Let me preface this post by saying I have nothing against Bent Flyvbjerg or his research. My problem is purely with how it’s used in the public media, and frequently even in other academic studies, which assume overruns take place even when they do not.
Stephen Smith sent me a link to an article in The Economist complaining about cost overruns on the California HSR Central Valley segment. The article gets its numbers wrong – for one, the original cost estimate for Merced-Bakersfield was never $6.8 billion, but instead was $7.2 billion in 2006 dollars and $8 billion in YOE dollars, according to CARRD, and as a result it portrays a 25% overrun as a 100% overrun. But the interest is not the wrong numbers, but the invocation of Flyvbjerg again.
Nowhere does the article say anything about actual construction costs – it talks about overruns, but doesn’t compare base costs. It’s too bad; Flyvbjerg himself did a cost comparison for rapid transit, on the idea that the only way to reliably estimate costs ex ante is to look at similar projects’ ex post costs. His paper has some flaws – namely, the American projects he considers are older than the European projects, and there’s no systematic attempt at controlling for percentage of the line that’s underground, both resulting in underestimating the US-Europe cost difference – but the method is sound. Unfortunately, this paper is obscure, whereas his work on cost overruns is famous.
In the case of high-speed rail, it seems to me, from pure eyeballing, that there is a difference between countries in how much costs run over, and that this correlates strongly with high construction costs. German train projects, including the one example cited by the Economist, run over a lot. French and Spanish high-speed lines do not, and also cost much less.
Of course, this by itself doesn’t mean this correlation should keep holding: up until Barcelona Line 9, originally budgeted at €1.9 billion but now up to €6.5 billion, Spanish subway lines were built within budget. France has not yet had a factor-of-3 overrun on a major project, but it might in the future, and I’m not going to bet my life that it won’t. But what this does suggest is that looking at German overruns as if they’re typical rather than extremal cases is deeply misleading.
There’s an argument to be made that California’s inability to rein in the contractors will in fact lead to German cost overruns. California HSR’s projected costs look downright reasonable, whereas rapid transit projects in the state are unusually expensive. The proposed BART to San Jose tunnel is $4 billion for 8 km – very high by general subway standards, and unheard of for a subway in low-density suburbia. Going by Flyvbjerg’s own attempts to find ex ante cost estimates that are reliable, this could be used as evidence for future cost escalations; general overruns couldn’t, not without being more specific.