About this project

Background

Transmission Gully is so named because it generally follows the route of the Bunnythorpe to Haywards 110kV-transmission lines.

The desire for an inland alternative route for State Highway 1 (SH1) to bypass the coastal areas north of Wellington has been sought for more than 50 years and its main aim is to provide an essential alternative route out of Wellington.

Wellington Western Transport Corridor

There has been discussion for many years on building an alternative highway to the coastal route (State Highway 1) which is narrow in places and becomes congested during peak hours. An alignment for the Gully route was originally designed in 1996 and land was designated in local plans in 2004.

In 2004/5 as part of a statutory requirement to update its Regional Land Transport Strategy, Greater Wellington Regional Council (GWRC) jointly with Transit New Zealand (Transit) undertook and consulted on a transportation study of the Wellington Western Corridor. A Western Corridor Plan was developed from that study.

The Western Corridor plan recommended a number of solutions to address constraints to movement in the corridor. In terms of implementation, it recommended upgrading public transport along the corridor, with rail improvements being the number one priority. While commuters in the Region already show strong usage of public transport, and will be encouraged further; the sub-committee appointed to hear public submissions on the Western Corridor Plan, stated that upgrading public transport alone would not replace the need for substantial upgrade of the roading infrastructure in the Western Corridor.

The sub-committee concluded that the reality is that affected communities and other submitters wanted Transmission Gully and wanted the current Coastal Route to be effectively a combination of a local road serving coastal communities and those wishing to use the coastal amenities of the Region. Under that scenario, the Coastal Route could effectively become a scenic route along which lower speeds and volumes will prevail. Transmission Gully would provide for those interested in fast highway and freight movement.

Community feedback in 2005 favoured Transmission Gully and it was included in Greater Wellington Regional Council's Western Corridor Plan in 2006.

For more information on the approved Western Corridor Plan included in the Wellington Regional Land Transport Strategy click here

How would travellers benefit?

Compared to the coastal highway, the preferred Transmission Gully route would provide:

A safer road: four-lane route with central median barrier
Less likelihood of landslides, floods and road rupturing from a major storm or earthquake.
Peak period travel time savings estimated at around 10 minutes per vehicle for Kapiti to/from Wellington, 15 minutes Kapiti to/from Hutt, five to seven minutes Porirua to/from Hutt Valley
Shorter and more efficient route for freight movements to and from Seaview/Gracefield, Wingate and Wairarapa
Easier access from State Highway 1 to Porirua and Hutt Valley
Important arterial route for residential and light commercial areas east of State Highway 1 in Porirua

Why the preferred route?

Work undertaken on Transmission Gully since 2006 provided the first real opportunity to conduct on-site, in-depth investigations into the impact of the designated alignment on ground and environmental conditions. Limited knowledge of these effects was available when the alignment was first designed in 1996.

The preferred route follows the established Transmission Gully corridor but departs from the designated alignment along some of its length.

For a map showing the entire route and the existing "In-Designation" and "Preferred Alignment" click here

The preferred route provides several significant benefits, in addition to the identified cost savings. They include:

Environmental improvements

The preferred route will largely avoid native forests and will have fewer and shorter stream crossings. This will minimise effects on aquatic life, freshwater and marine ecosystems. It will also fit better within the natural land form than the designated route and will be less noisy for nearby residents or those using recreational areas.

Improved route security

The preferred route crosses the Ohariu Fault on an earth embankment compared to the viaduct proposed for the 2004 route. The embankment will be more resilient in a major earthquake and be easier and quicker to repair.

The preferred route cuts less into the hills and follows flatter slopes to reduce the risk of landslides.

Improved highway safety and function

The preferred route better suits the proposed 100km/h speed limit. It provides a median barrier along the entire route, crawler lanes on the steepest sections and auxiliary lanes for vehicles merging between interchanges.

Improved connections to local roads

An eastern Porirua interchange will connect to both James Cook Drive in Whitby and Warspite Avenue in Waitangirua, providing improved connections with the wider eastern Porirua area.

Opportunity to protect the environment

The preferred Transmission Gully route allows a better opportunity to enhance the environment and preserve people's enjoyment of their properties and recreational areas.

Planting is well underway in a number of areas with native trees and shrubs. More than 150,000 have been planted with many now well established. Additional planting is planned and this will allow easier passage for birds within the area.

The preferred route allows an opportunity to avoid adverse effects on aquatic life. It will have fewer stream crossings and will generally cut less into the hills, making it easier and simpler to treat run-off and stormwater along the route. Measures to control run-off will include the capture of sediment during construction and enhancements to the stormwater management system. Provision will be made for fish passage and natural debris flows in streams.

