The business of the Basin Reserve flyover has been on my mind so I thought I’d use this guest post to question our current strategy for SH1 between The Terrace and Kilbernie. You see, the thing is I’ve just not been able to work out who is supposed to be happy with the current strategy. Of course we’ve got the motorists represented by NZTA (and half of the WCC) who want improved roads and reduced congestion. We’ve got the public transport advocates who argue we need to tackle congestion by getting more people out of cars and into improved public transport. And we have the residents, architects, and planners concerned about whether what we do damages or improves our urban environment. Only the motorists seem to be happy, but I don’t think they should be.
To recap the current strategy: it starts by grade separating east/west and north/south traffic at the Basin Reserve and widening the Inner City Bypass (ICB) to three travel lanes, continues with the duplication of the Mt Victoria Tunnel and widening of Ruahine St and Wellington Rd to four travel lanes, then concludes around 2026 with the duplication of the Terrace Tunnel. The strategy reaches a dead end at this point.
I can’t tell if this dead end is planned or not, since no one seems willing to acknowledge that there’s any problem with it. But I feel this end state is less than ideal for Wellington. From the motorists’ perspective we will clearly have a capacity imbalance across the different parts of the route, with duplicated Terrace and Mt Victoria Tunnels flowing onto congested surface streets. From the urbanists’ and residents’ perspective we’ve done serious damage to the Basin Reserve with the flyover and to Te Aro with the curvy ICB, and we’ve directed tonnes of traffic into our city (currently 60% of traffic on Vivian St and the ICB is through traffic that doesn’t belong in the city). The public transport advocates would argue that the money should be spent on long overdue public transport improvements before pouring it into new roads, but that aside, they surely can’t appreciate the suboptimal design that hinders the ability to create dedicated bus and light rail rights of way, and hinders closing Courtenay Place.
So once we reached this point, and everyone is hopefully thoroughly unhappy, if we wanted to increase capacity, or bury this traffic, what could we do?
At the Basin Reserve the only move we can make is to duplicate the flyover. We can’t change our mind in future and build a tunnel because the footprint of the tunnel and Basin Reserve flyover overlap, the level of disruption and cost would be too great to consider anything other than a duplicated flyover. These flyovers would then be directed into a new cut-and-cover tunnel constructed between the Terrace Tunnels and Basin Reserve to give us something resembling the following.
However, this will not be a very tenable proposition. Of course I doubt anyone in future will accept a duplicated flyover at the Basin Reserve. Beyond that it will mean demolishing and digging up the new Memorial Park, relocating the memorials. It will mean building the tunnel to the north of the ICB in order to avoid diverting over 20,000 vehicles per day off the ICB onto other routes such as the waterfront. This will require us to purchase a 30 meter wide swath of land, demolishing and relocating many buildings at great expense. Some of which have already been relocated during the construction of the ICB, many of which may be newly constructed in the intervening time. Many of these are significant buildings, including the dental school. These are the kinds of issues that held the ICB up for years, but on a grander scale. Here’s what a 30 meter wide swath of land means by the way.
As for cost, the current strategy, assuming we go with the lowest cost flyover option with no Memorial Park tunnel, comes to between $505-592 million before we’ve started digging a tunnel under Te Aro. That is $75-100 million for the Option A flyover followed by $430-492 million for the duplicated Mt Victoria Tunnel and widened Ruahine St and Wellington Rd. Now if we then decide we want the tunnel we would be facing an additional cost in the region of $730-760 million, bringing the total cost to reach the final goal to $1,235-1,352 million. This is composed of $90-120 million for the duplicated flyover to the north (taken from Option B’s cost) and $660 million for 1,100 metres of cut-and-cover tunnelling at a rate of $600 thousand per meter. I’ve excluded property costs because it would be too painstaking to calculate, but this will add tens of millions also.
So who is happy with this strategy? I can’t understand it, it only makes sense if you assume that no future generation will ever want to bury SH1, pouring that traffic onto congested city streets is okay, and the urban environment can be damned. So at this point I’ll describe two alternate approaches I think we should all be seriously considering before we break any ground at the Basin Reserve.
The first is the incremental approach. Of course this approach would’ve been much easier going in the eastwards direction, but now we have to work around the ICB. This approach requires us to build a tunnel instead of a flyover at the Basin Reserve. This would be a variation of Option G, constructing a wider tunnel to allow future bidirectional traffic, and a stub at the western end to allow for extending the tunnel without interruption. It could also include an entrance from Kent Tce. This would probably cost something in the vicinity of $400 million. This would be followed with the Mt Victoria Tunnel duplication at $432-492 million, then the extension of the Te Aro tunnel at another $430 million.
