Unravelling that Spaghetti

By ARNOLD PICKMERE


Engineers are making extensive efforts to correct faults, shortcomings and safety worries in Auckland's Spaghetti Junction system.

Their main work is completing motorway-to-motorway connections in the area with all that entails. But an important part of the $195.35 million projects now in train has been to address existing problems.

Perhaps no better example exists than the familiar on-ramp to the Southern Motorway from Hobson St. One of the oldest on-ramps in the city, it is prone to slowing traffic to a walking pace at the slightest mishap, any hour of the day or night.

It is basically designed like an old-fashioned possum trap - the bait (motorway access) at one end of the box and a trapdoor that blocks escape once you are inside.

Motorists at the traffic lights at the top of Hobson St cannot see the state of congestion on the downward-sloping ramp and motorway until they advance across the intersection.

Once they have done that, there is no way of escape, nothing to do but to crawl forward in the queue. Possums caught in the headlights and Aucklanders caught in the brakelights have something in common.

The trouble is that a double lane on the ramp, intended to help keep the traffic intersection clear, becomes a single lane after about 50m. And a similar distance farther on this merging traffic has to contend with another merge with the heavy, often slow-moving traffic on the main motorway lanes coming from the Harbour Bridge. It is a recipe for frustration - and weaving drivers.

And for years it has seemed that the huge concrete Karangahape Rd retaining wall near the Hobson St on-ramp and motorway lanes in the area has denied a solution. But the private enterprise and Transit engineers who have been looking at such problems for several years now have a solution.

They intend moving the motorway lanes away from the wall and a little closer to a pillar on the other side (which will have to be specially protected). They will win just enough space for a merging lane on the left which will run all the way up to the area of the Symonds St on-ramp. This extra length should give motorists from the Hobson St on-ramp a much better chance to match the speed of the motorway traffic and merge more easily.

Engineers are winning such extra lane space wherever they can in the junction area.

Container trucks labouring uphill from Grafton Gully are getting another long, more level merging lane as they turn south on to the motorway towards the Newmarket Viaduct. It will give them space to get up speed before they merge.

Other examples of improvements include:

LEFT-HAND EXITS

The Nelson St off-ramps in the central city from the Southern and Northwestern Motorways both have right-hand exits from the motorway, which means motorists have to weave to the right-hand side often in heavy traffic.

In the case of traffic entering the Northwestern from Western Springs, for example, accessing the present Northwestern off-ramp to Nelson St means moving across four lanes of traffic. Such right-hand exits also affect flows on the main motorway lanes.

The solution will be much safer left-hand exits into new lanes to be built to Nelson St. For the Northwestern to Nelson route this means considerable redesign of present lanes.

The Southern to Nelson off-ramp will be a new lane on the west side of the motorway crossing over to Nelson St above the motorway. Both these lanes will be quite long. They will change from single to double lanes nearing Nelson St.

LONGER MERGING LANES

The present connection in the central motorway junction where traffic can turn from the Southern Motorway northbound into the Northwestern Motorway is to be changed.

The present bend is awkward, and westbound traffic from the Southern, Nelson St and the Port now has to merge from four lanes to three before the nearby Newton Rd on-ramp.

Planned improvements will enable four single lanes from the Northern Motorway (new link) Nelson St, Port and Southern Motorway to flow west on to the Northwestern in four lanes, eliminating the need to merge.

Improvements to the bottom of the Newton Rd on-ramp westbound will also extend the time for trafficto merge on that route.

Transit is also considering work to provide a fourth lane westbound on the Northwestern all the way between the Newton Rd on-ramp and the St Lukes Rd off-ramp at Western Springs.

The ingenuity and money ($195.35 million) being employed to make Auckland's central motorways function better and more safely promise significant improvements. But in some ways the efforts to gain extra lane space throughout the central system also illustrate the pressure. It is a matter of gains, rather than wins.

Wayne McDonald, regional manager for Transit in Auckland, has observed that simply building to beat Auckland traffic congestion is no longer an option. Future road projects and improvements have to also involve public transport solutions.

Traffic in the central motorway system at 200,000 vehicles a day is about three times heavier than it was 25 years ago. About 150,000 vehicles cross the Harbour Bridge daily, there are 113,000 on the Northwestern Motorway and 81,000 a day already using the Southwestern.


MOTORWAY MILESTONES

1940s: Auckland's main roads Great South Rd and Great North Rd unable to cope.

1953: Southern Motorway - first 3.2km motorway section Ellerslie to Mt Wellington opens.

1955: Northwestern Motorway - 7.8km from Great North Rd at Pt Chevalier to Lincoln Rd; Southern Motorway - 9.4km Mt Wellington to Wiri.

1959: Auckland Harbour Bridge opens. Northern Motorway progresses.

1960s: Central Motorway Junction designed for inner Auckland.

1970s: Most present links in Central Motorway Junction constructed this decade but junction never totally completed.

1971: Symonds St on-ramp opened in central city by Grafton Bridge.

1973. Southbound on-ramp to Southern Motorway at Hobson St.

1977: Southern Motorway exit to Nelson St.

1978: Link between Southern and Northern Motorways completed; on-ramp from Grafton Gully to Southern completed.

1988 Access from Northwestern Motorway to Grafton Gully.

1989. Northwestern to Southern Motorway link completed.

2004: Central Motorway Junction project stages one and two being built ($193.35 million). Completion June 2006.