The Polynesian Truss is typically used for building roofs, but I made it into a bridge.

This bridge is made out of Quartz with a wood decking.
Quartz was used because Iron has no stair or half slab blocks

The span between the supports is 31 tiles, overall bridge length is 33 tiles
Bridge is 7 tiles wide and features a 3 tile wide wooden walkway.

These can be nicely chained together with a 1 tile overlap.