Regenerative braking in trains | ClimateTechWiki: "Employing regenerative braking in trains can lead to substantial CO2 emission reductions, especially when applied to full stop service commuter trains (8 – 17%) and to very dense suburban network trains (~ 30%). Regenerative braking applied to freight trains can also lead to CO2 emission reductions, albeit considerably lower than for full stop service trains (~5%)." - But that could be improved.