Bulga Bridge is a Dare type timber truss road bridge. It has 2 timber truss spans, each of 32.0m (105ft). There are 3 timber approach spans at one end and 2 at the other giving the bridge an overall length of 129.2m (424ft).
The super structure is supported by sheeted timber trestles and provides a carriage way with a minimum width of 5.5m. A timber post and rail guard rail extends the full length of the bridge. The underside of the bridge deck has been strengthened with steel tension ties.
Strengthening of deck with steel tension ties. 2003/2004 - Emergency works undertaken requiring pier replacement, driving of new piles and a second row of piles.
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.
Harvey Dare, the designer of Dare truss and other bridges, was a leading engineer in the Public Works Department, and a prominent figure in early 20th century NSW.
Timber truss bridges, and timber bridges generally were so common that NSW was known to travellers as the "timber bridge state".