Here's what I'm thinking, idea-wise. I want to make a skate park, and I want, in the main tube, a board that will travel the tube - a train, so that it can't be slowed or reversed. I will "path" it so that it's a trick ride, but I don't want the board to continue on the trick path if the original rider is lying in a gutter, bleeding out. So if he falls off, I don't care if the board rolls to the next path_corner - it'll be close by and look natural. But once the train triggers the path_corner, I'd like some entity to know there is no rider. So I need to trigger something to "kill" the train. Keep in mind that I'm not sure if "Kill Target" will remove it or reset it. I'm looking for the resetting of the train. I'm thinking that the train turns something on with the path_corner that is just in front of the path_corner. That "thing" is only on for a second, and if the player is on the train, he'll go through it. If he goes through it, the train is allowed to continue. If he's not on the train, he doesn't trigger it, and the train is reset. I'm also thinking that there needs to be two "somethings" in front of the path_corner, so that if the player is on the train, and proceeds through the first something, it turns off the second "something". The second "something" being the thing that resets the train.
Reading what you've written, I can see the concept you're going with. The forseeable problem in your scenario, for my map, is that it's multiplayer. And the trigger_onces would all be on at the same time. Someone else could conceivably reset the train by stepping or jumping through a trigger_once that is further down the line. I did not think of killing it before the path_corner, though, and will give that alot of thought. What I'm proposing is that at each path_corner, the rider/non-rider train resetting mechanism is turned on for a second (two at most) and turned off as the train and rider move to the next path_corner. That way, the "action" is very close to the player, happens fast, and 99% of the time, a different player can't affect it. If a different player does affect it, people understand if it happens once in a blue moon. It's not an exact science. But if different peeps can stop the train all the time, people will know it's a crappy job.
I will read up on trigger_relays, onces, and multiples.
As a side question, I was thinking of starting the train with a tiny "AAAtexture" trigger that would reset after the train's journey was complete. Do I need to toggle this to make it "reset-able"? Is there a method for reseting the train without an "on/off" switch?
I appreciate the response. I like these problems as well, but it seems each time I create a map, I have one "problem" that is just bonkers and just a touch out of my league.