I was getting on a train on the Northeast corridor this morning. The kind with the self powered cars and no engine. Noticed there was a cable on giant insulators between cars, hanging down in a loop and connecting the cars about a foot above people's heads if they crossed between cars. So there's a 12,000 or so volt cable running a foot from people's noggins. Will never look at crossing between cars in the rain quite the same way. Insulation can have cracks

(There's also a rubber seal between cars, but those are generally not terribly water tight.)

Population control, perhaps?