[Dylan16807]

> You probably know more about this than me, but it looks like some lines do

I'm confused. Your phrasing suggests that you're adding in new and potentially conflicting information, but "many don't" and "some do" mean the same thing.

[londons_explore]

The missing piece of info here is that while most of the trains have the capability to do regen braking, it is generally ineffective because it can only be used if another train on the same section of track happens to also be accelerating at the same time.

That happens rarely enough that most of the trains, most of the time, do not effectively regen, and instead use mechanical or resistive braking.

[jeffbee]

There was chatter 20-30 years ago about using flywheels to bank the energy until needed.