In Matt’s recent post about MoT’s work on the future of transport, there was an interesting little side-discussion about transport models, and in particular the travel demand forecasts which emerge therefrom.

We’ve previously written about the accuracy of transport models when used for project evaluation purposes. Perhaps the most notable (notorious?) was this post on the Waitemata Harbour Crossing, where we discussed how NZTA’s business case used traffic volumes that were approximately 10% higher than actual volumes. Naturally this led to the benefits of the project being overstated.

More recently, this post on the SH20 Manukau Harbour Crossing found it was carrying approximately 45% less traffic than projected 10 years after it was complete.


Transport models are important not just for the purposes of project appraisal. The outputs of transport models are also used to forecast aggregate travel demands and determine policy at a much higher level. For example, the MoT and the NZTA use (different) transport models to forecast aggregate vehicle kilometres travelled, which in turn determine the funding that is available in the NLTF to fund the projects identified in the NLTP. Hence, our ability to plan ahead is influenced by transport models.

In this context, graphs such as the one below are something of a cause for concern.

But let’s not be to critical of the MoT and NZTA; they are not alone insofar as their transport models have consistently over-estimated demand. Graphs surprisingly similar to that above exist in the US and the UK; one such example is shown below.

In some earlier posts here and here, we’ve presented some possible reasons for what might be causing the transport models that are used for forecasting travel demands (both at the level of individual projects and in aggregate) to get it wrong. The systematic positive bias in forecasting errors has been the subject of formal academic research led by the Danish economist Bent Flyvberg. I presented a paper at last year’s IPENZ Transportation Conference in which I discussed some of these issues in more detail, while Peter wrote an excellent post on the topic here. His analysis of NZTA data suggests that New Zealand may not be immune to the same systematic biases found overseas.

This post, however, is not about the systematic positive bias into transport models. Instead, this post is about whether the mechanics of the models are capturing what they need to capture in order to formulate accurate predictions. I think this is a useful starting point for thinking about “transport futures”, as the MoT seem keen to do.

I also think it’s fair to say that the superficial explanation for the slowdown in the growth of aggregate vehicle travel is that per capita vehicle travel has been on the decline. That is, people (both in New Zealand and overseas) aren’t driving as they used to. But this doesn’t get us very insofar as predicting the future, i.e. observing that per capita demands are declining simply begs the question of why?

And this is exactly where things start to get interesting. In my time thinking about these issues the views that are expressed tend to be readily grouped into one of three broad categories, which I now present for you to consider.

First we have what I call the “establishment view“, which is led by the likes of the MoT, the Government more generally, and a number of consultants. This view argues that the decline in per capita vehicle travel primarily reflects higher fuel prices and reduced economic activity over the last 5-10 years. There’s obviously some logic to this view; it seems reasonable to suggest that both the cost of fuel and the state of the economy will impact on travel demands, at least in the short term (say 1-5 years). Where the establishment view struggles, however, is to explain why the slowdown in vehicle travel started so early (way back in 2005), and why volumes haven’t bounced back more strongly of late. The latter is particularly interesting given NZ’s robust levels of economic growth, strong population growth, and sustained low fuel prices.

While VKT is currently growing again, it doesn’t seem to be growing by as much as one might expect based on these factors.

Which leads me to the second view, which I call the “wider socio-economic view“. This is probably the position which best describes my own views, at least in terms of understanding travel demands in the medium term (say 5-10 years). This view looks beyond the hard economic factors considered by the establishment view and instead consider some wider factors that seem likely to impact on the demand for vehicle travel. People who subscribe to this view will often talk about the following issues:

  • Demographic factors, such as an ageing population and changes in the number of people with drivers licences;
  • Transport and land use factors, such as availability of public transport and the ongoing intensification of our cities; and
  • Vehicle substitutes, such as air travel and telecommunications.