Work on environmental effects completed for the designated alignment identified the need for protection of several terrestrial, freshwater and marine environments.This work has continued and has included a detailed physical survey of the Te Puka and Horokiri Streams and Duck Creek.

Other specific social and environmental investigations included:

Noise monitoring to determine measures to reduce project and traffic noise
Visual and social effects considered to enable landscaping which would be sensitive to existing landforms and which would minimise the visual impact of the highway
Assessment of stormwater management requirements.
Archaeological investigations were undertaken in three areas most likely to have historic sites. No archaeological discoveries were made along the route.

Further detailed investigation work will be conducted and the team will be working with local environmental and community groups to ensure the best possible outcomes are delivered.

Reducing the impact of fault lines

Both the State Highway 1 coastal route and the Transmission Gully route cross fault lines, as is the case with many roads in New Zealand.

The preferred Transmission Gully route offers improved security for the region's road network over the existing coastal route even though it crosses two fault lines.

The preferred route crosses the Ohariu Fault on an earth embankment which will be more resilient in a major earthquake and allow easier and quicker reinstatement than the previously planned viaduct.

Reducing the impact of storms

The preferred route generally runs lower along the Gully to reduce the height and number of large cuts into the hillside, meaning the risk of a landslide is reduced.

Fewer bridges and culverts along the preferred route mean that there will be less obstruction to the natural movement of debris in streams during storms. This means that the overall risk of storm damage to structures as a result of debris build-up or washouts is reduced.

Regional Parks near the preferred route

The preferred route largely avoids native forest areas.
Sensitive landscaping appropriate to land form will minimise the visual impact of the road.
Bridges, viaducts and retaining walls will blend in with their locations.
Appropriate route design and landscaping will reduce noise levels.

Battle Hill Farm Forest Park

Battle Hill Farm Forest Park is an important regional recreational park owned by Greater Wellington Regional Council. It is also the site of the last battle in the region between Maori and the Crown in 1846. It is widely used for walking, horse riding, equestrian events, mountain biking, camping and picnicking. It also includes a commercial farm operation.

The designated Transmission Gully alignment crossed the park at a height of about 20 - 30 metres above the Horokiri Valley floor. It would cut across the ends of several ridges and relatively steep greywacke slopes that are currently covered in pine forest. It would also have cut across the eastern tributaries of the Horokiri Stream that are important fish habitats.

Sketch of Battle Hill Cross-Section

The preferred route reduces earthworks and crosses the park on flatter land on the valley floor close in against the low rounded hills known as Gas Line Ridge. The ecological and environmental benefits include:

Less risk of sediment entering Horokiri Stream
Less risk of sediment affecting Pauatahanui Inlet
Reduced intrusion of the highway on people's view and on the landscape
Reduced direct noise effects
Fewer structures such as viaducts.

Both the designated alignment and preferred route are located well away from the colonial homestead, cottage, woolshed, stockyards and gravestones, and the site of the battle itself on the ridge leading up to Battle Hill summit. The preferred route will continue to allow full recreational access to the park. A bridge will be provided across the highway to the rear of the park so that park activities can continue largely as before.

As Battle Hill Farm Forest Park is an important regional recreational park we welcome feedback from all park users. Follow these links to view the brochure and feedback form.

The preferred Transmission Gully Route

Heading south on State Highway 1, the preferred Transmission Gully route starts just south of MacKays Crossing, curving left up the Te Puka Stream valley and over the Wainui Saddle. It follows Horokiri Stream down to Battle Hill Farm Forest Park and on past Pauatahanui Golf Course.

The route swings west to cross over State Highway 58 about 600 metres southeast of the existing Pauatahanui roundabout. It climbs to the headwaters of Duck Creek, runs above the creek, and crosses Cannons Creek near the Takapu Road electricity sub-station.

The route follows the hills above Ranui Heights before dropping down through plantation forest opposite Kenepuru Hospital to join State Highway 1 at Linden.

For a map showing the entire route and the existing "In-Designation" and "Preferred Alignment" click here

In more detail the preferred route is as follows:

State Highway 1 MacKays Crossing/Paekakariki Interchange

The route to Transmission Gully from the north will cross above State Highway 1 south of MacKays Crossing. Traffic from Kapiti will still be able to access the existing State Highway 1. Traffic from Paekakariki township can access Transmission Gully via MacKays Crossing.

The preferred route no longer crosses the softer ground near the railway line and has less impact on adjacent productive land.

