Sunday, 17 May 2015

Otago Central Railway: Wedderburn Highway Realignment

Although the Otago Central Railway had few changes in alignment, roads around it were realigned many times. One of the more interesting changes is just north of Wedderburn where the map dated from 1939 confirms that the highway was then located directly south of the railway rather than north today. As part of the highway the overbridge with railway number 66a was constructed and still exists on the route today although now bypassed. The highway realignment eliminated this bridge and a level crossing, the level crossing was very close to the railway summit of 630 metres which is the highest point on the whole of the Otago Central Railway.


The Wedderburn map (an extract from an NZGS map of 1939). The section of highway realigned is in the upper section of the map where the highway crosses the railway next to the words “F.McCarthy” and then crosses again further up near “P.Darling”. But whether the latter (northernmost) crossing was on an overbridge at the time the map was drawn has yet to be determined as the alignment shown actually resembles the current alignment with a level crossing due west of where the bridge actually is.


My map showing the entire section and the old and current highway routes. Bridge No.66a clearly is shown, along with the present alignment of the road to miss the overbridge entirely. Since the bridge number indicates it was not original, it is possible that where the road goes today, due west over the overbridge, may also be the original route that the road followed, or close to it, at a level crossing. Central Otago District Council's bridge inventory lists the bridge as "[bridge no.] 108 [ward] MANIOTOTO [roadway] OLD SH DOWN FROM COAL PIT ROAD [waterway] RAILWAY" implying this may still be a public road. An interesting point is the extra land set aside at the summit which suggests provision may have been made for a summit siding.


WedderburnN-Br66The GE shot depicting Bridge No.66a which still exists today. The Department of Conservation’s CASN 137 document describes it as follows: “Bridge 66, the road overbridge for State Highway 85 north of Wedderburn, is a 1966 pre-stressed concrete bridge. The abutments of the 1900 bridge are still visible, but are plain concrete foundations which probably held wooden piles. It does not require any special historic consideration. The highest point of the line (2029 feet, 612 m) is just north of this bridge. Bridge 66a, a private concrete overbridge, is very similar to Bridge 66.” So most of the description is actually the similar 1966 bridge further south. But the comment clearly implies Bridge 66a is now in private ownership, and further to that, Bridge 66a was almost certainly built first because this section of the highway probably is much earlier than 1966 and because there was already an overbridge at Bridge 66 dating from the original line construction. How much earlier Bridge 66a may have been installed is unclear because maps between 1939 and 1970 (by which stage the highway had been realigned) are hard to find. But my guess is the S bend in the highway needed for the bridge does imply it was installed well before 1966. However the number assigned to it (66a) strongly suggests it was added sometime after the line opened, certainly after the original bridge numbering sequence was assigned to the line. If that were the case then a level crossing at this location must have preceded the bridge, and this level crossing may well be at the location of where the road currently crosses the rail trail, shown above as a black line. There are earlier Naseby Survey District maps of this location but they are ambiguous in this area. But my guess is that they show both crossings via the cadastral map land boundaries and therefore leave unanswered the question of when the bridge was actually installed. The map revision dated 1954 still shows the highway in the old position.

UPDATE: I received information today including photos of the bridge and the information is that it appears to have been installed in 1950. Clearly at this time the realignment of the highway was still some years away. Whether this part of the highway was ever sealed is another question naturally, as it is not in a sealed condition today. The deck of the bridge as it now stands does not show any sealing. The way the bridge was installed is not commensurate with the needs of a high speed highway, as with the sharp bends it has been done in the cheapest possible way to make the shortest bridge, but as the line where the bridge goes over is in a cutting, the cutting may have caused visibility problems for traffic approaching the crossing. It does appear that the bridge is in private ownership along with the road today. Also it seems more likely the black line route marked would be where the railway went prior to the bridge, as this is clearly marked out in survey boundaries and on private land it would be unlikely to be formally surveyed. The location of the crossing would have been chosen to improve visibility being well clear of the cutting which can be seen on the above map and at right angles to get the best view overall. The use of the different areas of road isn’t so clear as of today but there may be still some use of the bridge but as we can see the old level crossing route is very clear and indicates it likely is still being used also.