Heritage and conservation register

As a timber truss road bridge, it has strong associations with the expansion of the road network and economic activity throughout NSW, and William Bennett, the Commissioner for Public Works responsible for construction of many of the bridges.

Old PWD trusses were the first in the five-stage development of NSW timber truss bridges. Constructed from timber to conform with the 1861 parliamentary decree that local materials should be used in public works, the trusses took advantage of the high quality hardwood that was available in NSW. The design is essentially a copy of the European timber truss bridges that had their origins in the work of the 16th century Italian architect Andrea Palladio.

Clarence Town Bridge is located in the Hunter region, which has 15 historic bridges each constructed before 1905, and it gains heritage significance from its proximity to the high concentration of other historic bridges in the area.

In 1998 there were 2 surviving Old PWD trusses in NSW of the 147 built, and 82 timber truss road bridges survive from the over 400 built. The Clarence Town bridge is the oldest surviving timber truss bridge in NSW.

The Clarence Town Bridge is a representative and rare example of Old PWD timber truss road bridges, and is assessed as being of State (and possible National) significance, primarily on the basis of its technical and historical significance.

The main spans are supported by twin cast iron cylindrical piers braced with iron stiffeners and provides a single lane carriage way. The minimum width of the carriage way is 4.6m. A timber post and rail guard rail extends the full length of the bridge.

Timber truss road bridges have played a significant role in the expansion and improvement of the NSW road network. Prior to the bridges being built, river crossings were often dangerous in times of rain, which caused bulk freight movement to be prohibitively expensive for most agricultural and mining produce. Only the high priced wool clip of the time was able to carry the costs and inconvenience imposed by the generally inadequate river crossings that often existed prior to the trusses construction.

Timber truss bridges were preferred by the Public Works Department from the mid 19th to the early 20th century because they were relatively cheap to construct, and used mostly local materials. The financially troubled governments of the day applied pressure to the Public Works Department to produce as much road and bridge work for as little cost as possible, using local materials. This condition effectively prohibited the use of iron and steel, as these, prior to the construction of the steel works at Newcastle in the early 20th century, had to be imported from England.

Timber truss bridges, and timber bridges generally were so common that NSW was known to travellers as the "timber bridge state".

In 1881, a Clarence Town resident defended the need for the 'Brig O'Johnston' and described the bullock and horse teams hauling timber, maize and other produce around the district ('The Maitland Mercury, and Hunter River General Advertiser', 10/12/1881, p. 4).