[bluGill]

There is good reason they don't do that: trains derail once in a while, your plan means the following train will hit that train and so the accident is worse.

Part of the answer to that is better track maintenance. However that isn't a perfect answer and so we need larger gaps.

Note that cars on the freeway are normally much closer together than is safe as well. If cars maintained a safe following distance we would need 5 times as many lanes. (you know the massive freeways in Huston that urbanists like to show as bad: that is about the correct size of freeway for Des Moines, Huston needs many more if they want to be a car oriented city)

[TylerE]

I'm not even sure derailments is the worst flaw.

As soon as one train has to slow down, you're going to get the mother of all cascading effects - trains are slow to brake, but their acceleration is quite a bit slower than that, and you'll be limited to, at the very best, the acceleration of the slowest train in front of you.