The existing rail system has at least the following constraints:
* Uses steel-on-steel friction, rather than rubber-on-rock. Cars that can do both exist but are rare.
* Can only travel on the specially-prepared rails, not installed at the last-mile, related to the next point.
* Poor cornering and elevation changing.
* Difficulty in changing speeds (over a thousand meters and over a minute, compare to about a hundred meters and less than ten seconds for road vehicles)
* Very limited lanes, usually no passing. Track reservations will be voided if you aren't exactly on schedule.
* Almost all of the "intelligence" (both computer and human) is at one or both ends; the cars in the middle are all "dumb".
Which of these can reasonably be changed?