I thought Milwaukee Road used rotary convertors? I can see where adding power back into the 3,000 volt DC overhead would help a train drawing power in the same circuit, but to "make the meter run backwards" into the AC transmission line would require it to be reconverted from DC back to AC of the right phase and voltage.

I'm sure today's modern static convertors or high voltage AC overheads could handle regenerative braking easier. But how well is the commercial grid going to handle the wild variations from acceleration of HSP or a sudden surge of regenerative braking that suddenly drops out?

I won't argue that there is a huge advantage to regenerative braking, as I would much rather use that power than simply throw it away as heat. But - regenerative braking on modern freight trains in North America (assuming you electrified) has the same exact considerations as dynamic braking. You still have the 250,000 pound buff limit, and it is not a fail safe system.

Wonder what Caltrain is setting up to do?