If HSR would have ever been built in the US, the security measures would have been similar to flying. There's a lot more people on a moving train and it would b

If HSR would have ever been built in the US, the security measures would have been similar to flying. There's a lot more people on a moving train and it would be moving at dangerously fast speeds. So it's not obvious that getting on one would be so much easier and faster than onto an airplane. Certainly the one door boarding/deboarding is a problem with airplanes, but since the world has transitioned away from 747s and toward 737s, this issue isn't particularly troublesome.