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Keith Rankin: Motorway Choices

Motorway Choices

by Keith Rankin
14 December 2005

At long last the penultimate (Mt Roskill) leg of Auckland's southwestern motorway is underway. And the planning for the final (Avondale/Rosebank or Waterview) leg has intensified, with a view to completion well before the 2020 date that looked likely while John Banks was mayor.

Sadly, Auckland will become entrapped in the same kind of problem that has plagued Wellington. In each case there are two routes, where one route has double the benefits but also costs about 30% more. As we have come to expect, the councils that decide these things are biased in favour of the cheaper route.

There is no point in undergoing any construction process if it doesn't have benefits. The benefits are the projects' raison d'etre. So it needs to be with a clear focus on the benefits that the decisions are taken. Costs can be managed. They alone should not determine which choice is made.

In Wellington's case the choice for SH1 is between widening the inland coastal route, and constructing a new inland route through Transmission Gully. Really, when the benefits and social/environmental costs are considered, it's a no brainer. The more expensive (in accounting cost terms if not in economic cost terms) Transmission Gully wins hands down.

All that is required is a 2.5 lane highway from Haywards to McKays Crossing north of Paekakariki. (A 2.5 lane highway means two lanes with many passing lanes, especially on the steeper sections.) Transmission Gully could be like a mini version of the steep 2.5 lane Napier-Taupo highway. Extensions could be saved for later. The main benefits are to create extra road capacity into and out of Wellington, and to have an alternative to the precarious coastal route.

The Auckland southwestern motorway (SH20) has two main purposes and one secondary purpose. The first main purpose is to provide access from South Auckland (and south of Auckland) to Waitakere City and Auckland's northwest. It's second purpose is to provide (in conjunction with the nearly complete SH18 motorway) an alternative (by-pass) route north to the "Spaghetti Junction / Harbour Bridge" route. So it has important strategic objectives.

The secondary purpose is to provide alternative access to Auckland Airport for people who live within 5km north or west of the central city.

For SH20, the main environmental issue is Oakley Creek, with its lovely waterfall at the back of Unitec. Alongside the lower reaches is Great North Road, a four-lane road used by a large proportion of commuters from Auckland's southwestern suburbs (eg New Lynn, Titirangi). On the other side of Great North Road is the suburb of Waterview.

The route favoured by the planners (ie by the same types who in Wellington favour the coastal highway) is to run the motorway parallel to Great North Road and Oakley Creek.

Imagine a Pythagorean triangle, with sides of 3km, 4km, and 5km (see www.nzherald.co.nz/section/media.cfm?c_id=1&objectid=10359722). If the Oakley Creek route is followed, then traffic using the SH20 motorway for the primary purposes for which the road must be completed will be forced to follow the 3km and the 4km links. The alternative (sensible) solution is to build along the 5km "hypotenuse" link (Avondale/Rosebank), which takes this traffic directly where it wants to go.

Hence the Rosebank Peninsular route can be called the direct route, and the indirect Waterview route is the triangular or dog-leg route.

If the triangular route is adopted, then bypass traffic will be forced to mix with the commuter traffic that uses Great North Road, creating an enormous bottleneck. That would eventually have to be fixed by widening. And that later widening of the "dog-leg" will probably require the destruction of Oakley Creek.

Further, if the triangular route is adopted, it will place a further bottleneck on the present northwestern motorway (SH16); in particular the long estuary leg between Pt. Chevalier and Te Atatu. That leg is already the main bottleneck in the evening rush hour.

The only benefit of the Waterview (dog-leg) Route is that it will give residents of Grey Lynn, Herne Bay, Northcote and Takapuna an alternative airport access route. My feeling is that people living in these suburbs close to the city centre are over-represented among the people who will make the decision, whereas people in Waitakere City, South Auckland and Rodney District (who most need the motorway) and Waterview will be under-represented when the decision is taken.

We have seen what happens in Wellington when the city planners make a short-sighted decision that may work for inner-city residents but will not work well for anyone else. We also know what happened in Auckland when the Harbour Bridge was built too narrow in 1959. It soon (ie in the 1960s) became an unacceptable bottleneck that required "clip-on" lanes.

A decision to build the Waterview dog-leg instead of the Rosebank Peninsula direct route will sooner or later destroy Oakley Creek. The bottleneck that will be created in Waterview will, soon enough, require a fix. That fix will destroy Oakley Creek, even if the initial implementation of the dog-leg does not.

Finally, I would like to see the Green Party come to the party. We know that Green activists are generally opposed to motorways. But when the choice is not "whether to have a motorway", but "which route", it is the responsibility for our environmental watch-dogs to become engaged. The environmental damage that will eventually take place in both Auckland and Wellington - given that the myopic choices are the favoured choices in both cities - can probably only be prevented if green-minded politicians and activists accept that these roads will be built and focus on the "which route" debate.

*************

Keith Rankin - http://keithrankin.co.nz/

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