The wider socio-economic view complements the “establishment view” in some senses, because it appeals to similar micro-economic mechanisms, but it does so in a way that allows for a wider range of factors to impact on the demand for vehicle travel. In doing so, however, the socio-economic view can lead to predictions that are quite different to those of the establishment view. Instead, the socio-economic view allows quite a lot of room for future growth in aggregate vehicle travel to differ from what we’ve seen in the past – which is something the establishment view struggles to incorporate.

Finally, we have what I call the “changing preferences” view. This perspective interprets the declining per capita demand for vehicle travel as a function of wider shifts in people’s underlying preferences. This view emphasises, for example, that young people are now placing a higher value on other forms of consumption, such as the connectivity offered by smart phones, than the personal mobility associated with owning and operating a vehicle – at least compared to their parents. The changing preferences view would seem to suggest the trends we’ve seen in the last 5-10 years are just the tip of the ice-berg, and that profound changes are just around the corner. Often people highlight that it’s not just technology which is driving these changes, but also awareness of the health and environmental effects of driving. Evidence for this view were recently summarised in this NZTA research report, which we previously discussed in this blog post.

The following figure is taken from this report.

Which view to believe? Well, personally I think all three have elements of truth to them. I think the establishment view is correct insofar as certain price and economic factors are likely to dominate changes in travel demands in the short term.

In the medium to long run, however, the other two views presented above seem to have more currency. I mean, if fewer people have drivers licenses then it seems plausible to suggest that there will be a reduction in per capital vehicle travel, ceteris paribus. Similarly, we can expect reductions in the cost of air travel to eat into the demand for long distance vehicle trips. In terms of preferences, these are critical to the accuracy of any model that seeks to forecast future demands based on past behaviours. If preferences changes, then our predictions are resting on a wobbly plank over shark-infested analytical waters.

So what’s the takeaway message? Well, I think it’s fair to say that we simply don’t know what to expect with regards to the future demand for vehicle travel.

In this context, I personally wouldn’t be investing in large transport projects, especially in rural areas, e.g. Puhoi-Wellsford, Waikato Expressway etc. As for the CRL, I think it’s likely to be a good project because of 1) patronage growth on the rail network, 2) Auckland’s growth as a whole, 3) the explosive growth in the city centre (both in terms of population and retail), and 4) wider trends in transport and land use policy, e.g. time-of-use road pricing and removing minimum parking requirements.

But I’m open to being convinced either way, and am interested to hear what others think on all this.

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  1. NZTA traffic counts (for state highways) now show 10% growth in traffic overall and 7.5% increase in heavy traffic. Perhaps city traffic is still flat, but it seems thats not the case for traffic on state highways since 2012.

    1. Heavy traffic numbers fascinate me. Buses are counted as heavy traffic, I believe, so the strong growth in the Northern Busway, for example, adds to Heavy count on the bridge [SH].

      The RoNS construction work, especially where they involve huge cuttings, tunnelling, causeways etc; generate massive round the clock truck movements. The work on SH16 and 20 now, the Waikato expressway, Tauranga etc. To what extent does current spending of the NLTF feedback into justifications for more of the same spending?

  2. There are two additional reasons that the ‘establishment view’, if a sufficient explanation, would lead to the expectation of a powerful the bounce back in driving now with lower fuel prices.

    1. Vehicles themselves are cheaper, they last longer more reliably, and are more economical to run.

    2. This century many multiple billions of dollars have spent on easing and facilitating driving through shiny new road infrastructure.

    Nowhere has the response to this spending been met with anything like the open-armed glee that the public has treated the upgrade to Auckland’s still stunted little rail network. This contrast suggests the other forces Stu mentioned above are likely at work; urbanisation, preference.

    1. Despite the constant council bashing, public support is insanely in favour of improving PT

      It’s the same in Melbourne, and even some US cities. Local governments also tend to favour PT.

      It’s worth noting lots of tram systems still enjoyed public support when they were shuttered, often to make room for roading projects.

      It seems the central government is very much biased in favour of building roads – even in countries with good public transportation (see crazy projects like the Aqua Line in Tokyo). I wonder if there’s a reason.

