Driven by this post, out of curiosity I started looking at the price tag of some mega-projects around the world. Interestingly, the most expensive ones are almost always highway systems. Can someone briefly explain why? I'm my naive view it's mostly asphalt and terrain work.
Anything that involves digging holes in the ground is enormously expensive. If you take house building as an example, 25-30% of the cost is the foundations - digging it out then filling them with concrete. It’s labour, fuel, and material, intensive work.
Sometimes when they dig into the ground they find something unpredictable e.g. contaminated soil which can result in a major cost blowout, a legal fight between government and contractor and then unplanned delays which further increases costs.