Thanks, Jay Potter!
For curiosity, where did you find out about this? I try to keep up with railroad news-- particularly GE locomotive news-- to the degree it is possible from the general and railfan press, but don't recall seeing anything about this.
Any idea what it will look like? I'd guess that the batteries needed to store the energy recovered from dynamic braking of a heavy train coming down a long grade will be pretty big, so I have been ***IMAGINING*** a basically conventional-looking ES44 connected by heavy electrical cables to a "tender" with the batteries! But this is JUST my imagination (starting from my purely amateur's conception of the engineering issues involved).
Anyway, thanks for the information!