Is there a way to make a zone passable only one-way?
I'm creating a race map and the point is to reach the 4 checkpoints, in order, to get +1 lap (nothing too fancy there ). The thing is, the way my triggers are currently set, players can just run to Checkpoint #4 and come back to #1 to gain 1 lap...
I'd like it so players cannot go back once they have reached a Checkpoint. It must not a real-physical barricade since it'd prevent other players from passing through it to access to the Checkpoint.

I'd probably do a check by giving the unit a custom value of the previous check point they passed and make sure they can't pass the same one or the one before that and only the one ahead of it.
You can use variables as well. It can do just the same.

Basic pesuedocode:
If unit passes first check point and the value is equal to the check point before, change value to 1.
If unit passes second check point and the value is equal to the check point before, which is 1, change the value to 2.
... etc.
But in check point 4, add 1 lap to the triggering player's overall amount of completed laps.

When the unit tries to go back after it changes value to the last check point it past, just move the unit instantly back on the track to a point offset the center of the last check point.

I didn't put this in Triggers Assistance because I was searching for a way to literally place an object that would only let players pass one-way through it.

Yeah, so far I haven't been able to accomplish that as well with the data editor. But it works with triggers. =/
But probably tinkering with behaviors, effects and the arc. Its what I tired to use to make it work.

I'm 100% sure I'm not good enough with those to be able to obtain such an effect.

Terrain wise you can have ramps and jumps, other things that makes it impossible to get around check point... it all depends on your map layout so far.

Another way would be to make it so that when you go to another section of track you enter a new section of map much how caves and world map share different maps.