Use trains to transport passangers from town to town, and connect them to buses to shuffle people to their final destination. Have a network that connects the whole map (easier said than done, requires lots of capital) and I guarantee all your vehicles will be profitable.

This is why I like Simutrans: the passengers want to go from A to B.

By the way in Tycoon there was a bug (extra multiplication) that caused larger towns to generate insane number of passengers. It was copied all the way to OpenTTD then it was turned into option.