The ATSlab has a new (open access) paper out on airport capacity expansion. 55 of the world’s busiest 150 airports added runways or were replaced with higher-capacity new airports between 2000 and 2016. We looked at what happened next – for example, the airports tended to add longer-haul flights than those they already had, and over half of the expanded airports either didn’t use the new capacity or rapidly became congested again over the time period we looked at.