But one huge factor that you have to contend with is the randomness of the tragedy of the commons problem on public transport / shared transport. A train journey can be blissful to sleep on right until a loud group gets on and sits across from you and there's no seats available to move.
I think this is something that can't be overlooked, especially if you're talking about something like a short trip where if you don't sleep well en route, quite a large proportion of the trip time is going to be affected. Having a private vehicle where you can guarantee control of your environment is a really huge plus.