I started this bridge a few years ago with plans to use it in an Urban skirmish scenario. I measured out some dimentions on the cardboard that would serve as the bridge floor and then constructed a wood frame around it. The ends of the bridge lay on ramps that form both the road and the river bank.
The road parts were made from pieces of Styrofoam glued to a CD. I carved the road slope and a notch for the bridge then covered it with spackle to make a smooth area for the road and cover up the foam texture. Once the spackle was dry I covered the whole thing with gray latex paint to seal off any exposed foam and act as a primer for later spray-painting.
I added some extra detail on the bridge with triangle pices acting like small butresses, but then got stuck for a year or two trying to figure out how to make a street light. Finally over the 2008 holiday I grabbed a couple of plastic "perl" beads and threaded them on a bit of wire glued into a dowel. It looked convincing enough so I secured it to the bridge with a nail and wood glue.
Now the bridge has been painted grey and the road black, and I only have to flock the river edges to consider it done.