Number 12 bridge railway accommodation bridge at NZ 191 297

Number 12 bridge is a railway accommodation overbridge built in 1842 by John Storey of Darlington for the Bishop Auckland and Weardale Railway Company, with The Shildon Works Company as the contractor.

The bridge is made of cast and wrought iron, featuring a timber deck and stone abutments. It is designed as a lenticular beam bridge that spans the railway cutting at a skew angle. The structure consists of iron lattice side girders supported by stone abutments that rise from the cutting. These girders form a single lenticular truss, which gives the bridge a humpback profile due to the timber deck being attached directly to the upper chords. The bridge has a span of 86 feet 3 inches (26.29 meters) and includes a timber deck resting on timber and iron cross joists.

The main top member of the truss is made of H-section cast iron, while the bottom member is a wrought iron flat link chain. The trusses have twelve panels with 11 verticals made of round bar, featuring diagonal flats that alternate in rising and falling. An additional lower bottom member made of square bar connects to the chain of the truss using cast clamps that support the cross tie-rods. The bridge also includes horizontal and vertical cross bracings made of wrought iron flats.

The stone abutments are constructed from squared, tooled blocks, with faces that slightly break forward beneath each girder. The truss hinges rest on stone or concrete blocks with angled tops, positioned back from the abutment faces. The timber parapets have been renewed, and the timber deck was replaced in 2009.