  3. Its not just State Highways and Government modelling which is problematical either, the modelling that AT and its traffic consultants do for both AT and for big developments, seem to definitely get it consistently wrong with regards local traffic effects as well. Probably because they don’t model PT aspects very well – either as being impacted by traffic or by how willing people are to switch modes if they see a benefit.

    This same “optimism bias” also permeates the national level modelling, because they seem to assume that once you’re a driver – you’re always a driver from then on.
    And once freight hits the roads, it always goes that way. Whereas the real world is a lot more flexible and subtle than that.

    Our traffic modelling is little better than studying the entrails of dead animals as the ancient Greeks did to determine the future.

    Actually now I think about it, maybe the Greek knew something we’ve forgotten and studying dead animal entrails would provide more insight than what these models do?

    1. In 100 years we will look back at our “scientific models” and find they have the same results as animal entrails reading: an excuse for governments to do what they want with our money

    2. and perhaps it’s just difficult? I think modelling is better than studying animal entrails.

      What I think is a bad look is that no-one from MoT and the NZTA seem to have fronted up publicly to take responsibility and/or acknowledge the aforementioned modelling efforts. If NZTA were a private company, which was basing its capital investment programme on these numbers, then the board would probably have been sacked by now. And several consultants would have probably been quietly shown the door too …

      You only have to look at the energy gentailers to see how they have trimmed back their capital investment in response to soft demand. I think it’s ironic that the government partially privatized the gentailers to expose them to greater fiscal discpline, while the MoT and NZTA are simultaneously encouraged to go beserk (nice randy scandy word that one).

      I’m starting to wonder whether the best strategy is to turn NZTA into a new SOE, bundle in KiwiRail, and expect them to make a return on capital. Boom boom boom. Put that in your tail pipe and smoke it.

      1. yes good idea. They did that in Italy in the 90s. Sold the motorway network to private capital (Benetton being the biggest). Result: no more investment, increase in tolls.

        1. I think transport networks are too monopolistic to privatise.

          Instead the best we can expect is that they are run efficiently, and I think you can achieve that while retaining public ownership/strategic input.

        2. Too monopolistic? That hasnt stopped us and others doing it in other areas. Electricity networks are just as monopolistic which we have privatised in NZ (bar transpower which is run as an SOE so same diff). Similarly water networks have been privatised elsewhere (e.g. the UK).

          IMHO the problem of private monopolies has essentially been solved – you need regulated tarrifs and therefore a regulator.

          Road networks (or at least state highways) could easily be run as an SOE, this doesnt require privatisation but it would be little different to a private model. But it would be vastly different to the current model.

        3. Edit – oops I see you have said turn NZTA into an SOE above. Agreed, but once it is an SOE in theory there should be very little difference between that and a privatised NZTA.

        4. not sure I agree that electricity networks are “as monopolistic” as transport networks. I think it depends on what component you are talking about. Electricity networks comprise of four core components: Generation, transmission, distribution, and retail (often by same companies who generate).

          Generation is private; transmission is public; distribution is, well, a weird mix of both; and retail is private.

          Worth noting that New Zealand’s journey to this point with regards to the electricity system has been a 20 year process of careful market design and policy evaluation. Same with the telco sector, at least after the initial somewhat rash hock-off.

          Transport networks are in some ways more simple while also being more complex. They’re simple insofar as they simple require a network and a retail model. One of the key differences, however, is that roads provide a conduit for the delivery of many other types of utilities and services. Some of which were put in a long time ago such that we now don’t know where they are. Some of which have not historically been paying the road provider for their access (albeit subterranean) to the road network. You’d have to think carefully, for example, about how the transport network provider interacted with other public/private operators.

          So I’d be very careful about privitizating the road network, because if it’s not well thought through you could get some perverse effects, especially with regards to transaction costs. And costs being shoved off onto other utility providers simply because they have a high sunk investment in their existing asset, which just happens to use the road corridor because that’s the way it was done back then.

          But heading in the general direction of a more fiscally responsible NZTA would be something I’d definitely support, and I think the first step is to create an SOE that is arms-length from the gummint.

