I see. Having bus=yes or bus=designated should override motor_vehicle=no, vehicle=no, or access=no as the most specific mode should take precedence in routing software.

If something is mapped as highway=busway, as is the case here, I think you can safely remove motor_vehicle and vehicle access tags without causing routing issues for other vehicles.

It might be more of a problem around bus stations where the entry signage on a highway=service road is "no entry except buses" or "no vehicles except buses". Access tags are supposed to follow legal restrictions and in both of these cases, vehicle=no + bus=designated is the effect of the signs. Can I assume that this is the Brouter implementation used in Busmiles.uk's snap to route function?