Big difference between heavy rail and light rail trains.

Also, TANSTAAFL: regeneration to a battery recovers, usually, half or less of the power removed by acceleration. That helps, greatly, but you don't get back what you put in.

If you want to make sure regeneration gets captured, in the absence of enough traffic to ensure other trains in a power block are using it when you're generating it, adding batteries and ultracapacitors to power substations is a well-known practice. Much bigger batteries can be used there than on the trains themselves, so much more of the regeneration can be captured and delivered to other trains.