Reader mailbag: really long tunnels edition

I'd been wondering about the proposal to dig a really long tunnel to route through traffic away from Wellington's central city. 

It seems the kind of thing that you might decide to do, after running congestion charging for a while and seeing that the project is warranted, rather than deciding on ahead of having that information from revealed preferences and prices. The thing won't be cheap. 

So I was happy to see this in my inbox this afternoon to help me think through it. 

The Wellington Long Tunnel could be a transformative project to take enough traffic out of the city, especially Te Aro, but also the Quays along the waterfront and Oriental Bay, to improve amenity, relieve congestion at bottlenecks at the Terrace and Mt Victoria Tunnels and make it easier to walk and bike, as well as move buses, delivery vehicles (and cars) within central Wellington. Plenty of other cities of broadly have taken traffic out of their downtowns through purpose-built bypasses, such as Bergen, Antwerp, Basel and Tampere. Bergen is paying for some of the cost of its bypass with a toll.

Saving 15 minutes between the airport and the Hutt, Porirua and the rest of the region seems worthwhile, but both the travel time (and fuel) savings, and uplift of amenity would come at considerable cost. In 2021 Let’s Get Wellington Moving estimated the project might cost $3.1b, but we know how reliable such forecasts have been lately.

Yet it poses the obvious question. If Wellington got time-of-use pricing (congestion pricing) introduced during weekday peaks, focused on the CBD (leaving SH1 out of it as a bypass to a cordon), would the change in behaviour it enabled be enough to relieve congestion on SH1, and so determine then if the Long Tunnel idea was still worthwhile?

The answer is probably yes, although high-level modelling of a cordon pricing option by LGWM suggested that travel times southbound on SH1 would worsen, it would appear because the Terrace Tunnel has insufficient capacity in that direction (one-lane) to accommodate the traffic redirected around the CBD off of the Quays. That could be addressed by putting a higher price on that traffic which could justify building more capacity at that bottleneck.

However, it’s one thing to think of how the roads might be run as a rational business, but reality has some complications:

1. The Long Tunnel is about more than traffic. Arguably it can unlock property value uplift by removing a lot of traffic from existing streets, including taking a lane each way off of the waterfront route to enable a second public transport corridor along it, and more development along the waterfront, as well as removing much of the blight of traffic from Te Aro. The value of all of this is unknown, but as the Long Tunnel is as much about amenity as transport, it is important although caution needs to be taken around exaggerating these benefits (as much as applies to those pushing light rail’s benefits).
2. Congestion pricing for Wellington should probably exclude SH1 for public acceptability, at least at first. A downtown cordon is relatively easy to implement, as trains and buses pretty much all converge on it, and most drivers have reasonable alternatives. Having a good bypass helps to encourage traffic to flow more efficiently around the priced area (this has been seen in Stockholm and Oslo), although it would be wrong to wait until the Long Tunnel is built before introducing congestion pricing.
3. Politics around use of the money. Greens want congestion pricing to raise money to pay for public transport boondoggles, it seems likely National wants it to pay for road boondoggles. Arguably, a road boondoggle that at least benefits those paying the congestion charge is a better waste of money than one that doesn't. It would be better to use pricing revenue to offset rates funding of roads, or enable lower off-peak pricing of roads (if RUC was set by location), or just used for the best projects to upgrade roads in the region, but no jurisdictions do this.
4. The politics around building a Wellington bypass. For over thirty years the issue of fixing the route between the motorway and the roads approaching the airport has been highly politicised.  The current road layout generates congestion all-day during weekdays and much during weekends, and is clearly inefficient as it encourages diversions along routes not well suited to through traffic. The Basin Reserve is the biggest part of that problem, and indeed past BCR assessment of proposals to upgrade it indicate that fixing the Basin Reserve is worthwhile. If the Basin Bridge had been approved by the Key Government, then we probably wouldn’t be talking about the Long Tunnel, but the politics around putting a bridge between Mt Victoria Tunnel (including a new one) and the Arras Tunnel (and maybe a new one to take eastbound traffic off of Vivian St) are complex.

The Greens and Mt Victoria Residents who want nothing built. In Wellington, stopping the “motorway extension” was a cause celebre in the 1990s for the Greens (in their formative years) that succeeded largely due to fiscal constraints, and we are where we are as a result. However, there are also allies in friends of the Basin Reserve who love that cricket ground. The Minister for Infrastructure is one of those people.  The below ground conditions at the Basin are not conducive to tunnelling underneath because of the geology including an underground stream, so it’s a bridge there or a deep tunnel somewhere else. The Minister of Infrastructure is likely to not look friendly upon a bridge (although I wonder if putting a artificial hill to the north of the Basin to conceal a bridge might fix that). 

Unfortunately, the politics around "build no new road projects because cars are bad" from most of the Greens, encourages the Nats to go the opposite "quick build a big project so they can't stop it, and when it opens everyone loves it”.  This transport culture war (which Labour tended to not be a part of, as seen by the road building under the Clark Government) generates a reflex response to build more and bigger.

If there were a more rational, bi-partisan approach, then Wellington could get congestion pricing, a bridge at the Basin Reserve, and perhaps more incremental improvements to SH1 built as merits stack up.  Of course, that wouldn’t deliver the “big bang” amenity transformation of a single big tunnel, but it would likely deliver most of the travel time benefits, many of the amenity benefits, with the only question being whether the costs of disruption and construction in building a cut-and-cover tunnel between Vivian Street and the Arras Tunnel start to rival the Long Tunnel.

This is where the focus of NZTA’s investigation should be in the coming months:

1. Model Wellington traffic with congestion pricing to the downtown (and then again on SH1)

2. Estimate the costs and benefits of the Long Tunnel vs. incremental upgrades to the existing alignment, and whether the transport user benefits and amenity/property uplift benefits are worth it.

I still like the structure that was set out in the 1998 Better Transport, Better Roads proposal.