Many of the debates over the City Rail Link’s cost-effectiveness have revolved around the question of rail capacity. At what point does the railway network, without the CRL, become overloaded? How many people will be discouraged from taking the train because of this overcrowding? If they go back to driving, what congestion would they create? If they go back to catching the bus, what congestion does that create? All these sorts of questions are at the core of how, in particular, the Ministry of Transport undertook its review of the project’s cost-benefit analysis.

That’s how you end up with complicated tables like this:

In case you’re wondering why there’s nothing for the eastern line, it’s because the Ministry of Transport’s analysis showed that even without the City Rail Link, there was enough capacity in the rail network for Eastern Line trains right through until 2041. Yes, seriously.

A lot of the detailed analysis of the City Rail Link’s cost-benefit ratio confuses me, because – as I explained in this recent post – all the analyses make one big assumption: that car and bus capacity is unconstrained. What that means is that the modelling used to estimate the number of people catching the bus, train or driving into the city centre in future years does not have, as a part of its workings, anything which says “at a certain point the roads will be full of buses and cars and you can’t fit anymore in.”

What this means is that all the business case assessments of the project so far assume that the number of bus passengers in particular, will increase dramatically in the future – both in the “2041 with the CRL” and “2041 without the CRL” scenarios:
You get some idea what this might mean on the ground through the maps in this report, prepared by NZTA to inform the Waitemata Harbour Crossing Project. Firstly, looking at the number of buses we have not along key routes in the AM peak: The colour of the arrows are explained further in the table below: What this suggests is that above 80 buses an hour you start to get issues, and over 100 buses an our things really start to get problematic – requiring multiple lane busway operations that simply aren’t feasible in Auckland’s city centre.

Keeping this is mind, if we look at the “2041 no City Rail Link” scenario, we can see that the number of buses that would flood the city centre is completely infeasible: If running over 100 buses an hour along arterial roads is problematic, then running two or three times that number along Symonds Street, Albert Street (both ways) and Fanshawe Street is, quite frankly, impossible. As someone I was talking to earlier this week said, as this point you’d need people sitting on the roof of the bus for such a scenario to make sense. So the map above makes a good argument for the necessity of the City Rail Link (and possibly also a North Shore Line).

However, it’s the next map which is perhaps even more interesting – the number of buses in the “2041 with City Rail Link” scenario: While buses coming in from Grafton Bridge have reduced down to a more feasible level, we still have a completely impractical number of services coming in from Upper Symonds Street, we will have a huge number of services both ways along Albert Street and, obviously, we’ve done nothing about the North Shore issue.

The impossibility of running so many buses along Albert and Symonds Street, even in the “with CRL” scenario, means that these passengers would have to travel by some other means. Travelling by car is pretty infeasible, as we will have dedicated so much roadspace in the CBD to bus lanes to handle the North Shore buses, as well as whatever we find to be the actual maximum number of buses from the south and west the city’s streets can handle. Also, if we’ve started giving effect to the City Centre Master Plan, much more of our city’s roadspace will be dedicated to pedestrians. The train is the only feasible alternative.

This potentially has a huge effect on assessing the cost-effectiveness of the City Rail Link. Let’s analyse what the capacity of the city centre for buses and cars might actually be:

  • In 2010 there were around 34,000 car (including drivers and passengers) trips into the CBD at peak times. If we think about the City Centre Master Plan reducing roadspace throughout many parts of the city centre (like Quay Street, Queen Street, Hobson/Nelson streets and Victoria Street), as well as having to give up roadspace to bus lanes to accommodate the significant increase in bus numbers, I think a future car capacity of the CBD is unlikely to be much more than 30,000.
  • In 2010 there were 23,000 bus passenger trips into the CBD at peak times. Most of these end up along Fanshawe, Albert and Symonds Street, which are all getting reasonably close to that 100 buses per hour capacity limit where things start to not work particularly well. Improved bus routes within the CBD (such as taking all North Shore buses off Albert Street and sending them via Wellesley Street instead) should allow for a fairly significant increase to this number, but certainly not more than half as many buses again. So let’s say a capacity of 35,000 trips at peak times.

If we set these car and bus capacity constraints, we see a huge impact on the number of rail trips. The three assessments done disagree on the total number of trips into the CBD at peak times in 2041 (excluding walking and cycling), but we can take an average of the three to come up with just under 105,000. Assuming ferry patronage increases from 3,000 to say 5,000 – you start to see that the rail system will have to take a pretty massive number of trips.

In the “2041 with CRL” scenarios, none of the assessments done suggest that rail will have this many trips – simply because they haven’t recognised the capacity constraints on the city centre’s road network. Therefore, all the assessments have under-estimated the impact of the project, they have significantly under-estimated rail patronage and therefore it is likely that they have all under-calculated the project’s real cost-benefit ratio.

