STOP me if you've heard this one before: a small city begs a central government for money to upgrade its tiny, underused airport. If only the airport had nicer facilities, the city's politicians claim, more people would use it. The central government, bowing to political expediency and citing rosy traffic projections, gives in. The airport is shiny, new—and mostly empty.

This story has played out all over Europe in recent years, according to a new report by the European Court of Auditors. The report, titled "EU-funded airport infrastructures: poor value for money", found that:

too many airports (which were often in close proximity to each other) were funded and in many cases the EU‑funded infrastructures were oversized. Only half of the audited airports succeeded in increasing their passenger numbers and improvements in customer service were either not measured or not evidenced.

The auditors examined 20 airports in Estonia, Greece, Spain, Italy and Poland that received a combined €666m ($817m) in EU funding. Seven of those airports are still not profitable.

Obviously it would be unreasonable to expect governments to fund the right infrastructure projects 100% of the time. But that's exactly why reports like this one are needed. Air travel is projected to continue to increase in the EU for the foreseeable future. But some of the airports the EU bankrolled, according to the report, were too close together, and at nine of the airports, at least one of the big improvements European taxpayers paid for "were not needed at all". That waste accounted for about 28% of the €666m the auditors examined.

Some of the projects, however, were easy for the auditors to justify. Some cost just a few euro per additional passenger served. The lesson, as the report notes, is that the EU and other large central governments should carefully analyse whether airport infrastructure investments will be worth the cost—and pay particular attention to whether the airport is financially sustainable. It seems especially bizarre to pour money into a failing enterprise, but in some cases that's exactly what the EU did. The whole report is fascinating, and full of colourful maps and charts. If you're interested, you can read it here.