Adam,

I use a Garmin 276c. When I hit menu twice that will take me into Setup, from there I move to Road routing, then select Calculate routes for, then choose Bus, it's default setting is Car/motorcycle

It also has a custom road prefs. which I can choose to change my prefs. by moving the sliders toward the major road and medium roads but avoid minor roads.

Try looking around a little in the setup menu, there is a lot in there.

Good luck!