[PhantomGremlin]

Exactly my question. It's 9000+ feet long. Put a lighted red X on it every 1000 feet. Or, maybe Xes aren't the answer, but there must be some technique to produce a startling visual warning.

It's probably a situation like Chesterton's fence. There are probably good reasons for not having the Xes. At least I hope so, I hope it's not just "that costs money and then we have to maintain it". The money can't be an issue. How much would 500 or 1000 deaths cost? How expensive are all the other proposals which have been mentioned? Those aren't cheap either.