$2 delight

On January 25 the country’s first electronic toll road opened, two months ahead of schedule, with the NZ Transport Agency recording almost 98,000 journeys on its 7.5 kilometre length during the first five days of operation.   BY MARY SEARLE

The original State Highway 1 route between Orewa and Puhoi contains winding, narrow sections of road and was not designed to carry heavy traffic volumes. Talk to anyone who’s travelled it and they’ll give you an equally long and winding story about being stuck for hours behind a truck or a campervan.

The new toll road, which is mostly four-lane, features clearer sight lines, smoother turns and reduced road gradients, making for a safer drive.  And commuters are already revelling in the reduced journey time – it seems $2 is a very reasonable price to pay for saving up to half-an-hour’s travel time.

However, the road to the Northern Gateway wasn’t completely straightforward. The haphazard geography of the site provided difficulties when building cuts and the location of the road, through beautiful native bush, posed environmental challenges.

But the end result produced by the Northern Gateway Alliance is pretty impressive.

One of the key features of the Northern Gateway is the Waiwera Viaduct – the country’s longest balanced cantilever bridge.

Sitting up to 31 metres above the tidal estuary, the Waiwera Viaduct is 537 metres long, with span lengths of 76 metres, and is built as two independent structures with a gap varying from 2.5 to 11 metres between them. The variable separation distance is needed to split the northbound and southbound lanes in preparation for entering the tunnels immediately north of the viaduct.

The bridge superstructure is a pre-stressed concrete box girder.  It was built using the pre-cast segmental balanced cantilever method of construction that utilises an overhead gantry. This method of construction allows the superstructure to be constructed without access from the ground, and this is important since some areas under the bridge are inaccessible for ecological and topographical reasons.

The Otanerua Viaduct is one of two eco-viaducts on the toll road which provides an ecological corridor under the motorway that enables wildlife to travel unimpeded throughout the bush. Sitting at 32 metres above the valley floor, the view from the Otanerua viaduct is on to the tops of the young forest canopy.

Rather than craning in the precast open top, super tee girders for the bridge and creating big platforms to do that, the contractors instead launched them off the top of the bridge and worked their way along.

Access to the valley floor to build the pier was a “bit of a goat track” and made little impact on the native bush. Some trees had to be removed to make way for piers, but otherwise the native bush was left untouched. This dedication by the contractors to environmental protection has been praised by the NZTA, and a great example of this was the modification of the launching truss that put the beams in place to avoid having to cut out extra trees.

The viaduct creates a bit of a rain shadow for the bush underneath it, so run off from the batter slopes on the cut is captured in a swale and collected in a tank and then used to water the shaded strip. The irrigation system is not a flash one, but it’s effective –pipes simply laid out on the ground which let the water seep out.

The earthworks

Bridges and viaducts aside, the earthworks part of the project was fairly large, with about four million cubic metres of dirt moved.

The cuts were fairly difficult to build thanks to the unusual geology, which comprised both gravel and clay, and there were real issues with water table levels – some of the cuts are still seeping and have drains in behind them to release pressure.

To preserve as much native bush as possible, the batters are as steep as they can be without creating a risk for the highway.

The biggest cut, which had 1.3 million cubic metres taken out, has a 40 degree batter without benches (to further reduce impact on the bush environment) and is about 55 metres deep from the top to the bottom of the cut.

It was decided to blast rather than dig the cuts out so the material would be broken up in to small pieces and easily transported down to the fill sites.

In the end there was more cut than fill. However, all material was disposed on within the boundaries of the job. And not all the cut was usable – a lot of it was over wet and unsuitable as fill – so was placed in a couple of disposal areas which are now planted over in native bush.

The tunnels

The Northern Gateway’s twin tunnels are 340 metres long and are pretty advanced for road tunnels in this country. 

They have lights that automatically adjust to suit driving conditions – when it’s bright outside the tunnel the lights are bright, when it’s gloomy or dark outside, the lights are dimmer so there’s less impact on motorists when driving in and out of the tunnels.

The tunnels also feature big fans situated throughout their length in case of an emergency involving fire and smoke filling them up. The fans will blow out the  smoke allowing people to get out of their vehicles and escape without suffering from smoke inhalation. The tunnels also feature footpaths down their sides and there’s escape passages providing access between each tunnel – which also gives access for emergency services.

Another key feature is the deluge system. Up above the tunnel on Fowlers Access Road there’s a tank that holds about 800,000 litres of water. In case of fire the sprinklers can be set off in the affected zone (each zone is 40 metres and there’s enough water to saturate a zone for 90 minutes). This is an automatic system that can also be manually overwritten by an operator.

The tunnels are monitored back at the Northcote Control Centre. A PA system allows controllers to talk to anyone in the tunnel if there’s an incident. If for some reason the operator is away from the desk when an incident occurs, the tunnel emergency system is capable of working automatically.

The tolling system

The big advantage of the electronic tolling system is that motorists don’t have to stop or slow down to pay the toll. When passing under the toll gantry, cameras record the vehicle’s number plate. Specialist software then matches the numberplate up to an account, if one is set up, or generates a payment notice.

Although motorists can pull up and pay at kiosks at either end of the road system, electronic payment is encouraged. It’s the fastest solution considering the biggest advantage of a toll road for users is a reduced travelling time. Travellers can buy credits in advance or have up to three days post-journey to pay, either online or by credit card over the phone.

The idea is for regular users of the road to establish prepaid accounts, topping them up as necessary. The NZ Transport Agency says over 11,000 accounts have already been set up and fewer people are using the kiosks to pay the toll.

Designed by Austrian-based Kapsch, the new tolling system is very advanced. The cameras capture both front and back number plates. And it doesn’t matter where on the road you are – changing lanes, hard up against the barrier or on the edge of the road, the cameras will see you. They will snap tailgaters too, as long as they’re more than a metre away from the car in front of and behind them. Speed is not an issue either, with tests showing plates recognised on vehicles travelling in excess of 160kph. The system can also capture license plates on motorcycles, although they can currently use the roadway toll free.

The system also measures the length of the vehicle to identify heavy vehicles, which have a higher toll.

Failure to pay the $2 toll for cars or $4 for heavy vehicles, results in a $40 fine.