Austin Goolsbee writes in Slate.com:
Mayer and Sinai’s study also identified the real culprit: the deliberate overscheduling of flights at peak periods by major airlines trying to increase the amount of connecting traffic at their hub airports. Major airlines like United, Delta, and American use a hub-and-spoke model as a way to offer consumers more flight choices and to save money by centralizing operations. Most of the traffic they send through a hub is on the way to somewhere else. (Low-cost carriers, on the other hand, typically carry passengers from one point to another without offering many connections.) Overscheduling at the hubs can’t explain all delays–weather and maintenance problems also contribute. But nationally, about 75 percent of flights go in or out of hub airports, making overscheduling the most important factor…
To cut down on delays, all Continental and American need to do at Newark and O’Hare respectively is to spread flights throughout the day. Continental does just that at O’Hare, because that airport isn’t its hub. Without many connecting passengers to worry about, the airline studiously avoids the congested departure periods. But the hub carriers would lose passengers and money if they did this. Spreading out flights would leave some connecting passengers with long layovers, and everyone in the travel business knows that people won’t pay as much for those tickets. Most people have a hard time figuring out which flights are leaving at overscheduled times, so they tend to avoid tickets that already have long delays built into them.
How can you avoid getting stuck on a late-leaving flight out of O’Hare? You’ve got three alternatives. If you are flying on a dominant carrier out of its hub, you can try to fly at a quiet time of day. To figure out when that is, you can download the airline’s timetable from its Web site to check when flights to other cities are scheduled to leave. You could also fly on an airline that doesn’t use O’Hare as a hub or on a low-cost carrier, both of which tend to avoid the crowded periods. Your last option is to take a deep breath and thank your airline for having so many connecting flights for you. If you’re delayed, you’re just paying the price of access to all those convenient choices.
Here is the full analysis.