On a recent trip to New Orleans, I wondered how city size correlated with the busyness (or lack thereof) of that city’s airport. How strong is the population-to-passenger correlation and how much do other factors, like being a hub and/or being a vacation destination, impact this correlation?
To answer this question, I first compiled a list of the 20 most populous Metropolitan Statistical Areas (MSAs) (source). I modified this list to merge MSAs that overlap and/or share airports (LA + Riverside; Washington + Baltimore; and San Francisco + San Jose). I also expanded the list to include a few smaller MSAs that I thought would be interesting to look at, like Las Vegas and New Orleans.
Next, I compiled airport usage statistics for the 60 busiest airports in the US and matched them with their respective MSA (source). Specifically, I used passenger boardings in 2017 (Chicago Midway and O’Hare and Honolulu’s airport only had 2016 data available). For some cities, there is only one major airport (e.g. Boston with Logan Airport) but for others, there are multiple (e.g. New York’s EWR, LGA, and JFK). Some cities have other, smaller airports that were not included because they were not on the top 60 list and therefore were statistically less relevant.
Finally, I performed a simple linear regression in Excel and added a trend line. As the chart (and R square of 66%) show, MSA size helps explain much, but not all, of the variation in airport usage.
Cities that overperform the most, relative to their population, include Atlanta, Chicago, Miami, San Francisco, Dallas, and Denver. Cities that underperform the most include LA, Philadelphia, New Orleans, St. Louis, Tampa, San Diego, and Portland.
St. Louis’ MSA is roughly the same size as Denver’s (~2.8m) but has less than 25% the passenger boardings! Meanwhile, Denver is half the size of Houston but has more boardings!
An important variable might be whether a city has a hub airport (or multiple). However, most of the MSAs profiled, and nearly all of the largest ones, have at least 1 hub of the “Big Four” largest US airlines. These US airlines – American, Delta, Southwest, and United –account for the vast majority of domestic travel (~80%). Boston is the largest MSA that isn’t a Big Four hub (but it is a hub for JetBlue – the sixth largest US carrier) which may help explain why it underperforms relative to population. Every other MSA on the list has at least one hub except San Diego, Tampa, St. Louis, Honolulu, Portland, and New Orleans. Obviously, some hubs are more critical spokes than others (e.g., Delta’s Atlanta hub is a far bigger centerpiece in their network than American’s DCA hub is), but hub-status alone is an insufficient explainer of the remaining variation in the data.
Other factors like (new) business activity, population growth, and tourism should be considered, however on the last point, I was somewhat surprised by how several popular tourist destinations underperformed (e.g. Honolulu, New Orleans, Tampa, and San Diego).
Miami and Philadelphia are interesting to compare and contrast. Although they both serve as hubs and have a similar MSA population (~6 million), Miami has nearly three times the number of air passenger boardings (Miami includes West Palm Beach and Fort Lauderdale airports). Miami’s status as a vacation destination and gateway to Latin America probably play an important role as does Philadelphia’s sluggish recent population growth and close proximity to two larger/busier MSAs, Washington and New York.