Question Automated wagon addition and removal.

Hi all,

I need help because i'm pretty new with command block and i have no idea of how can i do what i need to do.


Like you can see on this picture, i have rails on the ground and also a warp portal (under the ground, not on the picture) at the end of the rails to another world map.

So i want to know if someone can tell me how to add automaticly a wagon everytime someone take the wagon on the rails (sorry there is no wagon on the picture, but imagine there is one where the player is looking at).
And also a way to make this wagon disappear when he gets off the wagon (or if it's too difficult) reach a certain point (on the other map).
For information after the warp portal the player appear on the same wagon and continue to move forward on another rails on the other world map.

Really thanks a lot for help and sorry if my english is not perfect so if you need some explanation tell me and i will do so.