So this is 100% my dysign inspired by a cattle crossing irl
Cattle Gaurd.zip

Just ignore the old posts that vanished.

Assuming my understanding of this device is correct, it needs to be a little wider to support the rails going through/over it, the rails are roughly 14 microblocks wide if you include the ties, in the case of vanilla and railcraft rails that can be increased up to 16 microblocks with certain skins.

the reference images i came across:
http://upload.wikimedia.org/wikipedia/commons/9/9e/Rail_cattle_guard.jpg
http://rhopkins.us/Route66/images/DSC_0777a.jpg
http://trainweb.org/chris/14amspeed84.JPG

Cattle Gaurd (2).zip
Is this better? I made it a bit wider, enjoy!