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  1. This is the very reason why a large numbers of international cities are trying very hard to increase cycling numbers through bike share and best practice cycling infrastructure. There is a limit to the vehicle capacity of cities and they simply cannot build infrastructure quick enough to cope with demand. Cycling infrastructure has the best ROI of any transport infrastructure and it has massive capacity if done correctly – providing both subjective as well as statistical safety.

  2. This also highlights one of the problems with the suggestion recently that a bus tunnel would be better. Bus tunnels overseas can accommodate around 150 buses per hour per direction or about 300 per hour all up, the suggestion was that a two lane busway would be able to handle 500 buses per hour was simply insane.

    1. Well, it’s feasible. At 80km/h, a two-second following distance is 44m. A 13 metre-long bus therefore requires 57 metres of road. Two lanes would have a capacity of 2880 vehicles per hour, at absolute maximum capacity, but with no allowance for any hindrance to flow; it’s pure free-flowing traffic.
      In practicality, though, you’re right that it’s completely insane. There’s no safety margin for slow vehicles, or breakdowns. The slip roads necessary to allow all buses to reach 80km/h before merging would be so long as to effectively make the network two roads, not one. Even at 500 vehicles/hour it’s pushing safety to the limit.

      1. The issue isn’t so much the road itself but the stations, just take a look at some of the busy bus corridors in Auckland at the moment and you will see that it is a kind of chaos and slows things down

    2. It’s surprising how many myths of capacity are promulgated by BRT proponents. Actual research on Brisbane’s busways has shown that for an average loading of 10 passengers per bus, the capacity is just over 100 buses per hour (see Fig 8.2 in the reference with the link below). The bus throughput capacity drops further as more passengers load at a stop. Busway stops similar to those on most of Brisbane’s busways (and proposed for an Auckland busway tunnel) simply cannot cope with high CBD boarding numbers. Brisbane used a much more expensive design for its CBD bus station, and spent $330m for a bus station (King George Square) with designated multiple loading bays that takes only a third of the bus routes on the southern busway.

      At 40 passengers per bus and 100 buses per hour, the capacity of a busway tunnel is less than one third that of a train tunnel, the main difference being the higher loading rate of a train. Busways are a great way of making existing bus routes faster, but are not a direct substitute for a train tunnel.

  3. What sized busses are assumed in the arrow diagrams above? I ask because the B’head buses that I catch have a capacity of about 60, where as you can get capacities of double this. So there is quite a bit of potential for increasing bus capacity without increasing bus numbers. Also with integrated ticketing, ferries would appear to have high growth potential, particularly with development out west

  4. Great work at looking at how the 3 main modes interplay in reality. Interesting to see that they don’t seem to have factored this in.

    With the North Shore buses I see that you have mentioned Wellesley St. I heard that there was a possible bus interchange planned there on a smaller scale than Britomart. The only weakness I can see to this is that buses are a bit more focussed on Midtown for Shore-ites – not great for the reasonable proportion who presumably work downtown. Other option is to mix destinations using Cook St offramp as well as Fanshawe/Albert and Fanshawe/Wellesley. Would be a bit ugly in terms of trying to aim for improved route simplication, but would spread the number of buses a little better.

    Not sure if Hobson or Nelson Streets have been looked into as other option for a bus lane. Tricky to work in with the car traffic presumably. Does anyone have any thoughts on this?

  5. Bus congestion in the CBD is already really bad, i’d hate to think what it might be like by 2041! They are a hazard for cyclists, they are terribly noisy, have massive turning circles at traffic lights and create lots of fumes. I believe if there were less buses in the CBD we would be one step closer to being the most liveable city. I’ve come up with a monobeam monorail concept from Newmarket along broadway, khyber pass, symonds, wellesley and albert sts to Britomart based on the SkyCabs Company design which i think could work very well. It involves most of the southern buses to downtown terminating at the end of Great South Road and Manukau Road where the monorail would start and then a second terminus on Upper Symonds Street cnr Khyber Pass and Newton Road for most central services. Usu people don’t want to transfer so it would have to be made as easy as possible. The skycabs concept can have a monorail car arriving every 6sec with a seated capacity of 8 people so it is easy and fast, much faster than by bus, and people will actually want to use it. I can put a post about it if you like.

  6. There is a whole PhD thesis devoted to modelling busway capacity, based on observations at one of Brisbane’s busway stations (link below). If 10 or more passengers board per bus, the capacity of a 3-bay bus station is 100 buses per hour if there are no traffic lights, and 50 buses per hour if there are traffic lights with 50% green time. It would be great to ask Stephen Joyce if such studies were taken into consideration in the benefit-cost calculations. These and the omissions you have pointed out above would be great questions for a Green member to ask on notice in Parliament !

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