Not sure about US but in London there is citymapper that has been doing it for at least 2-3 years and I remember that at least since 2011 there were single apps

Not sure about US but in London there is citymapper that has been doing it for at least 2-3 years and I remember that at least since 2011 there were single apps doing it. Citymapper is servicing a lot of different cities around the world. So I'm quite skeptic about yet another startup trying to disrupt this field..