Thanks–I think it was the fact that the pylons could presumably be scaled that was making the sentence difficult to parse (I wasn't sure how they were meant to prevent access). That, and that the pylons themselves are also presumably "critical elements" of the system.
the pylon could be the target to disrupt the operation
Yes, but so could tracks on any high-speed rail, and in that case with considerably greater ease. In this case, the actual railway is sealed off from all but the most determined external forces, who would be able to do just as much damage to a conventional train.
You don't have to worry about cows wandering into oncoming vehicles like you do with cars and trains. It's also harder for non-determined people with malicious intent to interfere with operations.
A determined attacker can, of course, scale pylons. But you don't have to worry about stuff like kids lobbing bricks from overpasses, or people pushing others onto subway tracks.