I dunno...
Many trains in London still don't do regenerative braking despite the technology to generate electricity from motion being around for... checks notes... 194 years!
Many trains in London still don't do regenerative braking despite the technology to generate electricity from motion being around for... checks notes... 194 years!
Regenerative braking in cars also keeps a lot of brake dust out of the air. A pair of brake pads lasts about as long as the life of an EV.
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.
That happens rarely enough that most of the trains, most of the time, do not effectively regen, and instead use mechanical or resistive braking.
NiMH could have been attached directly to the rails.
Today, lithium batteries win for Watts per dollar, and perhaps custom made packs could also be attached directly to the rails.
But a cheaper solution is probably bidirectional inverters, allowing the DC generated by the trains to be fed back into the 3 phase national grid.
Unfortunately, all trains in London today cannot regen into the grid - they can only regen into the rails and hope that some other train on the same rail is accelerating at the same time to use the energy. By my estimates, that only happens less than half the time.
By the way, implementing regen on synchronous motors is relatively easy, IIUC, command a positive torque to the inverter and it draws current and line voltage gets pulled down. Command negative and opposite happens.