The 1889 Hawkesbury River Bridge, Long Island Tunnel, Woy Woy Tunnel and the heavy earthworks and tunnels of the Cowan bank were the key engineering works on the Sydney to Newcastle rail link (The Short North). Together they demonstrate a high degree of engineering achievement in building a railway line in difficult and dangerous terrain. The 1889 Hawkesbury River Bridge in particular was a major technical achievement at the time: it was the fourth largest bridge constructed in the world, one of its caissons reached 49m, had the deepest bridge footing in the world and it was the longest bridge in Australia, pushing bridge design and construction techniques to the limit. The bridge was also the first of the American designed truss bridges that were introduced to Australia in the late 1880s and 1890s and thus the first to utilise the American principles of lightweight bracing, pin joints and eye bar tension members. It was the only steel trussed bridge of its type in Australia when it was built and the first major use of steel for bridges with previous examples being built in wrought iron. Its remains are tangible evidence of the change in engineering technology from British to American at this time and the decline of John Whitton's British based design influence on the NSW railway system. There is enough extant fabric in the remaining abutments, piers and the Long Island tunnel to demonstrate the engineering achievements of the original Hawkesbury River crossing.