As Aeonwing mentioned there are different definitions for astral projection.
Atral projection for me is the semi-conscious projection of consciousness into an external space, or a space I perceive to be external. I am still very much present in my body.
I define an outer-body experience as etheric projection.
Now, astral projections is much more simple than people make it out to be. Etheric projection is much more difficult.
I don't think I could do either on a bus. It would be too noisy and my focus would not be at its maximum/ I would also not be able to physically relax.
It is my opinion, and the opinion of others, that the best time for projection is later in the night, or early in the morning when you have little distraction from the outside world. (Unless you live in the middle of nowhere.)
Sometimes you are fine, other times the sounds of cars, people, schools, TV etc. all get to you and effect you aversely.
Is it safe? Hard to say. Always practice AP after banishing/setting up a sacred space, if you can do that on a bus I'd be impressed.