Building barriers

After nearly 20 years of faithful service, the Auckland Harbour Bridge’s moveable lane barrier system has finally been replaced with the latest model transfer machines and a new, slimline barrier.   MARY  SEARLE was there to watch the transformation.

Barrier_3.jpgLove it or hate it, Auckland is our largest city, home to nearly a third of the entire country’s population. It’s a sprawling metropolis; its 1.3 million people spread over 637 square kilometres of city, suburbs and islands.

The Auckland Harbour Bridge, which celebrates its fiftieth birthday this month, is a vital link in the city’s roading network. Each day more than 170,000 vehicles use it, a far cry from the paltry 8250 vehicles it was originally designed for.

Within 10 years of it being built the bridge was widened from its original four lanes to eight with the addition of box girders on either side of the bridge with two lanes on each, supported on the original bridge piers by independent superstructure. And still traffic volumes grew.

During peak hour, a large percentage of this traffic is commuters, heading south in the morning into the city and home again to the North Shore suburbs in the evening.

Barrier_4.jpgThis tidal flow of traffic puts great demands on the eight-lane bridge, so overhead lane signals and a moveable lane barrier work to increase capacity. Each day, the southern transfer machine moves north, moving the barrier from right to left to create three lanes north and five lanes south for the morning commute into the city. Once rush hour has passed, it heads south again, moving the barrier back to the centre, allowing four lanes of traffic in each direction. As the evening rush approaches the northern barrier machine creates five lanes north and three south, restoring it to four and four later in the evening.

The barrier was first installed in 1990 to prevent cross-centreline head-on collisions. In the five years to 1988 there had been ten fatalities between vehicles travelling in opposite directions on the bridge, and in 1989 alone another five people lost their lives in head-on crashes.

The moveable lane barrier eliminated cross-centre line incidents altogether, with not a single cross-median fatality recorded since its installation. This in itself is makes the barrier a resounding success, however vehicle numbers in the centre lanes have also increased as travellers felt more comfortable using them with the accident risk substantially reduced, and consequently the bridge’s overall capacity rose.

Nearly twenty years on, the Auckland Harbour Bridge moveable lane barrier continues to work well and has become the longest serving, permanent use, moveable lane barrier in the world. However, after two decades service, the transfer machines had long past their life expectancy and they and the barrier itself were replaced in late-February.

Barrier_1.jpgAs the Auckland Harbour Bridge is such a critical piece of the city’s infrastructure, the barrier replacement had to be done with as little impact on the travelling public as possible, i.e. in the middle of the night over a weekend.

The project was spread over two nights in several stages, the first being to install the new barrier, the second to remove the old. The whole job needed to be completed by 4.30 on the Monday morning in time to move the new barrier into place for the peak hour commuter traffic.

This was no simple task. The new barrier comprises 2000 sections (comprising two of the concrete barriers linked together) and 60 variable length steel sections. The project required eight forklifts, 16 trucks, numerous traffic control vehicles to manage the lane closures on the approaches to the bridge, and two teams of men putting in the pins that link the sections together. A total of 50 people were on the bridge for the project – from truck and forklift drivers and the men connecting the barrier pieces, to the traffic control team, the police, staff from bridge owners the New Zealand Transport Agency (NZTA) and its consultants, Resolve Group, and experts from manufacturer Barrier Systems Inc.

Barrier_6.jpgPlanning for the replacement of the barrier began months in advance. The concrete sections were manufactured in Hamilton and stored on site in November 2008. Excitement rose with the arrival on February 7 of the ship carrying the new barrier transfer machines. Two days later they were trucked to site, given their new livery of NZTA branding and the operators underwent  training to familiarise themselves with the new machines.

Things looked a little uncertain weatherwise in the lead up to the big event, with gale force winds and rain predicted for the weekend of February 28-March 1. Not that this would have affected the barrier installation itself, but high winds can play havoc with traffic control cones and that would have forced a postponement of the project. As it was, the storm blew through early and by the time Saturday evening approached, Auckland had returned to the muggy calm weather it usually experiences in late summer.

Things got underway with a safety briefing at 6pm and work started two hours later with the final move of the 19-year-old barrier by the old machines. Southbound traffic was restricted to the two outer clip-on lanes and northbound traffic restricted to three lanes.

Barrier_7.jpgIdeally the four central lanes of the bridge, separated from the clip-ons by the bridge’s superstructure, would have been closed to traffic for this operation, but the western box girders are currently undergoing strengthening work and, as a result, heavy vehicles are not permitted to use these clip-on lanes. So the workers were separated from the northbound traffic through the superstructure by the old moveable lane barrier.

The new 2.2 kilometre-long barrier string was placed by two teams that started in the middle; one moving north, the other south.

For ease of assembly the barrier sections were already pinned together in pairs. Each pair was loaded onto trucks by forklifts with a specially designed attachment that allowed them to easily pick them up and place them lengthwise. The sections were then transported the short distance from the on-site storage area at the northern end of the bridge to where the barrier string was being installed. There, another pair of forklifts unloaded the sections, carefully placing them end-to-end so the connecting pin could be positioned and then hydraulically driven into place.

Once each truck was unloaded it headed off to be reloaded, and so the process went all night.

Barrier_8.jpgBy 9am on Sunday morning the new barrier was installed and the bridge almost fully reopened to traffic – four lanes southbound were open and three northbound. The lane between the old barrier and the new was left unused for the day.

On Sunday evening, southbound traffic was restricted to the eastern clip-ons and the two new barrier transfer machines moved from north to south, one shifting the new barrier to the left and the other travelling in the closed central lanes to its new home on the south side of the bridge. This left the two southbound clip-ons for the travelling public and the far left lane of the central bridge (nearest the southbound clip-on) open for northbound heavy vehicles.

And so the process was repeated. Once again beginning in the middle, the team reversed its processes to dismantle the old barrier.

They had from 8pm until 4.30am to do this, when the new barrier was scheduled to be shifted across two lanes to open five lanes for the Monday morning southbound rush hour traffic.

Barrier_2.jpgThings went very smoothly throughout the project, especially when you consider that this is a once in twenty years job for the Auckland Harbour Bridge and, as a result, most of the people on the job hadn’t done this or anything like it before.

The men connecting the new barrier and dismantling the old were from the road maintenance crew at Fulton Hogan, which has the maintenance contract for the Auckland motorway network and who are far more familiar with paving works. So the first few hours of the job were a very steep learning curve, which they tackled admirably.

As the project was carried out overnight, the disruption to the public was minimal. A slight time overrun on Monday morning caused congestion problems up the Northern Motorway and not insignificant delays to commuters but all lanes were open by 7am and by 9.30am things were back to normal.  

Contractor, Auckland Harbour Bridge Special Supplement, May 2009
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