The back end
Me atanding at the foot of the forward stairs one day, as we were boading disabled passengers at the front and sending the able bodied passengers up the back steps, rather worried looking woman comes up to me and tries to go up the front steps.
I stop her and say excuse me madam would you mind going up the back steps please as we are putting some disabled people on at this end. She looked at me in complete confusion and said, "Which end is the back?"