In the fallout from the release of the City Centre Future Access Study last Thursday and the government’s rather bizarre response to it, for some reason there seems to have been renewed discussion about the Additional Waitemata Harbour Crossing (AWHC) project. It’s a bit odd to think that if Central Government has concerns about contributing to a $2.4 billion project they’d end up looking more kindly on a $5 billion project instead, but I guess as it’s a road rather than a railway line you really never know.
We’ve discussed the AWHC project on this blog many times before, most particularly recently pointing out some incredibly dodgy traffic statistics used by NZTA to help justify the project. In this post I’m not really going to focus on the cost of the project, or the heroic traffic growth assumptions or even why a rail crossing is a much more sensible option. What I’m going to simply look at is the likely traffic effects of the additional crossing – where it does and does not add capacity to the system and what the impacts of that are likely to be. There’s a wealth of information on the project website, which I will draw on to inform this. For a start, let’s just get a rough idea about what the AWHC project is – something that’s reasonably well illustrated in the diagram below:It’s a little complicated with all the different colours, but let’s just think about what happens for southbound traffic:
- Traffic heading to Shelly Beach Road, Fanshawe Street and Cook Street uses the existing Harbour Bridge
- Traffic heading to SH16 west and SH16 port exits uses the new tunnel
- Traffic continuing south on SH1 uses the new tunnel
The same is obviously also true in reverse. Oh an by the way I wouldn’t get too excited about the rail tunnel shown above – the fact that a shuttle line from Gaunt Street to Akoranga is shown, with no connections to the existing or proposed rail network at the city end, just illustrates that it’s only in there as a token gesture.
At the moment in the morning peak there are five lanes southbound coming over the harbour bridge. The Shelly Beach Road offramp peels off but the five lanes remain through St Mary’s Bay. Then one lane drops off at Fanshawe Street and four lanes continue southbound over the Victoria Park viaduct: two of those feeding into Cook Street and the SH16 exits and the other two linking with the Southern Motorway for trips heading further south. Ignoring the city exits (Shelly Beach, Fanshawe and Cook Street) for a minute, it’s clear that there are four lanes that link the Harbour Bridge through to SH16 (for east and west travel) and SH1 for travel further south. Here’s a diagram showing the future layout of the motorway network with the AWHC built:
It’s a bit confusing at first, but once you ignore the local roads it starts to make a little more sense. We can see that southbound in the morning peak there would be three lanes in the new tunnel and four lanes (one of which is a bus lane by the look of it) coming over the harbour bridge. The new tunnel effectively removes ‘through traffic’ from the Harbour Bridge, but doesn’t actually add any capacity over what already exists for that through traffic.
- There’s still only two lanes which continue right through for southbound traffic.
- There are only three lanes (compared to the current four) for traffic heading to either SH1 southbound or the SH16 exits.
What the new road does do, of course, is free up huge amounts of new roadspace for vehicles travelling from the North Shore to the CBD. There are now four southbound lanes over the harbour bridge worth of capacity – all of which can only link to Shelly Beach Road, Fanshawe Street or Cook Street. That’s potentially an absolute flood of additional vehicles that could be funneled into central Auckland because they no longer need to ‘compete’ with the through traffic for roadspace over the Harbour Bridge.
This impact is well documented in the project’s Local Roads report:
The main challenge for this assessment relates to the provision of additional capacity across the harbour and the potential flow on effects this may have on the local road network around central Auckland and feeder roads on the North Shore, particularly in the weekday morning peak. In particular it is noted that the new harbour crossing will allow more traffic to enter the CBD. This conflicts with various CBD strategies that encourage the provision of public transport for trips to/from the CBD and not to provide additional capacity for cars.
It fundamentally conflicts with the concept of a liveable city centre.
It is anticipated that space on the existing Harbour Bridge will be allocated to public transport, walking and cycling, if an Additional Waitemata Harbour Crossing is provided. The precise lane configuration on the existing Harbour Bridge will only be determined over time and this will significantly affect the predicted traffic effects of the additional crossing. The scenario agreed for this study (for both bridge and tunnel options) includes the following lane allocation on the existing bridge:
- One lane for walking and cycling;
- A bus lane in each direction, but with general traffic heading to the Shelly Beach off ramp sharing the southbound bus lane; and
- Five general traffic lanes in total, assumed to operate with three southbound and two northbound lanes in the weekday morning peak, with the reverse in the evening peak.
This scenario would provide three southbound lanes for general in the weekday morning peak plus additional capacity, equivalent to around half a lane, for general traffic heading to the Shelly Beach off ramp. This scenario also provides the opportunity for a significant increase in the rate of flow from Esmonde Road (and Akoranga Drive) onto the Northern Motorway, thereby increasing the rate of flow able to cross the Harbour and reaching the Auckland CBD.
It’s hard to know whether to laugh or cry about the fact that even after spending $5 billion NZTA still can’t bring itself to providing a proper dedicated southbound bus lane. The important thing to note from the above paragraphs though is at the very end: the real impact of the project is a massive increase in flows from the North Shore into the CBD. As no additional capacity is provided south of the CBD the are few gains there aside from being able to hit the gridlock through spaghetti junction a bit quicker because vehicles travelling through the tunnel no longer need to compete for roadspace with those heading for the CBD.
It seems as though the report writers began to realise this fundamental flaw with the project and therefore ended up recommending retaining some measures to limit the flow of vehicles onto the motorway from the North Shore:
A range of options could be used to limit the rate of flow able to cross the Harbour, including changes in the lane allocation. However, for the purposes of this assessment it has been agreed that the effects of the additional crossing will be assumed to be restricted by some means and that this should be reflected by modelling ramp signals on the important Esmonde Road southbound on ramp. Capacity constraints are already predicted to exist on the approaches to or on the other on ramps during the morning peak, and providing ramp signals at Esmonde Road will therefore further constrain the rate of flow able to pass across the harbour and into the Auckland CBD.
So we’ll spend $5 billion on adding a huge amount of capacity across the Waitemata Harbour but we’ll still need to use things like ramp signals to limit the flow of vehicles onto the motorway – doesn’t that kind of defeat the purpose of the whole project?
The impact of the project on some city streets is pretty massive in terms of additional vehicles – especially Fanshawe Street and Cook Street (Curran Street and Shelly Beach Road, two residential streets, get slammed as well):To cut what is becoming a pretty long story short, it really does seem as though the AWHC project involves spending $5 billion to make it easier to drive your car into the city centre – something we actually don’t want you to do. In other words, it is building the most expensive transport project ever to create more congested inner city streets and a less liveable city centre. It’s a huge amount of money on something that will make Auckland a far far worse city.
For that reason, it is quite simply the stupidest transport project ever.