This approach carries a higher up front cost, but we do get the benefits of improved westbound traffic flow and a far superior urban design outcome for the Basin Reserve and Memorial Park. We get improved space at the Basin Reserve for dedicated PT lanes. If/when the tunnel is extended we will not have to face a duplicated flyover at the Basin Reserve, and disruption will be considerably reduced with no need to demolish the Memorial Park. The drawback is that we will need to maintain ownership and possibly acquire new property along the route of the tunnel extension.
The second approach is for us to give up on trying to shoe horn a series of ad-hoc state highway improvements into this corridor, and go for a complete solution by burying the state highway in a deep bore tunnel. This approach would provide greater long term benefits, but it’s a much bolder strategic move requiring big cajones from the politicians and planners involved. It would start with us completing improvements to the Basin Reserve to improve traffic flows without the expensive and undesirable flyover. These at-grade improvements are aimed at simplifying and streamlining traffic flows to see us through the next decade while traffic volumes are predicted to stay static or possibly decrease. It would see us forgo the duplication of the Mt Victoria Tunnel in future, and instead construct a deep bore tunnel between the Terrace Tunnels and Kilbernie to carry all SH1 traffic. Vivian St and the ICB would continue to carry traffic exiting/entering the city from the CBD, but these surface streets and the Basin Reserve will have plenty of capacity now that the SH1 through traffic removed from them.
This approach would be the least disruptive, utilising TBMs to carry out most of the work under the city while day to day business carries on as usual. Ruahine St and Wellington Rd would no longer need to be widened, and Karo Dr could be removed and straightened to link Aro St with Arthur St, reestablishing the Te Aro street grid. By adopting this long term plan the city can begin to heal the scar along the existing ICB route with confidence that it’s permanent. The deep bore approach would see $40-50 million spent on at-grade improvements (a variation on Option D), followed by a 3.25 km deep bore tunnel at around $1,300 million  for a total of around $1,350 million. Now this approach also has the added benefit that we can easily collect tolls from users because the deep bore tunnel to provide additional funding to complete the tunnel earlier.
This is where I think it’s critical we answer the question: do we want the option of putting SH1 into a tunnel in the future? I suspect many would prefer to rethink the current strategy and see one of the other approaches above adopted. Here’s how I think each of our three camps would rank these three strategies.
The motorists would prefer the incremental approach the most because it gives immediate benefits and is unlikely to be tolled. They’d prefer the deep bore approach second because it provides a faster journey. They’d prefer the current strategy the least because it is unlikely to ever result in a fully grade separated SH1.
The public transport advocates would prefer the deep bore approach the most. It doesn’t pour money into new roads and it makes simple upgrades that are sufficient for the next decade during which time they argue traffic is likely to stay static if not decrease due to the impacts of peak oil. Over this time improvements to public transport will be made and they may even find by the time comes around to build the tunnel it is no longer necessary or can be delayed. They’d prefer the incremental approach second because it allows us to have a better configuration for light rail and busses at the Basin Reserve.
The urbanists and residents would prefer the deep bore because it is the least disruptive during construction, and requires the least number of properties, does not require any flyovers, and does not widen streets. It allows the reestablishment of the street grid, and for the ICB scar to heal. They’d prefer the incremental approach second because it doesn’t require a flyover, and gives a better result for the Basin Reserve and Memorial Park, with a less disruptive upgrade path to a full tunnel in the future.
So if I’m right that puts the deep bore option ahead of the incremental option, with the current dead end strategy in last place. Why are we following this dead end strategy? Feasible Options Report, January 2011.
 Mt Victoria to Cobham Drive Scoping Study – Technical Report Cost Estimate, May 2011.
 War Memorial Tunnel Scoping Report, December 2010.
 Pro rata rate of $600 thousand per meter was derived from the $290 million cost for Option G and increasing cost by a factor of %50 to account for additional width. Not particularly scientific, but should provide a reasonable first order approximation.
 The Waterview Connection in Auckland can give us some guidance to the costs of deep bored tunnels. NZTA wouldn’t reveal the estimated costs for the tunnelled section until after the tendering is complete, but we know that the project includes twin-bore 3-lane tunnels at a length of 2.5 km, with other surface sections, and widening of the Northwestern for an estimated cost of $2 billion. If we assume $1.5 billion of that is just the tunnels, and an efficiency factor of around 1.5 for boring two tunnels versus just one we get an approximate cost of $400 million per kilometre. This appears to compare well to overseas projects, such as Madrid’d M-30 project (very cool to drive through, sorry no pictures).