[SrDanielPonces]

I know Krystian already answered, but:

Depth of the Bridge (1/255 multiplied by 256)
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The depth of the bridge is important because it has the role to simulate the new ceiling when lara is belove of it, other to creare a wall with height between the up surface of the bridge and the down surface, set by depth.

By default (if you type 0 as depth) the depth is one click, like it was in old level editor.
Now you can set also values lower than one click, since the units for depth are 1/16 of game sector. This means that one click is 4 units.
In this way you can have very slim bridges, a nice chance for hanging footbridges, but also a very depth bridge, useful to simulate the collision of some big static objects placed on the floor, avoidin that lara was able to pass down of them.