Since 2007 11 deaths and 45 serious injuries have occurred on a section of SH3, making it a high priority for improvement. Richard Silcock checks out the current work and reports on the plans for constructing two bypasses.
IMPROVEMENT PLANS for the 58-kilometre, Mt Messenger to Awakino Gorge section of SH3 on the north-western flanks of Taranaki have been ongoing for some time. Due in part to the poor alignment, loss of vehicle control by drivers and driver inattention, this section of highway has been the scene of a number of road fatalities and serious injuries.
The highway has also suffered road closures due to rock falls and the instability of the ground. The detour route adds four hours to the trip so the planned improvements have been welcomed by regular users of the highway.
Plans for two bypasses, a tunnel and several new bridges were announced by the Transport Agency at the end of August last year and will form the most significant part of an overall improvement programme.
A lot of safety work involving the widening of the road and the removal of some treacherous bends is already well advanced. The stage has now been set for the construction of the two bypasses – one at Mt Messenger and the other at the Awakino Gorge.
At Mt Messenger a six-kilometre bypass is planned to run east of the existing highway and will include a 125-metre bridge over an important wetland area and a 235-metre-long tunnel south-east of the present highway.
Other work includes bypassing the single-lane Awakino tunnel (which opened 1923) and the construction of two new bridges over the Awakino River.
These construction features along with extensive improvement work will form a part of making the highway a much safer stretch of road for motorists.
These improvements include widening the road, the adding of road-level side barriers to prevent vehicles running off the road (5000 metres of safety barrier have already been erected), removing trees to improve sight lines, providing more and improved signage and creating ‘pull-over’ rest and passing areas particularly in the gorge itself.
Electronic warning signs have already been installed at high risk spots, with the area south of Mokau, which is particularly risky, given special attention. The signs are activated by moving traffic and have been proven to be more effective at alerting drivers to approaching hazards than the more traditional static signs. Passing lanes at the western end of the Awakino Gorge and north of Tongaporutu are also to be added to increase safety for passing slow traffic.
This improvement work is being carried out by Downer Construction, HEB Construction and Beca as design consultants.
The Transport Agency’s director for regional relationships for the central North Island, Parekawhia McLean, says the proposed bypasses are the optimal solution for this section of the highway.
“It [the new section] will greatly improve safety and help to better connect the Taranaki region with the King Country and southern Waikato,” she says.
An Alliance has been formed to carry out the feasibility, design and construction work for the Mt Messenger section. It comprises NZTA, Downer Construction, HEB Construction, Tonkin & Taylor, WSP Opus, Holmes Consulting and Isthmus.
Five options were investigated and assessed during the feasibility study phase, with the route chosen providing the best solution.
Geotechnical engineers carried out extensive ground tests involving the drilling of 35 boreholes which are 85mm in diameter and up to 100-metres deep and carried out 70 penetrometer tests. They also excavated a number of ‘wells’ and measured groundwater levels.
Alliance project manager (Downer) Duncan Kenderdine says this investigative work was an exercise in logistics given the steep, largely inaccessible terrain.
“The team had to carry their heavy and bulky testing equipment to many locations and we had helicopters deliver the drill rigs to the more remote areas,” he told Contractor.
“It [the new section] will greatly improve safety and help to
better connect the Taranaki region with the King Country
and southern Waikato.”
“While the terrain is very challenging and in some of the hilliest and most densely vegetated parts of the North Island, we will be taking into account the environmental and cultural considerations during the design and construction phases of the project, with strict protocols to protect the environment,” he says.
The environmental manager, Tonkin & Taylor’, Brett Ogilvie, says that while they have been very mindful of the ecological values associated with the area, they have also been looking at ways to restore and improve the environment.
“The team has carried out investigations for a variety of wildlife and plants, with comprehensive surveys of the vegetation, the numerous streams and wetlands and has helped develop solutions that respect the environment,” says Brett. “For example, the intended alignment will avoid the kahikatea swamp to the south of Mt Messenger.”
Current proposals for mitigation measures to restore and even improve the ecology include nine kilometres of stream-bank planting, the replanting of nine hectares of vegetation, creating six hectares of swamp-forest habitat and controlling pests in 560 hectares of native forest.
“The new alignment will be more resilient than the existing route and the other options we looked at because it will avoid large areas of very unstable land,” says Parekawhia.
“It will also be of a far lesser gradient than the existing route, allow for faster travel times [the route will be almost one-kilometre shorter than the existing route] and provide significant benefits for heavy vehicles.
“Utilising bridges and a tunnel in the design will significantly reduce the road’s impact on the ecological values and the native bush,” she says.
“The proposed alignment may affect some conservation and Maori-owned land containing native vegetation, however these areas have seen considerable damage caused by pests and we see some significant opportunities for improving the area in this regard as well.”
The current road widening work part of the project is expected to be completed this month, with work on the bypasses expected to start in the latter part of this year for completion by mid-2020*.
The overall cost is expected to be in the region of $200 million.