We did one, over a creek running through a cemetary. I can't remember the exact length of it. It was probably around 20 foot. Subbed it out. This guy was just a one man show. We helped him out setting it in place.
Gopher ...what an awesome site! I bookmarked it for future reference. We actually have a small bridge to build later this season. I don't know all the particulars yet but I'm sure that site will be helpful.
You're truly an asset to Lawnsite with all your helpful links.