Readers of my recent post may recall that I’m no fan of the proposed second harbour crossing. That has a lot to do with the fact it would actually be our third harbour crossing, and our third motorway crossing at that. With traffic levels static on the Upper Harbour Bridge and actually declining on the Auckland Harbour Bridge it seems a little silly to be planning yet another motorway across the harbour, especially once we consider how effective the busway has been.
It’s not actually a case of fewer people crossing the harbour each day, that figure keeps climbing, it’s just that all the growth has occurred on public transport. More and more people cross the harbour each day… on a bus. This begs the question, why aren’t we planning a public transport crossing? A projected cost of more than five billion dollars for a harbour tunnel and it’s all just for cars and trucks. Something needs a rethink methinks.
The real problem with proposals like this is that they just won’t go away. No matter how poor the business case, how low the BCR (around 0.2 to 0.4 if you’re asking), no matter how damned expensive… I just can’t shake the resignation that sooner or later this motorway tunnel is going to get built anyway. All it takes is one minister to start using words like ‘policy alignment’ and ‘strategic fit’, and all the extensively researched economic evaluations aren’t worth toilet paper.
With that though in mind I went back to the drawing board and started to think about how we could really make a harbour tunnel work. If it abso-friggin-lutely has to be built come hell or high water, what can we do to make it a real bonus for Auckland? How can it also improve public transport, walking, cycling and urban design?
After all, it’s not like this megaproject couldn’t have some additional benefits. For a start the plan is for the tunnel to carry State Highway 1 though to Spaghetti Junction and leave just citybound traffic on the existing bridge. If they do this right the new tunnel would function as a bypass of the CBD, by taking all that heavy traffic and sending it underground and out of the way. With only city bound traffic on the bridge we could reallocate a pair of its lanes to buses, and without heavy freight traffic we would have enough strength in the clip-ons to add the proposed walking and cycling path.
More excitingly, without any need for a link between the bridge and the other motorways we could tear down the Victoria Park viaduct and free up that corner of the city. The remaining Victoria Park tunnel could be reused as a two-way link for traffic through to Cook St, perhaps even taking the bulk of traffic off Fanshawe St. In any case we could almost halve the number of lanes through St Mary’s Bay, if those lanes need only enough capacity to service the city streets and not the motorway.
There might even be a case for demoting the St Mary’s Bay motorway to an avenue style expressway, a sort-of western version of Tamaki Drive extending from a revitalised Fanshawe St boulevard. Auckland’s city waterfront could then stretch right across to it’s natural anchor at the foot of the bridge. I can see it now: rows of leafy trees, a stretch of waterside grass, cyclists whizzing along to the North Shore, kids eating ice creams as mums and dad watch the comings and goings of the marina and the harbour.
This all sounds very good, positively bucolic even… but truth be told we’re not really getting much value out of this yet. Five billion bucks to get some bus and cycle lanes on the bridge and tidy up the waterfront? To be frank that is the sort of thing we can do anyway at a much lesser cost, we don’t need a motorway tunnel for that. If we really want to get value out of a harbour tunnel it has to carry public transport, and I mean proper high capacity and fast rapid rail transit. Nothing else is going to move enough people to swing the numbers. Adding a rail line to the motorway tunnel could triple it’s carrying capacity at very little extra cost, if only some space could be found inside the same pair of tubes.
If we look at NZTA’s most recent proposals we are actually talking about some pretty big holes through the ground. One of the issues with boring a tunnel like this is that motorway lanes are basically rectangular in cross section, while tunnel bores are circular. It’s very much a case of fitting a square peg into a round hole. In this case the round hole will apparently need to be about 15.5m in diameter to fit in a square peg 12m wide and 4.5m tall.
That’s quite a lot of tunnel indeed, and in fact some of it ends up wasted. I’ve clarified the labels there because they are too hard to see, but the bottom right corner of the cross section is simply ‘cement stabilised backfill’. In other words that is just a mix of concrete and dirt poured back into the tunnel to hold the road deck up. Could we not put this space to better use?
Closer inspection of the cross section reveals the sorts of things you might expect in a tunnel: lights, fans, smoke extraction ducts. But underneath the road deck there is also a sump area to extract water, and a cable tunnel to carry pipes and wires across to the North Shore. That cable tunnel is actually pretty big, about 4m tall and 3.5m wide, could we fit a train through there? Probably not one of our new electric trains, they’re a bit too big and their overhead power lines need more height. But I do think a more compact light metro vehicle would fit in comfortably, particularly as they have a low floor height and get their power from between the rails instead of an overhead wire.
This picture shows a Bombardier ART driverless metro train to scale in that same cable tunnel, nestled in under the road deck. Instead of backfilling the empty space under the road, I’ve used it to relocate the cable tunnel to one side. This could also double as an emergency exit, or an access path to whatever emergency system they would have to install in the motorway tunnel anyway.
Basically, it seems with a little rejigging of the layout of our big harbour motorway tubes we could also fit through a light metro line to the North Shore. Given that it’s the same pair of bored tunnels, this rail crossing could be tacked on for minimal extra cost.
Now I must say I am no civil engineer and I couldn’t confirm if this is actually feasible, but a quick looks suggests that we very well could get both three motorway lanes and a driverless light metro track into what NTZA were proposing to build for the motorway alone. The benefits of this would be immense.
Three motorway lanes can carry about 6,000 vehicles an hour at best, which at our occupancy rates translates into about 7,500 people. The light metro systems in Vancouver and Kuala Lumpur currently carry about triple that on each track at peak times, and can theoretically move well over 30,000 people an hour each way.
Stacking metro tracks in under the road decks could easily quadruple the person carrying capacity of a harbour tunnel, and one can only imagine what that would do to the cost benefit ratio. If we must build a hugely expensive motoway tunnel under the harbour, then a shared motorway and metro tunnel could be just the thing to make the numbers stack up too.