Road/rail bridges in New Zealand have been and are of three types:
- Single shared deck. The most common type but also the most difficult to operate as it disrupts train and traffic equally when one mode must have exclusive use. Bridges either had bridgekeepers with gates at each end to close off the traffic, or else trains were subject to a 10 km/h maximum speed in order to ensure there was no hazard to other types of traffic given the length of some of the bridges. Although several of these bridges are still in place around New Zealand, there are only three currently active including the Taramakau mentioned later in this series. When that is converted to rail-only use, probably next year, the two on the Taieri Gorge Railway will be the last remaining operational in New Zealand.
- Double decks. Three were built in the early part of the 20th century and all of them had the road on the lower deck and the train on the upper deck. In all cases the road deck was for a single lane of traffic. All three still stand but none have both decks in use for road and rail. The Awatere River bridge on the MNL was converted to rail only use in the early 2000s. The Ongarue River bridge on the Stratford Okahukura Line has only been used by road traffic since the line was mothballed about five years ago; and the Ohinemuri River bridge at Karangahake has had the upper rail deck removed some 25 years ago and replaced by a pedestrian bridge as part of the Hauraki Rail Trail.
- Parallel decks. Two were built in the early part of the 20th century and a third was constructed about three years ago at Arahura as mentioned later in this series. These bridges have substructure (piers) that are shared between two separate decks (superstructure). The only real disadvantage compared to separate bridges is the need to achieve a similar alignment and height in the road and rail. The first two were respectively at Inangahua Junction (still dual use, with road since the mid 1920s and rail since about 1940) and Westshore (built around 1930, currently only the road deck is used and only by pedestrians, although the rail line is still in place).
The branch line from Greymouth to Hokitika and Ross dates from 1879 when work first began but it didn't get to Hokitika itself until 1893. Then a few years later in 1901 it was decided an extension further south was a good idea and the line was opened to Ruatapu in 1906. The final section to Ross was finished in 1909. This remained open for 71 years until the railway south of Hokitika closed in 1980. The line to Hokitika as it remains in use today has therefore been serving its district for the past 123 years. Although there are still sidings nowadays at Kumara and Houhou, as far as I know the only source of traffic for the line is the Westland Dairy factory right at the end. The siding there predates the factory and was probably built to reach a nearby sawmill.
The line originally had four combined bridges of which only one remains today, at the Taramakau River. A replacement road bridge at this location is going to be built starting later this year but the original will remain in use by trains. This article documents the four bridges. One of the original four bridges at Arahura was replaced by a new parallel deck combined structure.
As the railway heads south from Greymouth the first combined bridge location is at New River between the 12 and 13 km pegs. This is Bridge No. 11.
My historical notes (compiled and published 22 years ago) said it was bridge 12 but as that location can be seen further south, this must have been mistaken. Apart from that the only information I got was that the bridge was originally built with five spans with a total length of 204 feet (about 60 metres). The new road bridge was built alongside and opened in December 1937. By taking a look at the Google street view coverage we can see that the bridge photographed at that time (2009) appeared to fit this description, with it having one very short span at the southern end, three Howe Truss spans and another span (supposedly the longest) at the north end. Both the visual inspection and the Google ruler cast doubt upon the length mentioned above so it is possible there is another error there or else one of the ends was filled in at some stage with the overall length possibly more like 50 metres. I understand the bridge was rebuilt sometime between 2010-2013 and therefore no longer has the Howe Truss spans upon it. This has been the case with a number of bridges on the line since Kiwirail was renationalised in 2008 and there are now not remaining any Howe Truss spans anywhere on this line, or supposedly anywhere in the Kiwirail network.