Regenerative braking on trains seems like low-hanging fruit these days.  Ah, yes, just did a bit of Googling and apparently it is standard equipment on most new trains:<p><a href="http:&#x2F;&#x2F;www.climatetechwiki.org&#x2F;technology&#x2F;regenerative_braking_in_trains" rel="nofollow">http:&#x2F;&#x2F;www.climatetechwiki.org&#x2F;technology&#x2F;regenerative_braki...</a><p>Older, especially freight, trains where all power comes from locomotives still tend to lack regenerative braking though.