        5. Stu,

          I was referring to distribution which is effectively privatised (yes in Auckland the AECT is kind of public but all it does is distribute dividends, Vector is for all intents and purposes a private (public) company). Distribution (and transmission) are monopolistic networks just the same as a road network.

          Agreed utilities utilising road reserves complicates things. There are similar issues (in reverse) for transmission and distribution networks which cross private land – these can be dealt with. Not to mention water and wastewater networks (which is what I assume you are in part referring to) which already to cross private land so there are existing mechanisms in place for dealing with this. There would be no issue with, when setting up a road SOE, granting easements to other utility operators and putting certain covenants on the titles.

          An alternative would be to not sell the land, but charge a lease.

          Basically SOEs are set up to run like a private company would, hence there would be little difference in outcomes.

          Agreed re setting up an SOE first.

        6. Gotcha.

          In terms of convenants/easements etc: Yes there’s existing legal mechanisms in place, but the work involved really would be enormous. So I’d be a little wary of transaction costs.

          But yes, SOE would enable you to get all these things sorted first and then stop, re-gather, and work out what to do from there.

      2. “I’m starting to wonder whether the best strategy is to turn NZTA into a new SOE, bundle in KiwiRail, and expect them to make a return on capital”

        But, how do you measure that “return on capital”, and who gets to measure it?

        Therein surely, lies the rub?

        If we have a notional “capital return” as a key measurement of “success” of your new SOE, then surely its simply a theoretical return on money spent, based on estimates of time (thus money) saved. As what else can you use to measure it?

        So how do we estimate those savings? why we use modelling!

        Umm, isn’t that modelling part of the problem we’re trying to avoid/solve here?
        So how does replacing flawed modelling process with a nominal return calculated from the same flawed models get any further down the road?

        And do we trust NZTA to do the calculations of the returns, bit like having the fox guard the henhouse isn’t it?

        BTW: All for including KiwiRail into NZTA’s ambit, provided they take a mode neutral approach to their decision making – and have proper multi-modal modelling software so that it can handle the transfer of freight from road to rail and v.v. as and when needed. Because right now their models will show that “road is best” for all freight, which hardly helps KR – or NZ Inc.

        1. return on capital would be measured just like the Government does with other SOE’s.

          Normally not based on “money spent” but instead on the value of the asset under management. in NZTA’s case you’d just have to value the highway network. One of the good outcomes of such a process is that it would attach a value to the land owned by NZTA, such that they had an incentive to consider less land intensive transport solutions where land was valuable. Like cities. Return is determined by the government, not by NZTA.

          In terms of models, my gut response is that everyone everywhere uses “models” of some sorts, the question is whether they are very good and, if not, how they can be improved. Modelling and other research/analysis is how AirNZ decides when/where to open a new route, for example. No, I wouldn’t say abandon models altogether, as they can provide useful insight that you wouldn’t get from anywhere else.

        2. The recent KiwiRail/NZ Railways Corporation split was to address KiwiRail’s very very poor return on capital when the value of land occupied was taken into account. Now that the land has been removed from KiwiRail, a different picture emerges.

          Turning NZTA into an SOE would create the same issue for land occupied by roads, and it would be interesting to see if the same solution would be adopted.

        3. yes it’s a tricky one. There’s two obvious ways this can go:
          1) Not charge a return on capital for either highways or rail; or
          2) Charge a return on capital on both.

          My instinct would be to start with #1 (i.e. fairly similar to the status quo) but set the objective of moving to #2. This might require investment/changes in pricing etc.

          Also, my instinct is that accurate charging for use of the road network, especially for 1) peak trips and 2) heavy vehicles, would leave the rail network in a much better financial position. The first would benefit passenger rail systems in Auckland/Wellington, while the latter would benefit rail freight. All in all the increase in demand for rail services should improve the bottom line. By how much I don’t know …

  4. I can’t help thinking that although “systematic” is the correct verb, since you’re describing a system of modelling, “systemic” is probably closer to the truth when discussing bias towards modelling in positive VKT growth; that is, it’s not the models’ fault that they’re forecasting high, it’s actually a bias of the entire system. After all, look at the historic bias across transport planning in this country towards roads.

