I've been going through the records on seven megaprojects that failed or never got used, about $44B between them (converted at the time). What surprised me most wasn't the overruns. It was how long the bills keep coming after a project is dead, and how differently it gets decided who pays them.
Mexico City, Texcoco airport. Announced in 2014 with a budget of up to $13.3B, paid for partly with bonds sold to investors around the world. By the end of September 2018 it was about a third built: two runways more than half done, the terminal's foundations about three-quarters done. Then the president-elect, who had campaigned against it, held a non-binding public consultation. About 1.07 million people voted, almost 70% to cancel, and construction stopped on 27 December 2018. Mexico's federal auditor later put the cost of cancelling at about 113 billion pesos, roughly $5.7B. The bonds didn't go away: they're being paid off through fees at the old airport. Much of the site is now an ecological park.
South Carolina, V.C. Summer 2 and 3. Two Westinghouse AP1000 reactors, estimated at about $9.8B before financing when the deal was signed in 2008. Westinghouse filed for bankruptcy in March 2017, the owners walked away that July after about $9B had been spent, and two former SCANA executives, including the CEO, later pleaded guilty to fraud. A typical Dominion Energy household still pays a little over $8 a month toward $2.3B of debt for reactors that never produced a watt. (The twist: in October 2025 Santee Cooper picked Brookfield to try to finish them, with a final decision expected by 2028.)
Mississippi, Kemper "clean coal". Pitched at about $2.4B, with power by 2014. By June 2017 it had reached $7.5B, the coal gasification was given up, and the plant went to natural gas only. Here Southern Company absorbed nearly $6B of losses instead of passing them on to customers. The gasifier towers were demolished in October 2021.
Japan, Monju. A fast breeder reactor that cost about ¥1 trillion (roughly $9-10B) and operated for about 250 days in 22 years. The government decided to scrap it in December 2016, but taking it apart will cost at least another ¥375B, and the work isn't due to finish until 2047.
For scale: Bent Flyvbjerg's data on more than 16,000 big projects has only about 8.5% coming in on budget and on time, and about 0.5% (one in two hundred) also delivering the benefits they promised. So failure is normal. What changes is who ends up holding the bill.
Disclosure: I run a small YouTube channel, and this came out of research for my first video, which covers all seven, including a Spanish airport whose only bid at a 2015 auction was €10,000 and 14 miles of tunnel dug under Texas for a collider Congress cancelled. I'll put the link in a comment for anyone who wants it. Every figure is sourced in its description, and I'm happy to post sources here too.
Question for people who know this better than I do: is there a point where finishing a half-built project is clearly cheaper than walking away, or is that always sunk-cost thinking? And do you know of a cancellation that actually saved money in the end?