For a plan showing the preferred connection at MacKays Crossing click here

Te Puka Stream/Climb to Wainui Saddle

The number of stream crossings over an important aquatic habitat has been reduced in the preferred route.

Crawler lanes for the steepest section of the route on the climb and descent between MacKays Crossing to Wainui Saddle are proposed to take into account the large difference in speeds between cars and trucks.

For a plan showing the preferred alignment up Te Puka Stream to Wainui saddle click here

Battle Hill Farm Forest Park

The preferred route through Battle Hill Farm Forest Park is on the valley floor, instead of being high on the steep, wooded face of the ridges as in the designated alignment. The new route offers more opportunity to provide stormwater control and creates less risk of sediment entering the Horokiri Stream during construction. Its valley placement makes it less visible from the park and surrounding areas and reduces the level of road noise.

Click here for details on how the preferred route provides better opportunities to protect the environment

For a plan showing the preferred alignment through Battle Hill Farm Forest Park click here

State Highway 58 Pauatahanui Interchange

The Transmission Gully route will cross above the existing State Highway 58 route. There will be on and off ramps from Transmission Gully to a new two-lane roundabout on State Highway 58.

For a plan showing the preferred connection at State Highway 58 Pauatahanui click here

Combined Whitby/Waitangirua Interchange

The preferred Transmission Gully route runs under the proposed interchange. The roundabout links both James Cook Drive and Warspite Avenue at Waitangirua. There are no connections proposed to local roads on the eastern side of the route in line with Porirua City Council land use development policies.

Extra lanes on Transmission Gully will assist merging between State Highway 58 and the combined Whitby/Waitangirua Interchange. This combined interchange eliminates the need for the originally proposed Warspite Interchange by providing a more efficient link to both suburbs.

For a plan showing the preferred connection at the combined Whitby/Waitangirua Interchange click here

Kenepuru Interchange and Link Road

The Transmission Gully route will cross above a roundabout with on and off ramps, and a connecting road to Porirua. Extra lanes will assist merging where appropriate.

Porirua will be connected to Transmission Gully via a new 50km/h road over the existing State Highway 1 motorway and railway line to a new roundabout on Kenepuru Drive.

State Highway 1 Linden Connection

The Transmission Gully route merges with State Highway 1 using a Y-junction. Travelling south, Transmission Gully joins State Highway 1 as it crosses Collins Avenue bridge and along the Tawa College straight.

Travelling north, the Porirua motorway and Transmission Gully separate at Linden with two lanes diverging to the right to travel north along the Transmission Gully route. Two lanes diverge left to continue along the existing State Highway 1 to Porirua.

For a plan showing the preferred connection at Linden click here

How does the preferred route differ from the designated alignment?

South of Wainui Saddle, rather than being on the steeper, wooded eastern slopes, the preferred route crosses the gentler and less environmentally sensitive terrain on the western side of Horokiri Valley. Through Battle Hill Farm Forest Park, the preferred route is on the valley floor instead of being high up on the steep, wooded face of the ridges.

The remainder of the route is mainly unchanged except that, instead of an interchange opposite Takapu Road electricity sub-station connecting to Warspite Avenue, a single interchange is proposed at Whitby. This provides local road links to both Whitby via James Cook Drive and to Waitangirua, close to the shopping centre.

By eliminating the need for the Warspite Avenue connection at Cannons Creek, an improved alignment can be chosen, resulting in shorter bridge structures and reduced impact on Belmont Regional Park and Cannons Creek Reserve.

Property matters

Transit is contacting landowners directly to talk to them about the possible impact the preferred route might have on their properties. This builds on the contacts that have already taken place during the investigative phase of the Transmission Gully project.

A number of existing properties, rights-of-way and accesses would be affected by the designated Transmission Gully alignment. This is also the case with the preferred route.

In some cases, landowners affected by the designated alignment will no longer be affected by the preferred route. There will also be landowners whose properties were previously untouched but who will now be affected by the preferred route.

Where the Government is acquiring any property for a public work, it is a basic principle of compensation that an owner shall be entitled to fair and reasonable compensation for the losses that may occur. When acquiring land from an owner, Transit engages an independent Land Information NZ accredited agent to be sure the compensation process is transparent and fair.

Transit is working with all those whose properties are potentially affected by the route.

All Transmission Gully Project property issues are being managed in compliance with the Land Information NZ guidelines for acquiring property under the Public Works Act 1981.

To view a copy of the Land Information NZ guidelines click here

For any enquiries regarding property issues related to the Transmission Gully Project, please call 0800 TG INFO (0800 844 636)