    1. yeah probably worth clarifying:
      – Project appraisal seems to be more affected by the optimism bias and strategic misrepresentation researched by Flyvberg. He suggests these factors lead to a statistically significant positive bias in the demand forecasts for transport projects, while costs are under-estimated (again statistically significant).
      – Aggregate travel demands are more afflicted, I think, by omitted variable bias. This is really what the wider socio-economic and changing preferences views are getting at: There’s things not considered in the model, which are impacting on travel demands. These also seem to result in future travel demands being over-estimated.

      So two different issues, both of which happen to point in the same direction: Perhaps it’s a systematic issue?

  5. Environmental concerns such as climate change will likely lead to many people to prefer public transport to a private vehicle. It will be a while before fully electric cars become cheap enough for someone to purchase on a low budget and as public transport is becoming more efficient by the time electric cars are cheaper PT will probably be a lot more established as a preferred transport option.

    An older population is probably going to naturally want to drive less (and eventually will stop driving all together). Fully subsidised PT means it is going to be a very economically attractive option for someone on a fixed income.

    That fewer young people are rushing out to get their drivers license says to me that there is change in preferences going on. When I was 15 almost everyone was getting their license as soon as they could possibly manage it. Almost to the point if you didn’t rush out and sit your learners within a couple of days of your birthday you were a social reject.

    1. What percentage of overall MOT revenue are petrol and diesel taxes? Seems to me that with the change to all-electric, that revenue source is going to dry up. I wonder why there is not more made of this? If I were a senior road engineer or management type, I’d be mightily alarmed that the new disruptive electric technology is going to put a serious dent in the economics of roading.

      1. Diesel vehicles pay road user charges based on distance travelled and type of vehicle. Eventually EVs will have to be moved to this or a similar system. That it hasn’t happened yet I think reinforces my point that EVs aren’t expected to make up a significant portion of the vehicle fleet for a while yet.

        1. The MOT spin is that electric car (and truck) technology is imminent…indeed NZ may become an early adopter. MOT can’t have it both ways….either NZ does go early to the new technology with reduced revenue for roading, or electric technology is a much longer term and uncertain thing, in which case the spin is clearly demonstrated for what it is.

          RUCs may be weight and distance based, but there are still petrol taxes being used specifically to fund current roads. Excise is 50 cents in the litre (according to different reports), and might generate an estimated $2 billion a year. That is a big hole to fill.

        2. How quickly NZ adopts waits to be seen. Some reasons why I think it won’t be too quick is:
          1) That presently there is little to no infrastructure to support EVs,
          2) Many people can’t afford to buy a new vehicle and buy second-hand
          3) Concerns over battery life will mean that 2nd-hand EVs will probably compete poorly against cheap 2nd-hand petrol imports.
          4) The average age of NZ cars is quite high so even if all new cars going on sale tomorrow were EVs it would still take a while for them to saturate the fleet.

          However there is no reason why RUC can’t raise an equivalent amount of revenue to petrol taxes. $0.50 per litre at 8-10 litres per 100km is $4-$5 per 100km or $40-$50 per 1000km. RUC on a small vehicle under 3.5 tonnes is $62 per 1000km incl gst ($53.91 excl gst).

        3. Yes. Points 2 + 4 are the big ones, and are related. NZ is a fleet new car market, and a private second hand one. Getting fleets into EVs is the way to do it. Obviously gov could lead this. But they don’t. Also fleets often run high mileage so the opex savings are comparatively higher. You’d think that CFOs would be keen, but only, of course, if they are prepared to think differently…

    2. Environmental concerns such as climate change will likely lead to many people to prefer public transport to a private vehicle.

      I would be very surprised by that. I have never heard of anyone riding their bike because it’s ‘better for the environment’.

      More likely the reason for any switch will be ‘time’. Currently even in the worst of traffic, taking the car will often be much faster than taking the bus. Think 15 minutes in free-flowing traffic vs 40 minutes in horrible congestion vs 1 hour on a bus. Cheaper PT will not make any difference if it doesn’t get people where they want to go.

