To show that you may only proceed in the direction indicated by the arrow in your lane.
Choose the correct lane in time to travel in the direction you want to go. • Make sure that other traffic is obeying the mandatory direction arrows in their lanes. • Check your blind spot before turning right to see that a vehicle in the lane next to you that is supposed to turn right (because of the mandatory right-turn arrow in that lane) is not carrying straight on.
Where to expect it: On any road before an intersection.
