Compared to 12mph for trains, private motor vehicles are often slower than 10mph and even slower if you count door to door times rather than only "time on road".

In my experience (Sydney, Australia mostly) once you include waiting time the trains don't even get to 12mph over short distances. But for non-trivial distances (anything over 30 minutes) the average speed here jumps dramatically thanks to express and station-skipping trains (we have >4 tracks on much of the network). For longer journeys trains make a lot of sense, especially since I can take my PRT on them.

But then my personal transport weighs in at about 100kg all up. I have 5 bicycles, you see and I already have personal rapid transit. When I can't ride my bike I often get quite impatient as I'm not used to waiting and going slowly for no readily apparent reason, since bicycles are fast, door to door and if you're in a hurry it's legal to go as fast as you're physically capable of (for the most part). The cost also doesn't bear thinking about, especially if you're a motorist. I trust you're familiar with Ivan Illich's ideas?