      So what is changing the preference of more and more people away from cars? Maybe this pipe dream of “this final motorway project which will finally solve congestion” is dying out. Maybe less people still believe congestion can be ‘solved’. Maybe for more and more people, public transport will actually be a faster choice than cars.

      1. I agree time is a major factor. For me, at anywhere near peak times it is always faster for me to travel by public transport than to drive. However the environment is also important to me, and even at non-peak times, when it may be quicker to drive, I prefer to take public transport for that reason.

      2. Roeland – “I have never heard of anyone riding their bike because it’s ‘better for the environment’” – I think you need to broaden your circle of acquaintances: I could introduce you to quite a few such people (like me, for example).

        1. That’s perfectly possible you know a few. But don’t believe, for one second, that they are more than a very small minority. Wishing otherwise doesn’t make it so.

          How absurdly hostile is Auckland to cyclists? And to pedestrians for that matter? Would that situation persist if the average Joe would care even the smallest bit? Well, I don’t think so.

          Yes, the environment is a valid concern. Switching from commuting by car to commuting by bicycle is a good way to cast your vote against deep sea drilling. But I also expect trying to sell ditching the car to the general public because it’s good for the environment, will be a total failure.

  6. The graphs of the UK and US along with NZ all show the same trend we peaked not long after the turn of the century, the geology of oil could be at play, the graphs match oil production and a lower EROEI.

    It seems the MOT use wishful thinking to write these projections with no appreciation of what runs our transport.

  7. Perhaps that VKT graph includes the future impact of driverless cars. Imagine you currently travel A to B. In future the car is at C so it travels C to A, takes you A to B then the car goes from B back to C. Later to go home to A the car has to do the opposite route so 2 trips become 6 because Google thought that was a good idea. Maybe they should stick to being a search website.

    1. So instead of single occupant vehicles creating congestion problems we will have large numbers of zero occupant vehicles. Average vehicle occupancy could in fact go down rather than up!

    2. That would depend on whether the car has to always go back to a particular location to be stored. It may be able to optimise and go the nearest car storage to B after it’s first trip, and then be used by someone else nearby.

      This would of course result in some amount of tidal flow, cars accumulating at certain nodes during the day, but this could be accounted for with variable pricing. If there is a car near A and space to store it near B and no one else wants to do this trip it’s relatively cheap. If there is higher demand for this trip and/or it is necessary to get a car to come from and return to C as you describe then it costs more and the user maybe decides to either delay their trip, not do it at all or catch public transport instead.

    3. From talking to some in the industry this is one of the big unknowns and concerns. At the upper end it could dramatically increase road use which will mean peak conditions in all directions.

  8. “Vehicle substitutes, such as air travel…”

    I wonder how much of a factor this is in explaining plateauing VKT – especially increasing flying for leisure trips. Perhaps we’re not travelling less distance overall – but using cars less to do the travelling. The flying to Queenstown vs. getting in the car holiday…

    Certainly from personal experience, there’s the difficult-to-escape contradiction (when it comes to sustainable transport) of cycling and walking for everyday trips, but flying ever more frequently for long-distance travel.

    Some emerging evidence that non-motorised urban households are trading off reduced car-based mobility for increased flying:

    While non-motorised Helsinki households had slightly lower overall transport GHG emissions, their emissions from flying were far higher than for motorised households (other factors like income remaining constant).

    1. I think that’s almost certainly true. Flying is a fraction of the real cost it was 20 years ago, and flying to Queenstown is more attractive for many than driving to Whangarei. Similarly, business travel has shifted from driving to flying in many cases.

      1. Don’t discount urbanisation either. Especially in Auckland, even though the city has sprawled it has intensified 3 to 4 times as much over the last 20-30 years. Growth has been 70-75% within existing urban area. Driving has become less effective over this period within the city. This is what people complain about as congestion. It is a natural function of Auckland’s growth into a city. No road building nor attempts to limit further intensification will reverse this. Driving is just so spatially inefficient.

