HO scale Road Bridge 16 ft wide by 40ft long. Based on standard plans for the state of Ohio from 1912. The deck is reinforced concrete, the side pony trusses and end beams are steel.
The model comes with five parts ( two steel truss sides, two steel end beams, one concrete deck ) to make painting very easy. The underside of the concrete deck was hollowed out to reduce the cost by $20US - you can easily create a solid concrete deck by gluing rectangles of 0.020" styrene into the recesses between the main beams.
A 16ft x 53ft version of the bridge is also available in Smooth Fine Detail Plastic for $95US:
https://shpws.me/SYrg
Instructions showing how to separate then assemble the parts are posted in the Forum:
https://www.shapeways.com/forum/t/road-bridge-ho-scale-steel-pony-truss-16ft-x-40ft-assembly-instructions.101843/
A magnifying headset (Optivisor) and a precision sprue cutter like the Intermountain BB-1015, Micro-Mark #82393 or UMM-USA GMT01 are required to cut the parts from the support framework.
https://umm-usa.com/onlinestore/product_info.php?cPath=21_28&products_id=3749