Animated objects have no collision as such while in motion, I believe your original question involved an animated treadmill which would have been solved by an invisible platform and using playerassociated condition, check out the lift scripts, and have the platform follow a waypoint.
You would have to give more info about the animated bridge for anyone to help with a workaround, is it a drawbridge or whatever?
Animations do have collision at the original point on the first frame of animation, this is where the collision box is created in the way doors work, you have to think in reverse, so if your last frame is where you want collison to be you have to have that frame at the start of your anim, a way around this may be to export your model with the last frame put at the start of your animation, you would skip this frame in your entity fpe, for example your anim frames would be anim=2,100. I did something similar with walls for a maze in a game before..
Use something similar to this.
;Triggers
:state=0,activated=0:state=1,setframe=0,sound=$0
:state=1:incframe=0
:state=1,frameatend=0:state=2
:state=2,activated=1:state=3,sound=$1,colon
:state=3:decframe=0
:state=3,frameatstart=0:state=0,setframe=0
