Posted by: senjmito | November 6, 2011

Transmission Gully – knight in shining armour or Trojan horse?

I have a friend who lives at Paekakariki. When he bought his house it was a small, quiet seaside town. Now it is a small seaside town, but not quiet. The main road traffic roars past day and night, ruining his peace.

And there are many people in Pukerua Bay, Plimmerton, Mana, and Paremata telling the same story.

It is these people who have been pushing for the Transmission Gully Motorway (TGM) – the knight in shining armour that will rescue them from the traffic baddie. With TGM roads will once again be empty of traffic, there won’t be big trucks, local traffic will be able to easily move around, and people will stroll and cycle along pleasant roadways.

Another group of champions have been people concerned about Pauatahanui Estuary. Existing traffic along the roads next to the Estuary is producing contaminated stormwater that is adding to the problems for the Estuary.

Costs and Benefits

Is TGM worth the cost – $2 billion and damaged ecosystems – and will it really deliver? Or will it just create a whole new set of problems and become a Trojan horse?

According to NZTA’s data in its application, people at Paremata will get a reduction in traffic in 2026 from a projected level of 60,600 to 44,100 cars a day. That may make a slight difference to people trying to drive around the roundabout, but will probably not be noticeable to residents and pedestrians. If you currently cross the road by the railway overbridge, you’ll have to keep doing that.

And along the road south of the estuary it is similar: 16,800 only reduces to 12,600 – not really the answer to the stormwater pollution problem.

But things get better the further north you go. At Mana the reduction is from 35, 000 to 20,500. Probably not enough to make any difference to how the road works, but maybe a bit quieter at some times of the day. At Paekakariki the picture is much better – 22,900 becomes 3,100.

But even at 3100 cars per day, NZTA’s own guidelines say that unless you reduce the traffic speed to somewhere around 50km/hr you will still need separate cycle lanes – that’s just too much traffic for cyclists to be safe at open road speeds, never mind fun.

In addition, the reduction may not be the same for all types of vehicles. In the original designation hearing, NZTA’s expert said that only 30-40% of trucks would use Transmission Gully, because it was so steep and long. There’s no reason to think that the situation will be any different now. Truckies have always said they will go on using the coastal route. So the reduction of 86% near Paekakariki may be largely cars, leaving the truck volume still very high.

So why so little benefit for many of these communities, even using NZTA’s calculations which are likely to be optimistic?

One answer is the design of TGM. With so few entrances to the road, people who live in the more southern coastal communities and commute won’t be able to use it. So it is really only the commuters from north of Mackays who will bother.

The other problem is traffic induction. It is well recognised internationally that extra roads equals extra traffic. The assessment for NZTA found that this will apply to TGM as well. They found that there would be induced traffic, created partly by people doing more trips and partly by people moving off rail onto the roads. The extra road capacity is also likely to encourage people to travel at peak times rather than on the shoulders.

What Transmission Gully would do to the region’s transport systems

So what does that mean for the overall transport system? It means more traffic overall, a loss of income for the rail system and therefore less money to improve it, and a sharper peak.

All that extra traffic has to come from somewhere and go somewhere. TGM users aren’t travelling from one part of TGM to another part. So more traffic overall means more traffic and more congestion in Kapiti, in Ngauranga Gorge, in Wellington City. And that traffic will be more of a problem if it is concentrated in the peak. And the pressure will be on for yet more roads – Grenada Petone, a second Terrace Tunnel, the Kapiti Expressway. Stephen Joyce has said that TGM is needed to make the Kapiti Expressway work, and the Kapiti Expressway is needed to feed traffic into TGM.

If the ability to improve the rail system is lost, because all the money has been spent on roads and patronage has also reduced, there is a risk of our public transport systems entering a downward spiral of the sort we saw in the 1950s, with declining quality of service leading to declining patronage, leading to declining services… Which will be a problem for those using TGM who need the rail as an alternative, but a disaster for those who can’t – the increasing number of individuals and households that won’t be able to afford to commute by car as fuel prices rise, or that can’t get a drivers licence.

I suspect the knight’s armour is black– the colour of oil. The penguins in Tauranga would tell you that black isn’t always a flattering colour.

– Paula Warren

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