The By-pass consisted of 4km. of dual 3 lane carriageway with associated structures costing a total of £2.3 million. It was constructed between July 1968 and April 1970, the main contractor being Robert McGregor & Sons Ltd; the earthworks Sub-contractor was Richards and Wallington. On completion, at that time, this was the first 3 lane motorway north of the M1.
Erecting 30 ton girders
The scheme was basically constructed on the same alignment of the existing Trunk Road A1 dual carriageway by-pass, built in the 1930's but with improvements to the horizontal and vertical alignments. The contract included the construction of five main bridges, one being over a railway. All the bridges were founded on spread footings, four of them had pre-cast prestressed beams, two of the decks being traversely stressed on site. The remaining bridge had steel 'I' beams and was the longest single span bridge that had been designed in Durham. The span was 150 ft. (46m) and had a skew of 33° - each of the 8 beams weighed 30 tons with a pre-camber of 280 mm. This bridge carried the bifurcated north carriageway over the southbound carriageway of the A1(M), being the future link road to the Tyne Tunnel.
Even in the 1960's this section of the A1, adjacent to Washington New Town, carried substantial volume of traffic, particularly at peak times, being the main feeder into Newcastle from the south. Difficult traffic diversions onto existing single carriageways had to be organised in sections as the work progressed.
The Contract Drawings showed 12 disused mine shafts within the site, some had been extinct for nearly a hundred years. Only two shafts were found and the NCB required proof of previous back-filling by sinking bore-holes. After proving, the shafts were capped by massive R. C. slabs, 600 mm. thick, 35 m. x 35 m. approx. in plan.
This was probably the first contract let by the Durham Sub-unit.