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 one at Camerons mentioned below. 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 below. 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 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.
The second location of a combined bridge is at the Taramakau River as mentioned above, being Bridge 13, between 14 and 15 km. It is lattice girder steel with six spans each 121 feet long (total length around 220 metres). It is founded in the bed on steel cylinders which must suggest a heavy flow is a common feature of this river.
Because the bridge is on the main highway to Christchurch it has tended to get a lot of attention. Obviously while New River was easily dealt with, Taramakau has attracted more than 80 years of promises; for example in 1965 both this bridge and the one at Arahura were going to be replaced within five years. A couple of ideas that didn't make it were an extra lane on top and on the sides, because of insufficient strength in the foundations. Still, a clip on cycle/pedestrian lane was attached late last year for the West Coast Wilderness Trail even though the new bridge has been planned for building later this year. There was a bridgekeeper based there for many years, whose job was to close gates at each end to keep road traffic back, but this position must have come to a close with the reduction in trains as there is currently only one or two per day.
The gate at the south end is a prominent feature of this 1987 photo along with the bridge keeper's hut. The bridge was recently repainted red after being in this silver paint scheme for many years. The clearance shown as 3.44 metres in my picture was later increased to the present 4.60 metres by raising the top of the bridge and the overhead wires were also removed.
Here is an aerial view from Land Information New Zealand around five years ago.
NZTA says the new bridge will be about 30 metres downstream (to the left of this photo) and will also cross over the railway line with an overbridge to the south.
The third example of this type of bridge was until about three years ago found at Arahura River. It was originally constructed with seven 80 foot Howe Truss wooden spans and another seven much shorter plain spans just under 15 feet, giving it a total length around 200 metres. As far as I know it never had a bridgekeeper. The location is around the 31 km peg and it is Bridge No. 28.
The foundations of the original bridge were partly wooden piles and partly steel cylinders. Reconstruction brought along a new bridge which has the separate road and rail decks sharing the same piles in the riverbed. It is thus New Zealand's newest example of a combined bridge. The location of the original railway bridge is occupied by the present road bridge deck. One of the Howe Truss spans has been preserved in a reserve area adjacent to the south end of the bridge.
In this 1987 photo it can be seen some of the plain spans were at the south end with their wooden piles, while the first of the Howe Truss spans is resting on some iron cylinders. Probably these cylinders were placed in order to allow for where the water flow was heaviest in the riverbed.
Here is an aerial view of the old bridge from the Kiwirail ALCAM maps.
The replacement structure as seen in LINZ's aerial photography. A roundabout for traffic was added at the south end to combine a level crossing with a T junction.
The fourth of the bridges was immediately south of Hokitika and crossed the Hokitika River. This bridge was easily the longest of the four, having 16 80-foot spans and 76 20-foot spans, totalling around 850 metres, making it one of the longest railway bridges in New Zealand. The road across it was always considered to be a local road and the biggest problem for NZR was getting enough money from local authorities to pay for the upkeep of the road deck. It is interesting that the original highway bridge dating from 1878 in wood and replaced 1938 in concrete was placed at Kaniere, some 3 km upstream, where the length was able to be halved. One assumes the pros and cons of building the massive length at Hokitika itself was well canvassed prior to construction. The winning tender to build the bridge was confirmed in 1902 at 26,541 pounds, which today is equivalent to about $4.6 million. By 1909 NZR was demanding 150 pounds in annual maintenance contribution from ratepayers ($24,000) but a poll of the same ratepayers resulted in the Hokitika Borough Council offering 90 pounds ($14,000). By the time the bridge closed NZR could only demand $300, which was the equivalent of 150 pounds at the time decimal currency was introduced, and not at all the same as 150 pounds in 1909. This was clearly manifestly insufficient for such a long bridge in 1980.
Because of the cost wrangles, the bridge was one of only a few road and rail bridges that for all its life had transverse decking with the rails raised above the deck level. Think of it as a deck made up of railway sleepers with the rails sitting on top. In order to cross, a road vehicle has to straddle the rails. This is difficult with vehicles that have insufficient clearance underneath as some sports cars would for example. This problem was dealt with on most other road rail bridges where the money was available by laying an extra layer of longitudinal decking planks on top of the sleepers which brought the deck up to be virtually flush with the top of the rails, as you can see on the photo of the Arahura bridge above.
The arrangement of decking led to the locals calling it "the longest xylophone in the world" as the sleepers would rattle under the wheels of passing vehicles making quite a lot of noise in the process. By the early 1970s the road deck was in pretty bad shape but NZR was still only getting $300 a year while spending more than $7000. In 1977 the Ross Branch was proposed for closure due to the high costs of bridge maintenance; the actual date was set for November 1980 and $10,000 was spent patching the bridge up to keep the line open. The road deck of the bridge was closed to traffic in 1979 as it was by then unsafe. Tenders were called to demolish it in 1982 and the work was completed two years later. The TV film "Bad Blood" apparently used this bridge to film a scene of a police car heading south from Hokitika in 1981 (set 40 years earlier).
In the early 1990s NZTA decided to build a new highway bridge in the same location as the original and this appears to have opened around 1992/3. This resulted in State Highway 6 being relocated onto a new route between Hokitika and Ruatapu. South of Ruatapu the highway follows its original route. The new highway reused the railway formation from Hokitika to the Mahinapua Creek bridge,
