While plenty of new buses, trains, trams and subways are integrating more widely accessible features, inspiration can come from a concept like this Bus Bell by Jinwon Heo. It's common only to find one or two handicap buttons in public transportation carriages, and this designer's vision is to put these everywhere.
Indeed, everywhere you would find your regular 'Stop' button, an accessible button would be immediately adjacent. A passenger without special needs would press the red square that pictures a standing person; meanwhile, someone who is pregnant, in a wheelchair, or with a walker, a cane or a stroller would press the larger white button beside it. With that alert, the driver would know to slow down with more care, to lower a ramp, or even to halt next to a slope for a handicapped passenger's convenience.