Are Forecasts Improving?

In response to my takedown of Reason, specifically my puzzlement at the estimates of inaccuracy in traffic forecasts, alert reader Morten Skou Nicolaisen sent me several papers on the subject. While there is past research about traffic shortfalls, for example this paper by Flyvbjerg (hosted on a site opposing the Honolulu rapid transit project), Flyvbjerg’s references are papers from twenty years ago, describing mostly subway projects in developing countries, but also rapid transit and light rail projects in the US built in the 1970s and 80s. Unlike Flyvbjerg, who posits that planners are lying, the authors of the papers he references have other theories: currency exchange rate swings, the challenges of underground construction, inaccurate forecasts of future economic growth, outdated traffic models based on postwar road traffic models. See section 6 of Walmsley and Pickett, and sections 3.3 and 4.2 of Fouracre, Allport, and Thomson (see also the range of costs for underground construction in developing countries in section 3.3).

The question is then whether things have improved since 1990. Since the first study to point out to cost overruns and ridership shortfalls in the US was by Pickrell, the question is whether post-Pickrell lines have the same problems, or whether there are better outcomes now, called a Pickrell effect.

The answer, as far as ridership is concerned, is very clearly that ridership shortfalls are no longer a major problem. See recent analysis by Hardy, Doh, Yuan, Zhou, and Button; see specifically figure 1. Cost overruns also seem to be in decline and are no longer big, although a multiple regression analysis finds no Pickrell effect for cost, just for ridership.

In particular, there is no comparison between projects from 30 years ago, most of which are underground, and present-day developed-world high-speed and urban rail lines.


  1. Nathanael

    In contrast, road traffic forecasts used to justify/excuse road construction seem to have routine major *over*estimates of traffic now.

    (Oil prices? Recession?)

      • Alon Levy

        Go to Upstate New York. Buffalo has a freeway that has the same traffic that the arterial it replaced had in the 1950s. Rochester’s Inner Loop is so empty drivers are going at far above the speed limit. Syracuse has so little traffic on I-81 it’s seriously considering demolition.

        And by the standards of the Dakotas, the roads in Upstate New York are like I-95.

        • Eric F

          I agree (!), at least as an observation. In fact, this is a point I often make to friends regarding vacation plans. Upstate NY, by dint of 50 years of population and business loss is actually a great place to visit in the summer. The weather is fairly temperate, and because it’s emptied out, traffic is light and things are fairly inexpensive. You can’t earn a living there for the most part, but if you want to hike, tour wineries or visit college towns, you are in clover. Some of the terrain up there is absolutely gorgeous and there is history galore.

          From a planning perspective: (1) the upstate NY road network was not built on the premise that 50 years of poor policy emanating out of Albany would trash the place. Buffalo was a pro town in 1950 for Pete’s sake! (2) There are spots even in upstate NY that could use some highway expansion, mainly for connectivity purposes.

          As for North Dakota, the standard interstate highway configuration is two lanes in each direction. There are not exactly superhighways in Bismark. I guess you could scale them back to one lane, but the safety and speed benefits to a two-lane alignment, especially in a place that gets enormous amounts of poor weather seem manifest. If I lived up there I’d probably advocate two-laning US 2 in ND/Montana as well. I’d hate to have drive that thing in the snow with trucks coming at me.

          • Adirondacker12800

            Upstaters whine endlessly about the congestion. If they have to wait two cycles of the light to make a left hand turn during “rush” minute they complain. Then complain that the state isn’t spending enough of hard earned New York City resident’s tax dollars on them.

          • Nathanael

            I am a big advocate of I-81 demolition in Syracuse. That road was scary to start with, and now I already drive Salina Street in preference. (Salina Street could use some improvements. Not widening, mind you; it just needs clearer striping and channelization to use it as a thoroughfare.)

          • Nathanael

            I will also suggest that part of the 50 years of poor planning from Albany was the policy
            *which allowed the degeneration and destruction of the upstate rail network*.

