When waving down a bus for a flag stop, you must stand in a highly visible area, that is not obstructed by a parked car or some other immovable object. The bus must be able to pull out of traffic to pick you up, and if there is nowhere for the bus to safely do so, they will not be able to accommodate your requested flag stop. A bus also cannot stop at an intersection to pick up passengers, and will not stop for flag stops in the downtown corridor (Walla Walla Core or the Walla Walla University core on College Avenue between 4th Street and Whitman Street). Below is an image that shows in general safe places to flag a bus down might be.

As you see depicted, a bus cannot pick you up if you are waiting on a closed street, at an intersection, or if you are hidden by a sign or tree. This does not mean that you cannot wait for a bus under a tree, only that as the bus approaches, you need to step out to make yourself fully visible as you flag the bus down. Always look for an open and easily visible area that has at least 50 feet of clear space directly in front of you that would allow your bus to safely pull in to pick you up.

If the driver can see you, but you are not located in a safe place for them to stop, they will try to find a nearby safe place to stop, but this will mean that you need to walk to where the bus parks. A bus will never allow you to board while they are still in the traffic lane.