Personally, I never have buses with more than 10 people at any time. Yet I cover all my cities in bus lines with a 30s frequency to feed my trains. I offset their -x00.000$ loss by making a goods line to the cities too which usually pulls 1 million or so.
What baffles me more is how train demand fluctuates. I’ll have 40 million in rail income one year and 29 million the next. Are those just bad years for voyages by train?