in any lane over which a green signal is shown.

(2) Steady yellow indication. A driver is being warned that a lane control change is in process.

(3) Steady red indication. A driver shall not enter or travel in any lane over which a red signal is shown.

(4) Flashing yellow indication. A driver may use the lane only for the purpose of making a left turn to or from the highway.