Electric Train question....?

yes, absolutely true

regenerative braking it was called where I worked

A train going downhill could "pull" another train coming uphill.

Incredibly efficient. The technology has been around nearly a hundred years now.

On the Milwaukee, they had their own seperate high voltage line and the current was modulated via substations every 30 or so miles to keep it at optimum voltage.

The power was transmitted via the high voltage line at 110 KV AC current and rectified to DC for the actual trolley system.

I dont know much about the how the electricity gizmos work but the same line they used for providing power to the system also supplied power to towns along the line in western Montana and Idaho. It must have been transmorgified back to the single phase household current without too much trouble.

Yes. I'm not completely familiar with the application but it is quite similar to dynamic braking. Basically the electric motors can use the incoming transmission as extra braking to help slow the train. Answers member Rango may be able to explain this better as he operated electrics on the Milwaukee Road's Pacific Extension (through the Rocky Mountains and Pacific Northwest) before the line was de-energized in 1974.

Yes, it's called regenerative braking.

However, design is tricky. If the system is AC, regeneration must be in-phase with the AC power on the overhead wire. If there are no other trains in the area to use the regenerated power, the train must do something else with the power, so it still needs regular dynamic brakes with the toaster grids. Generally it's not practical to regenerate into the power grid, because the power grid is 3-phase and the train is regenerating single-phase or DC.

I believe that it works much the same as dynamic braking.In dynamic braking the traction motors are turned into generators.It pushes the armatures through a field to create retarding force.On a diesel electric unit that power is dissipated though a bank of resistors as heat.On an electric railway it is fed back into the power grid instead of being wasted.

As a side note i recently had a GE Evolution Hybrid unit #2010 in my train that used that generated power to charge banks of sodium chloride(yep salt) batteries.Then when the unit went back to tractive effort those batteries supplemented the main generator feeding the traction motors.The GE techs riding with me said they expect it to save at least 25,000 gallons of diesel a year per unit.