You have to make the spline no longer "adjustable to terrian" and you have to hold h + movement of the mouse to make an object float to where you want it to go. You can also use the "set height" option in the height editor to make sure that you have a flat surface for where the bridges meet.
And obviously you want to make your objects (bridge most likely in this case) no longer adjustable to terrain as well, so that way the cliff/terrain faces that intersect with it don't push the bridge/object up.
Sounds solid. I'll mess around with it. Thank you.