Small bridge

[Paddy]

The problem with RR ties in your method is you will have loading on the two you are driving on. The strenght of a beam is HHHxW/l. That is the height cubed x width in porportion to it's length. So tall beams are good. RR ties are nearly square, 9" x 7" by 9'7" long. Look at a floor joist, note H is quite large!

The size of the beam is reduced as the length is reduced. Reduce the span as much as you can. The creek bed may be large, but what is the water flow?

 

[Nasty135]

BrainZ, One Telephone pole cut up into lengths would work IMO you would need four lengths for the beams then your planking on top, Quick and dirty it would last a good while... But not like two beams and a concrete footer

RR ties isn't as good an option IMO...weight wise , although it is only 5' span

JusT MY 2 cents