Over the next 15 years, taxpayers and investors will spend more than $60 trillion on the most complicated and expensive projects in the world. Despite the hype and promises made by the leaders behind those behemoths, odds are, these megaprojects — think the largest bridge and longest underwater tunnel on Earth — will run over budget, be delayed and fail to deliver what investors and taxpayers were promised. In light of this week’s election results, Stern speaker and megaprojects expert Bent Flyvbjerg has taken a closer look at one of President-elect Donald Trump’s primary campaign promises:

Now that Donald Trump has been elected US president, will work start on his proposed wall along the US/Mexican border and will it ever be completed? I think the answer to both questions is a clear no.

The plan appears poorly thought out and there are no details on how it is to be built. Like all megaprojects, it carries the inherent risk of huge cost and time overruns, and of being unfit for purpose.  Despite being built around the world for centuries, the vast majority of large infrastructure projects still suffer cost overruns.  There are no precedents for a 1,000 mile concrete wall. If you combine a lack of available experience and knowledge with very complex political, legal, financial and environmental issues, the chances of it being built to budget and time, working according to intention are virtually zero.

The finances of the proposed wall simply do not add up. Trump has suggested that construction of the wall will cost in the region of $10 billion. The likely construction costs would be much more, probably in the region of $15-$25 billion.  On top of that would be maintenance costs, which could run into the billions each year. In all likelihood, the construction would take years, surpassing Trump’s presidency and taking us into a world where issues of immigration and security, which this wall is promised to solve, may be very different from what they are now.

Flyvbjerg, a professor at Oxford University’s Saïd Business School, is the author of “Megaprojects and Risk” (Cambridge University Press, March 2013). Contact us to book Flyvbjerg to speak at your next event.

Bent Flyvbjerg’s thoughts have been re-posted here with his permission. He originally posted this piece through the University of Oxford’s Said Business School News page on November 9, 2016, which can be found here.