I read someone said that the cities will rebuild the roads, so even that wouldnt be a lasting solution, although maybe it'd help establish your service, it really depends on how the game deals with it, there may be a fundamental reason they arent using it, and the road being replaced will see them return to that mode.
Im not a huge fan of the steam forums, but from the little amount i did read on there (mainly expecting to see a bit of a backlash tbh, which i think might have happened as there were people saying they'd got over the initial issues and are still enjoying it) i did catch someone saying that the location of the train station is essential, but i didnt fully understand what that meant, without screenshots it was hard to tell, as its not like you can knock down their buildings and plant the station right in the center (at least you cant build a depot on them, havent tried demolishing but i doubt you can).
I also started a basic bus service, completely screwed up the placements of the stops so it'd go around the block to get on the right side of the road etc, but i had 1 person get on and thats it. No idea what was wrong, maybe i needed more buses to shorten the time, but i only ever had 1 person wait, its not like they gave up.
Im really going to have to go get OTTD and give that a few hours again, but its going to feel a bit bland in comparison, but its so much more complete and varied. Boats, planes, easily twice as many industries, vehicles, and competition to rival you. It more than makes up for being a much older game.