To warn that one or more concealed driveways enter the road you are driving on from the left or right in such a way that you cannot easily see the road or traffic travelling on that road.
Slow down so that you can stop or yield if there is cross-traffic that does not yield at the intersection. Remember that a driver of such a vehicle that joins your road from the concealed driveway sometimes also finds it difficult to see you.
Where to expect it: On any public road.