        If it was just petrol price then PT uptake would have bombed recently. When petrol price goes back up, and of course it will, the current supply/demand imbalance will correct, then watch what happens. In fact AT’s PT ops are very fortunate to have had this recent petrol price drop to take some of the growth pressure off PT demand. It could be even more intense. It has probably help flatten the demand curve… But it will almost certainly continue and could steepen well before the CRL or LR are built and functioning.

        1. Density has a second effect in that it will also reduce trip lengths. Even if everyone still takes the same number of trips to the same type of destinations, and the same fraction of people drive, density means destinations will be closer, both by having businesses and services sprinkled more often through the city, but more generally, any random two points in the city will be closer together.

        2. ‘If it was just petrol price then PT uptake would have bombed recently. When petrol price goes back up, and of course it will, the current supply/demand imbalance will correct, then watch what happens. In fact AT’s PT ops are very fortunate to have had this recent petrol price drop to take some of the growth pressure off PT demand. It could be even more intense. It has probably help flatten the demand curve… But it will almost certainly continue and could steepen well before the CRL or LR are built and functioning.’

          PT wins either way, If the oil price stays low more oil companies go broke and we have rationing in a couple of years, now wouldn’t that remove the blinkers of the MOT eyes.

        3. Well that came out wrong, the first paragraph was supposed to show as a copy from Patrick Reynolds post, so how do you highlight a copied paragraph ?

    2. I’m sure that air travel is replacing vehicle travel.

      But without having read the paper itself I’m very sceptical of the link between density and air travel identified in that paper, as it seems to be a cross-sectional study. Hence it would seem to be be highly sensitive to self-selection bias, i.e. the types of people who like to live in dense areas also happen to be the types of people who like to fly. Reducing density wouldn’t mean these people would fly less – they’d just drive more while flying the same as they did before. And vice versa: Take a household who doesn’t fly very much and move them into a denser area and they probably won’t fly any more than they did before/

      Basically, that sort of analysis seems to risk of quantifying sorting effects more than anything else.

    3. I can see you dilemma Karl but I have no such problem as I am happy driving and flying. “There is only one way to achieve happiness on this terrestrial ball, and that is to have either a clear conscience or none at all.” Ogden Nash

  9. As a disillusioned modeller I really wanted to make some points about transport models. First models are only any use if it is easier or more efficient to estimate the inputs rather than the outputs. Most transport models fail that test. In my view it would be easier to guess future traffic flows or mode use than it is to guess future numbers of jobs and population and car ownership and income and every other input commonly used. Most modellers avoid thinking about that problem and just input as gospel whatever someone tells them. Second most models dont even give you outputs that are very useful. Microsimulation is in vogue and that gives you a different answer each time you run it. I mean WTF use is that? Thirdly the results are always polished by the operator. If it gives something they didnt expect they look for an input error and fix the model until it gives the ‘right’ answer. And fourth virtually all models fail the Lucas critique. They don’t use inputs that are structural so we end up with traffic models that always show growth and PT models that never do until years of observation prove them totally wrong.

    1. What did people do before modelling? Seems that more observation and extrapolation of that data over shorter timeframes would be more useful?

  10. “As for the CRL, I think it’s likely to be a good project because of 1) patronage growth on the rail network, 2) Auckland’s growth as a whole, 3) the explosive growth in the city centre (both in terms of population and retail), and 4) wider trends in transport and land use policy, e.g. time-of-use road pricing and removing minimum parking requirements.”

    I’m not sure if time-of-use road pricing would support or undermine the case for the CRL. The CCFAS (which everyone seems to agree is flawed), determined that sufficient bus expansion was not possible due to capacity constraints, and so the CRL was preferred. However it also assumed 50% more people would be accessing the CBD than now by car. If we had market clearing road pricing, bus capacity would be practically unlimited on the basis that buses (carrying 50-100 people) would be able to outbid almost all private vehicles for road space. i.e. Assuming a fair value price differential between a bus and car is 3, for only $2 per bus passenger, the market price would be around $50 a car. I cant imagine many car drivers willing to pay that, for example.

