RMXP and RMVX: Go ON bridge and BELOW bridge

Kinda complicated, uh, I'll do some kind of crappy ascii art here, maybe you'll understand:

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Alright so the red part is a bridge in a city, the green lines are the way to go over the bridge, this way you are seen ON the bridge, and cannot go off it by going up or down when you are ON The bridge, and the blue line represents the way to go UNDER the bridge, and you cannot go more left and more right then the limits of the bridge, and in this way, the bridge is ABOVE you, so is the graphics.

I saw this done in a game made in RM2k or RM2k3 idk for sure, called The Way (in a city called Estrana). I used rm2k to see how it's done and I understand the concept, and I tried to make it in RMXP too, but failed, can somebody help me? Or is there an easier way to do this via scripting?

Thanks in advance

EDIT: In rmvx I though about making those tiles passable and making switched events that are same as player (so that player can't pass) and making events go above and under the player if the player has switch BELOW BRIDGE on, but I don't know how to make the player be below the bridge, the player's sprite be below the bridge sprite
In rmxp I have no idea how to make this

I evented a bridge ages ago in RMXP which you can take a look at: http://www.mediafire.com/?z21ztrm3nij
Good luck working it out ^^

P.s. if you also want events to use the bridge you probably have to script the solution.

*hugs*

Yea I didn't think about that one, but using that method, I can't make railways, and how will I do if I'm using a custom tileset with a big bridge graphic?

Here's what I mean, download the way ep 6 http://www.crestfallen.us/download.html here, and if you have rm2k you can open it with it, and I think npcs did go under the bridge, at least in a cutscene (that was in episode 4, but this effect was used there too). How could they make that work?

Oh and an idea, would it work using an image over the scene? and just event the parts out?

thanks for the fast reply

You could use pictures or a picture precisely placed over the gap if you wanted to use it in a cutscene and show NPCs only walking under. You could use events and place each tile where the graphic of that gap is then an extra row on each side (to detect if someone is stepping there) and use conditionals to switch the height of the those tiles if you want just the player to walk over/under it. That's how I do it in VX anyway. Easy stuff. I guess it could get laggy if you happen to need a ton of tiles for the bridge in events though they're just graphics.