Comment by lisper

> Couldn't he just route the cable via a pulley (or series of pulleys) to navigate the curves?

Yes, that is possible. But...

> Admittedly would fall foul of requirement #2.

You got it.

There are all kinds of other problems as well. The train will make a very sharp turn every time it hits a pulley. It's hard to attach something to a cable in such a way that it can reliably go over a pulley. Yada yada yada.