            The rail network is what kept Upstate tied to downstate and the rest of the world. The road network was no substitute, as it turned out.

          • Adirondacker12800

            Air conditioning happened. You don’t have to shovel humidity.

  2. Zmapper

    Sorta off topic: Using data from State traffic volume maps, recently I compiled most of the Interstates in the West that do not meet current traffic volume criteria (<10,000 ADT) if the route were to be under consideration today. I haven't covered any place east of the Mississippi yet, or a few states in the Southwest.

    Put another way, the Interstate system is drastically overbuilt out here. There was, and still is, no good reason to waste money on upgrading US-87 (I-25 today) in Wyoming to Interstate standards.

    • Andre Lot

      The share of trucks vs. cars on most “empty” Western Interstates is much, much higher than around big metro areas.

      A dual-carriageway highway has fatality rates 70% lower than a single-carriageway one-lane-per-direction highway with otherwise same features like full grade-separation and access control.

      You could build dual-carriageway, one-lane-per-direction highway, but keeping the other standards that make such routes safe and fast would mean just a marginal cost saving, considering the ROW is already there and was acquired when it was mostly very cheap or belonged to the BLM in Western states.

      It is because of this “anti-car, take that highway down” attitude that in both countries I’m entitled to vote I’d happily choose an otherwise unpalatable and misguided politician in terms of “social and cultural issues” over other that pay due to the cult of “force social engineering by denying infrastructure” (be it keeping roads bad to “force” people into trains, increasing price of energy to “force” people to use less of it, tax punitively online business to “save brick-and-mortar bookstores” etc.).

      • Zmapper

        Andre, I live in Northern Colorado, and sometimes I head up north to Glendo, WY to go fishing. There are very few people on I-25 north of Cheyenne. A two lane road would be plenty wide for what little traffic uses the road.

        Don’t believe me? Take the Google Street View person and place it randomly along I-25 a few times. Count how many vehicles you see in a single picture and ask yourself if the amount you see really needs a full Interstate highway. I bet you won’t find a location with more than 10 cars in it, and most likely the number of vehicles will be below five.

        I am far from anti-car, especially in rural areas, but the reality is that there was no real reason to build an Interstate when a two-lane road is all you need. Granted, it was built, and the cost of taking out one side of the road and making I-25 a two-lane road isn’t worth it.

        • Andre Lot

          I lived in Laramie so I used those highways fairly often (especially I-80 to Salt Lake City and I-25 to Denver).

          The former route that served I-25 alignment (US-87) crossed all cities as an urban road, slowing down traffic significantly. It was also non-grade-separated, a feature that is equal or more important than 2-lane-per-direction in terms of safety, Gosh, agricultural machines were allowed there once.

          My reasoning is: if you are going to build city by-passes (and hardly anyone would argue having 18-wheeler’s or large passing car traffic is good to have on urban streets), and add grade-separation, the marginal costs to add a second carriageway in urban areas is low.

          Lack of a 2nd lane per direction can affect speeds considerably even at low-traffic areas.

          Mix three elements (time lost from city crossing + time lost from lack of passing lane + time lost from lower speed limit) and suddenly a Denver-Billings drive stops being an 10h-10h30 driving journey and becomes a 16-17h trip that requires an overnight stay somewhere…

          • Alon Levy

            Do enough people need to drive from Denver to Billings, though? For rather the same reason it’s stupid to build an HSR line parallel to the Empire Builder, it’s stupid to build an expressway on every conceivable city pair. In Western Canada, for comparison, equivalent routes are not grade-separated, and so freight continues to go by rail, and people either drive to the resort towns or fly between larger cities.

          • Nathanael

            “My reasoning is: if you are going to build city by-passes (and hardly anyone would argue having 18-wheeler’s or large passing car traffic is good to have on urban streets), and add grade-separation, the marginal costs to add a second carriageway in urban areas is low.”

            You’re just dead wrong. Please look up the actual cost of wider bridges. It’s enormous.

  3. Pingback: Do Costs Run Over or Are They Underestimated? | Pedestrian Observations

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