Dunedin Southern Motorway

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The Dunedin Southern Motorway is the main arterial route south from the South Island city of Dunedin, part of New Zealand's State Highway 1. It is the world's southernmost motorway.

[edit] Route

From the base of Pine Hill and the southern terminus of the Dunedin Northern Motorway SH1 traverses Dunedin as two multiple lane one-way streets, travelling past the University of Otago and the CBD before connecting as a single multiple-lane road at the Anderson's Bay Intersection; a busy signal-controlled "T" intersection with SH1 and Anderson's Bay Road in South Dunedin.

From the intersection SH1 becomes a four lane median-divided road for 700 metres, crossing South Dunedin's main street, King Edward Street on twin overbridges, until near the Glen, just north of Carisbrook, where the road narrows to a two lane undivided road. To achieve this the southbound lanes merge into one, while the northbound carriageway gains a lane from an on-ramp originating from South Road. While this section meets most technical definitions of a motorway with full limited access including no pedestrian or cycle traffic, it is not currently designated a motorway by Transit New Zealand due to its short length.

SH1 continues south as a two-lane limited-access road past Carisbrook and the suburb of Caversham. The South Island Main Trunk Railway parallels SH1 along this section along the east side of the road. This section of road is known as the Caversham bypass, and is subject to congestion during the morning and afternoon weekday peaks, being a bottleneck between the four lane sections of SH1 immediately to the North and South.

SH1 from Anderson's Bay to Barnes Drive, at the suth end of Caversham, is signposted for an 80km/h speed limit.

Map showing the Dunedin Northern and Southern Motorways (marked in red - other parts of State Highway 1 are marked in white).

At the base of Calton Hill, SH1 intersects with Barnes Drive at a signal controlled intersection. SH1 becomes a four lane road at this intersection before climbing up over Calton Hill to Lookout Point. This section of highway is residential arterial road, with houses upon both sides and a 50km/h speed limit enforced by a fixed speed camera about one third of the way up the hill, though there are proposals to widen this road to connect the Caversham bypass with the motorway to the south.

Near the crest of Lookout Point, SH1 retains priority through an off-set intersection with Mornington Road and South Road, before heading southwards over the crest. At this point the official designated motorway begins, with a concrete median divider and an increase in the speed limit to 100 km/h.

The motorway winds relatively steeply down past the Burnside Freezing Works, and crosses the Main South Road/Kaikorai Valley Road interchange on a single overbridge.

Once on the flat of the Kaikorai Valley the motorway passes underneath the northbound on-ramp from Green Island before passing between the suburbs of Green Island and Abbotsford to the Green Island/Sunnyvale interchange.

Beyond this interchange the motorway crosses the Kaikorai Estuary and bisects the suburb of Fairfield. There is a half diamond interchange at Old Brighton Road (northbound on, southbound off) before motorway climbs towards the crest of Saddle Hill where there is another half-diamond interchange (northbound off, southbound on) and a separate overbridge for Morris Road.

The motorway then descends from the slopes of Saddle Hill onto the floodplain of the Taieri River at Mosgiel. There is a full diamond interchange with SH 87, which is the primary access to Mosgiel from SH1. At this point the motorway narrows to a two-lane undivided road. The motorway designation continues for a further 600 metres before reverting back to an ordinary State Highway and continuing through the suburb of East Taieri.

[edit] History

A motorway extending south from the Andersons Bay intersection was first proposed from the late 1950s, when Dunedin, like other major centres in New Zealand, was experiencing rapid vehicle growth and a decline in public transport usage.

A report from De Leuw Cather was commissioned by the Dunedin City Council in 1963, which recommended a number of changes, primarily to Dunedin's arterial road system. A number of roads around the city were widened to accommodate four traffic lanes, and the report recommended that investigation, design, and construction begin of the proposed southern motorway.

During this time period the then Ministry of Works designated a substantial amount of land for future upgrade works along State Highway One, with a view that by the late 1990s, much of SH1 in New Zealand would be rebuilt as motorway, possibly along the lines of a US Interstate, with bypasses of all small towns, grade separation of all intersections, and no private property accesses. Within the Dunedin area, Council planning maps from the 1960s and 1970s show a designation for a "Dunedin to Milton Motorway" which is part of these Ministry of Works designations.

The present constructed motorway generally follows along the route of this early designation. Further evidence of the Ministry of Works intentions can be seen on the "Floodfree" section of SH1 near Henley on the Taieri Plains, 35km south of Dunedin, where the present two-lane road has been constructed with a 2.5 metre wide shoulder on the left (northbound) side, with a standard 0.5 metre wide shoulder on the right. This two lane road was constructed in the early 1970s as the north bound lanes of a motorway, with the intention that separate southbound lanes would be constructed in the future.

[edit] Section-by-section construction

The Dunedin Southern Motorway snakes its way south past Burnside and Green Island.

The present motorway has been constructed in a number of sections.

The first section was completed in 1972 and bypassed the suburb of Green Island.This section began at the southern end of Kaikorai Valley Road at Burnside, and travelled south for 2.5 kilometres, dividing Green Island from the suburb of Abbotsford. It ended at the southern end of Green Island, and connected with the main south road through the suburb of Fairfield. Construction of this section of motorway is considered by some people to have been a causal factor of the Abbotsford Landslide in 1979. Around the same time, construction began on the section traversing Saddle Hill, from Mosgiel to Fairfield. Earthworks were undertaken to allow for the construction of a four lane motorway, as well as northbound and southbound slip lanes extending from a future interchange with SH87 at Mosgiel. At the time, however, SH1 was constructed with two lanes and a northbound passing lane extending northward from the SH1/SH87 intersection.

The second section was a short 700 metre section of four lane dual carriageway completed in 1978. It extended southwards from the Anderson's Bay intersection, across King Edward Street on twin overbridges to connect with South Road near the Glen.

The 1980s saw the extension of the motorway south from the Glen to Barnes Drive, bypassing Caversham. Due to funding constraints at the time, this section was only built as a non divided two lane carriageway, albeit with no intersections.

SH1 from Barnes Drive to Lookout Point was upgraded with the inclusion of a second northbound lane, giving four lanes in total. Aberfeldy Street was limited to a left in/left out only intersection.

In 1987, due to high accident and congestion problems the at-grade intersection with SH87 at Mosgiel was upgraded into a full diamond interchange. Under severe funding constraints of this period, the SH87 overbridge was only built to accommodate two lanes of SH1 travelling underneath, which will make any future widening of SH1 at this point more costly.

In 1989-1990 the Green Island motorway was extended northwards up Calton Hill past the Burnside Freezing Works to re-connect with SH1 at Lookout Point.

A major extension was completed in 2003, when the 4.5km Fairfield Bypass was opened. This connected the southern terminus of the Green Island Motorway with the northern end of the Saddle Hill section of SH1. There were several delays in construction of this stretch due to the presence of mine workings that created major difficulties in the stabilisation of the land along the route. The Saddle Hill section was upgraded at this time as well to a full four lane divided motorway to take advantage of the preparatory earthworks completed in the 1960s.

The completion of the Fairfield section meant that SH1 was a now an uninterrupted 4 lane divided motorway from Lookout Point to the SH87 interchange.

[edit] See also

• List of motorways in New Zealand