I feel very strongly that if a teenager is old and responsible enough to take the bus on their own, they are old and responsible enough for a smartphone. Furthermore, it's actively harmful to send your kids out into the world without the kinds of modern tools that would make them safer and more independent.
As for "phone died," well... just find a place to recharge it. It's not particularly difficult these days and I can't actually remember the last time my phone died on me when I needed it.
OP is a really cool demonstration of what we can do when everyone carries a computer in their pocket. Uber in the US has something similar with airport shuttles. Why should we handicap new, shiny things to make them usable without a phone?