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This is how diesel-electric locomotives work too.

They also use the electric motor(s) for braking, but instead of going into a battery it goes into a bank of resistors.

I think you meant capacitors. Resistors would just dissipate the energy as heat.

edit: Thanks for the correction. They do indeed use resistors and just dump the energy as heat. Unfortunate.

Hopefully this will change as supercaps continue to improve. Maxwell tech's modules are already used in light rail, and looks like some work towards smaller locomotives in Switzerland here:

https://www.osti.gov/etdeweb/servlets/purl/20823697

Nope, resistors. The energy is dumped as heat.

Dynamic brake

Capacitors have pitiful energy storage capacity. Resistors is correct, unfortunately.

To add to the other comments: https://en.wikipedia.org/wiki/Dynamic_braking

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