Very interesting! For anyone else that's curious, I found a Wikipedia article [0] with more information. It turns out that an "easement" can also be a right to use land that you don't own for things like roads and structural support [1], so it took a minute or two before I found it.

[0]: http://en.wikipedia.org/wiki/Track_transition_curve

[1]: http://en.wikipedia.org/wiki/Easement