      1. I guess we could clear all competing road use for the efficiency of buses and ‘force’ everyone onto them, or we could use the magic high capacity and uninterrupted RoW of underground rail and retain a level of bus and general vehicle access to the city as well…? I suppose it just depends on how obsessed we are with finding some way to not use the obvious and available solution?

        1. I would argue that having unpriced congested roads forces people off buses, not the other way around.

          But I wasn’t trying to argue for one case over the other, just assessing what the impact of road pricing would be on the viability of the CRL if implemented. Both options are available. To me pricing roads is as obvious as it gets. We look pitifully at photos of people in communist countries lining up for bread, but we do exactly that for road use!

        2. Mathew I agree. And road pricing would be positive for all effective alternatives. And I think GPS gives us the way to do it efficiently and with fewer unintended consequences. Cordon or mway pricing is likely to create unwanted barrier effects, but GPS time-of-day pricing on all roads as a replacement of petrol tax (though leaving a carbon price) wouldn’t have these effects.

    1. Except that even in the situation where buses have complete use of the road – like was proposed for Wellesley – they still said there was bus congestion issues.

      1. But that is only one road of many in the city. They simply didn’t look at a scenario where market clearing road pricing lead to a congestion free equilibrium between buses and cars.

        1. it’s an interesting debate.

          The impacts of road pricing may favour bus over rail because it frees up and the roads and therefore allows the former to operate faster. Road pricing is also likely to impact most negatively on the demand for short vehicle trips, which are more suited to buses.

          On the other hand, if the road pricing scheme tended to target the highways leading into the Auckland isthmus then rail may be a better substitute. This is especially true in the south, where the southern line runs largely in parallel to the motorway.

          So I really don’t know whether rail or bus will gain the most from road pricing.

          What is fairly clear (at least to me) is that road pricing increases the demand for PT, especially during peak times, and as such is likely to improve the business case for the CRL.

          And while I understand the desire to consider a bus only alternative to the CRL, my gut feeling is that in the presence of road pricing the demand for PT will be sufficiently high so as to warrant investment in both the CRL and a high-quality bus solution.

          In terms of the latter, remember that we don’t yet have the NW busway online, which will drop more buses into the city. So while CCFAS had its challenges with regards to modelling and assumptions etc, it’s not clear to me that it drew the wrong conclusions.

  11. “More recently, this post on the SH20 Manukau Harbour Crossing found it was carrying approximately 45% less traffic than projected 10 years after it was complete.”
    Considering it was completed in 2010 I don’t quite see how you get 10 years? That duplicate bridge was long needed as it could be a nightmare getting to the airport (something which is time sensitive). Yes rail to the airport is still the goal of course.

    1. I think the 10 year reference is to the forecast which, you’ll notice in the chart starts in 2004, remember these forecasts are done years in advance as they are about justifying the whole project, and it forecast the demand to precede the doubly of lane supply; bigger jams I suppose?

        1. Ok it’s just ambiguous and certainly appears to refer to the bridge completion (which is 6 years after the graph date of 2004). Would have been hard for traffic to grow between 2004 and 2010 as the existing bridge and approaches were often at capacity. If you move it all along 6 years then it does become closer to predicted (but still considerably less than predicted). IMHO it was and is needed and has improved travel to the airport in particular considerably. I just wish they would get on with proper heavy rail and stop wasting time and money with their LR wet dreams. LR has a place (within the isthmus for example) but is a poor option for long distance travel and to airports in particular.

        2. yes I agree wording was ambiguous.

          Just on the capacity constraint point you raise: I suspect this is factored into the above projections, i.e. the model would have assumed an opening date for the bridge of say 2011 and demand would have been constrained by capacity prior to that point. Hence, you can’t really explain the difference between the predicted and observed on the grounds that the observed was constrained by the lack of capacity – because the impact of capacity on demand is considered in the model (at least in the short-run).

          So … IMO it remains a good example of a bad forecast.

          In terms of heavy rail versus light rail I completely agree.

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