SH2 Rimutaka Realignment Hero

SH2 Rimutaka Realignment: making a precarious stretch of road safer.

State Highway 2 is New Zealand’s second longest highway, connecting the outskirts of Wellington and Auckland via Tauranga. Muldoons Corner (named after a tight-and-to-the-right Muldoon budget), in the Rimutaka Ranges, was the sharpest and tightest corner on the hill road between Wellington and the Wairarapa.

Approximately 5,300 vehicles used this stretch of road daily. The NZ Transport Agency wished to make this notorious corner safer. Hawkins and Opus International were engaged to complete the NZ$13.9M realignment.

NZ Transport Agency’s aim:

  • To make the route safer and easier for motorists to navigate by straightening it.

What we did:

We worked together with Opus International to complete this 1 kilometre realignment.

The project involved constructing new , and widening the existing, roadway. This included installing large waterway culverts, and the mitigation and re-vegetation of the native plant species. Earthworks made up a large component of the project, with 231,000m3 of rock excavated along the one kilometre road length.

The extensive earthworks were undertaken in a difficult environment with very high, steep hills and very deep, steep gullies. The highest cut on the project was 55 metres above the road. The safety of operations was closely monitored to ensure public and road safety at all times.

It was imperative that the road remained operational at all times as it is a critical lifeline between the Wairarapa and Wellington, providing access to regional facilities such as the port, airport and hospital. As a result, traffic management was an integral part of site safety. This was managed in a way that resulted in minimum delays for motorists. Large construction trucks and vehicles had to cross the state highway to access the cut and fill sites. Any work requiring traffic to be controlled was carried out off-peak via manual stop/go signs and temporary traffic signals.

Unique challenges:

Environmental management was a key issue. We couldn’t carry out any earthworks that would affect the waterways between 1 May and 31 August each year as this could disturb the fish spawning. Because the project site is prone to large volumes of rainfall, environmental controls were put in place to protect the surrounding streams from sediment and mud that runs off the site. This involved establishing holding ponds to allow sediment to settle and the clean water to then flow into the stormwater drains.

Three large concrete culverts were installed to carry water under the new road and down to the bottom of the gullies. Dissipators were required at culvert outlets to reduce the velocity of the water and discharge it into the existing watercourses in a controlled manner. Provision for fish passage in some of the larger culverts was created by epoxying small concrete blocks to the bottom of the culvert invert. This allows fish to rest as they would in a natural stream bed.

The mitigation and re-vegetation of native plant species was important. Important specimens were identified prior to construction and protected on site, or relocated temporarily during the construction phase. A total of 38,000 plants were planted following construction. Due to the steep terrain some landscape work had to be completed by specialist abseilers. The plants were all grown from locally sourced seed as per the resource consent requirements.

The outcome:

Officially opened on May 12 2012, the 5,300 daily road users are experiencing significant safety benefits from the new straightened road alignment, improved visibility and better edge protection from the steep drop into the valley.

 

After two and a half years of battling searing heat, horizontal rain, snow and 150kmh gales, we've got a safer, easier route for thousands of motorists to negotiate every day, and that's a tremendous achievement… This has been one of the most challenging work sites in the country, and I take my hat off to the team, who have done a splendid job in bringing in this project on time and within budget.

Rod James

NZTA State Highway Manager