Across Europe, governments are spending billions of dollars to update public transport and improve energy provision. Many of these projects are complex feats of engineering, constructing bigger, longer, and deeper infrastructure, the likes of which have never been seen before.

But Rome wasn't built in a day, as the saying goes, and these massive megaprojects come with outsized price tags that often grow well beyond their original budgets.

Read on to find out discover where the biggest projects are underway in Europe, ranked from least to most expensive, and find out whether they'll be delivered on time and to budget. Spoiler alert: lots won't be...

All dollar amounts in US dollars.