What the difference between electric buses behind each other in a tunnel compared to multiple rail way cars behind each other? One system is cheaper because th

What the difference between electric buses behind each other in a tunnel compared to multiple rail way cars behind each other? One system is cheaper because the units are mass produced far more often and the system is more flexible. Carrying around a battery rather then having complex high power electronics along the tunnel seems like a no brainier as well. Las Vegas is literally a first of its kind system, being a few month behind is not surprising or concerning. And the problems have to do with specific fire codes, not any inherent flaw in the system.