To be clear, Transportr uses OSM for maps, but not navigation. Navigation is provided by Navitia, a free (gratis) but not free (libre) service which uses a select set of available public transit services. Navitia doesn't take public contributions, instead you post a request to add a transit service, and a link to the data. They'll take a look, and decide whether they can/will. I was lucky and had my city approved, but my friend's was not.