The Menangle rail bridge constructed in 1863 is the oldest surviving bridge on the State rail system and is of highest significance in the development of railway technology in the State. It is an excellent example of early bridge construction. The bridge is one of two identical bridges constructed for the NSW Railways, the other being over the Nepean River at Penrith. The Penrith Bridge was opened in 1867 but has been used for road traffic since 1907. The Menangle rail bridge is typical of British bridge engineering of the 1860s, the iron spans having been fully imported. Additional supporting piers were later erected under the spans so that heavier engines could be used on the main south line. The bridge is of national, if not international, significance as there are few such bridges still in use in the United Kingdom.