I've noticed many times (I think it happens every, or at least almost every, time an intercity line finishes a route) that passengers just disappear during the journey. For example, a train with 34/34 passengers arrives at the destination with 31/34 people, or a L'Obeissante arriving with 5/6 passengers when it started with 6/6.
What happens here? Are passengers dying during the route (seeing how they're all individually simulated, I don't think it impossible - but a few every journey?)? Or are they falling out at steep curves? :D

Well, at least I'm not the only one.
Maybe they're jumping out of the vehicle because they can get to their destination faster this way :). It's just a pity they only pay when they get off, not when they board.