The long main line ran from Port Craig in southerly direction, parallelly to the coast, to the
Wairaurāhiri River In addition, there were of spur lines. The main line was surveyed with at maximum grade of 33 ‰ (1 in 29.5) and deep cuts and high
trestle bridges much more elaborately than similar tramways. The main line used four large wooden viaducts built around 1925. The
Percy Burn Viaduct is 125 m long and 36 m high, and was specified for the transport of the 80 t
Lidgerwood steam winch, which had been imported from the
United States as well as the heavy load of logging trains. During its construction, Australian hard wood was used, because it has a higher strength and durability than local timber. The trusses of the Sand Hill Viaduct consisted of round hard wood trunks, which were surrounded by less durable
sap wood. The other viaducts were made from sawn timber, of which the sap wood had been removed. The four viaducts are the largest logging railway viaducts of New Zealand. They are listed buildings and are preserved in a structurally weak condition. == History ==