The literature on cost overruns for infrastructure projects is rich, much more so than that for absolute costs. The best-known name in this literature is Bent Flyvbjerg, who in the early 2000s collated a number of datasets from the 1980s and 90s to produce a large enough N for analysis, demonstrating consistent, large cost overruns, especially for urban rail. Subsequently, he’s written papers on the topic, focusing on underestimation and on how agencies can prospectively estimate costs better and give accurate numbers to the public for approval. This parallels an internal trend in the US, where Don Pickrell identified cost overruns in 1990 already, using 1980s data; Pickrell’s dataset was among those analyzed by Flyvbjerg, and subsequent to Pickrell’s paper, American cost overruns decreased to an average of zero for light rail lines.

But a fundamental question remains: are cost overruns really a matter of underestimation, or a true overrun? In other words, if a project, say Grand Paris Express, is estimated to cost 22.6 billion € in 2012 (p. 7) and is up to 35.6 billion € today (p. 13), does it mean the cost was 35.6b€ all along and the 2012 analysis just failed to estimate it right? Or dos it mean the cost was 22.6b€ then, and then the budget ran over due to failures of planning that could have been avoided?

Transit agencies that just want to avoid the embarrassment of media headlines saying “they said it costs X but it costs 2X” care mostly about underestimation. This is also true of both generic project managers and political appointees, two groups that do not care about the details of how to build a subway, and think of everything in abstract terms in which a subway might as well be a box of shampoo bottles.

However, the concrete examples that I have seen or heard of for cost overruns look like overruns rather than underestimation. That is, those projects could have been done at the original cost, but planning mistakes drove the budget up, or otherwise created conditions that would enable other forces to drive the budget up.

The Netherlands: early commitment

Bert van Wee is among the world’s top researchers on cost overruns, even if he’s less well-known to the public than Flyvbjerg. He spoke to me about the problems of early commitment in Dutch planning, in which politicians commit to a project before design is finalized. Once the political decision has been made, it is easy for actors to extract surplus, because the state or city cannot walk away easily, while a 20% cost overrun is much easier to explain to the public. This problem plagued 2000s investments like HSL Zuid. To deter this, after 2009 the Netherlands passed reforms that attempt to tackle this problem, aiming to defer the formal political decision to later in the process.

This factor seems to correlate with absolute costs, if not with overruns. American planning is extremely politicized; Canadian planning is fairly politicized too, with individual subway projects identifiable as the brainchildren of specific politicians or parties; Southern European and Nordic planning is highly bureaucratized, with design driven by the civil service and politicians making yes or no decisions late in the process.

Sweden: changes in rules

According to a senior planner at Nya Tunnelbanan, the project has run over from 22.506 billion kronor in 2013 to 31.813 today, both in 2016 price levels; in US dollars, this is $2.551b/19.6 km to $3.606b/19.6 km, all underground. The reasons for the escalation come largely from tighter regulations as well as litigation:

• Safety requirements have been tightened midway through the project, requiring a service tunnel in addition to the two track tunnels, raising excavation volume almost 50%
• An environmental court ruling slowed down excavation further
• Consensus with stakeholders took longer than expected
• Excavated rock was reclassified midway through the project from useful building material to waste that must be disposed of

Focusing on underestimation is not really germane to what’s happened in Stockholm. The problem isn’t that early 2010s engineers failed to anticipate regulations that were not in force at the time. It’s that regulations were changed later. The rock removal process today actually increases greenhouse gas emissions, just because of the need to freight it away, let alone the systemwide effects on climate of making it harder to build subways.

California: scope creep and change orders

California High-Speed Rail is such a big project that its cost overruns, in multiple stages, were amply discussed in the media. The original announcements in the early 2010s, for example here, were largely about scope creep. At-grade segments turned into viaducts; above-ground segments, particularly in the Bay Area, were turned into tunnels. The reasons were mostly about agency turf battles.

Only in one case was the problem more about underestimation than overrun: the Central Valley segment had originally been planned to follow railroad rights-of-way, but had to be redesigned to have more viaducts and swerve around unserved small towns. This was bad planning, at two points: first, the original designs assumed trains could go at 350 km/h through unserved towns, which they don’t anywhere; and second, once the redesign happened, it was so rushed that land acquisition was time-consuming and acrimonious. Even then, much of the overdesign as identified by a Deutsche Bahn postmortem could have been prevented.

The second stage is more recent: the Central Valley construction contracts have long busted their budgets due to change orders. Change orders are a common problem in California, and in this case, it involved not only the change order king Tutor-Perini, but also the usually reasonable Dragados. The situation here must be ascribed to overrun rather than underestimation: a transparent process for handling changes, based on itemized costs, is an emerging best practice, known since the early 2000s to people who cared to know, and more recently seen in the economics literature for general infrastructure. That California failed to follow this practice – which, again, was available already in the late 2000s – is the source of malpractice. The original bids could have held if the process were better.

Absolute costs and cost overruns

Cost overruns are not the same as absolute costs. They are not even obviously correlated: witness the way the US eliminated most overruns on surface light rail projects in the 1990s and 2000s, to the point that projects with large overruns like the Green Line Extension are exceptional, while absolute costs have skyrocketed. But if we understand the problem to be about cost overruns from an ambitious but achievable budget rather than about underestimating a final cost that could not be improved on, then the study of the two topics is inherently intertwined.

Problems that recur in postmortems of cost overruns are not just about estimation. They’re about building better and cheaper. A bureaucratized planning process in which politicians retain the right to make yes-or-no decisions on complete design reduces cost overruns by reducing leakage and surplus extraction; the overruns such a process prevents are preventable extra costs, rather than higher initial estimates. The same is true of avoiding overbuilding, of not introducing extraneous regulations, of treating environmental questions as systemic and quantitative rather than as local under a do-no-harm principle. Even the question of change orders is more transparently about reducing absolute costs in the literature, since the overruns prevented tend to be seen in higher risk to the contractor leading to higher profit margin demands.

The upshot is that this makes the study of absolute costs easier, because we can reuse some of the literature for the related problem of cost overruns. But conceptually, it means that agencies need to be more proactive and treat early budgets as standards to be adhered to, rather than just blow up the budgets preemptively so that it’s easier to stick to them.