I ran into this issue in recent years, the property where I put my pond has a pretty decent sized creek across the front half of it, I built me a riprap low water crossing while I did some planning, I seen a an old, heavy, lowboy trailer sell for very little and it didn't occur to me that that would have made a great bridge till after it was sold, facepalm,all it would have needed was some new decking. shat I wound up doing was go to a friend of mine that has a precast concrete plant, makes manholes, box culverts and concrete pipe and such, he wound up having a few over run 10'x6' inside box culverts that I was able to obtain for a fraction of the original cost, basically just enough to recoup his material costs plus a little. the biggest obstacle was setting them in place as the weighed about 20T apiece, I had three 6' sections giving me 18 ft of bridge, they were built to go under a 4 lane road so were plenty heavy built, I have crossed them with a d6 dozer several times during the pond building process, turned out to be the most economical solution for me. I would post some pictures but my iphone takes 3+ megabite pics and have yet to be able to figure out how to post one.
