Two weeks ago, I put out a blog looking through which airports had the most domestic connecting traffic in 2018. That blog provided some interesting information about how Origin & Destination (O&D) passengers different from airport to airport. As a reminder, O&D passengers for an airport are passengers that begin or end their trip at the airport and does not include the passengers just using the airport to connect and the O&D totals can be a good proxy for how much air traffic the surrounding area is generating. While the previous blog offers a great 2018 snapshot of O&D, in this post I decided to look more deeply at historical O&D going back to 1993 when the data is first available from Bureau of Transportation Statistics DB1B database.

The first two questions I tackled were:

• Which airports have seen the most growth in the last 25 years?
• Where do the airport's rank against each other each year?

First I filtered down to the top 60 domestic airports for O&D passengers in 2018. Very happy that TTN grew roughly 17,000% since 1993, but doesn't offer a very fair comparison. The last airport to make the cut was Omaha with 4.4M O&D passengers in 2018. In terms of growth, their were 10 airports (listed below) that each grew by over 200% during the last 25 years with Charlotte (CLT) topping the list (for percentage growth) going from roughly 3.3M O&D passengers in 1993 up to 12.3M in 2018. I wanted to call out CLT's growth in particular because in my previous blog, CLT was a clear outlier in terms of the percentage of connecting passengers that funneled through it's airport compared to the size of it's O&D. That analysis, questioned why CLT continued to grow as a hub for American, but this growth gives at least one reason why American continues to grow it's operations in CLT.

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The rank in the above chart shows the how the airport's raw O&D passenger count compares to the rest of the country. Since in general total US O&D passengers has grown significantly in the past 25 years going from 580M total passengers in 1993 to 1.14B in 2018, the rank gives a look at which airports are growing faster or slower than the rest. Below is plot showing how the top 40 ranked domestic O&D airports has changed over time (hover over a line for more info). The plot below is a bit busy, hovering over a line will show airport associated with the line along with the year, raw O&D passenger numbers and rank from that year.

There hasn't been a lot of shifting at the top end of the rankings. Las Vegas did make a big move up in the 90's and even overtook LAX in the top spot for a few years right before the recession. The other big mover near the top was Denver. The were already large (13th) in 1993, but have had sustained above average growth driving them all the way into the number 2 spot in 2018. While the top has been fairly steady from about the 15th rank upward, the rest of the airports have been all sorts of a jumble, mainly because many of these airports are so close to each other in terms of raw number of passengers. A few years of high growth can move an airport up 5+ spots, while airports that saw a couple of leaner year (even if they were still growing) can drop like a rock. I've highlighted the lines of four airports (St. Louis - STL, Kansas City - MCI, Minneapolis - MSP, and Nashville - BNA) below to show an example.

Both STL (light orange) and MCI (green) have seen growth in their O&D passengers in the last 25 years growing 25% and 52%, respectively. But that growth has lagged well behind the average growth of the top sixty airports (104%). Because of this slower growth, they've both moved significantly down in their O&D ranking, with STL going from 21st to 38th and MCI from 26th to 39th.

MSP (dark orange) has seen average to above average growth over the same period which has allowed them to move up a few ranks. MSP and STL had very similar numbers in 1993, but have diverged greatly since then. In 1993, MSP had 8.8M O&D passengers (ranked 20th) and STL 8.3M. The bar chart below shows the yearly percent changes the last 25 years when both airports have seen years of growth and years of contraction following the general cycle of growth from 1993 until 2001, contraction and then renewed growth until the recession which caused more contraction until the recent five plus years of growth (see box and whisker charts near bottom of webpage). The big difference that allowed MSP to grow to over 20M O&D passengers by 2018 while STL had barely over 10M the same year, was that MSP had huge increases in passengers during the growth cycles and even though they contracted as much or more than STL during the down years, they rebounded quickly and got back to higher growth. Most recently MSP has averaged 5.7%/year growth in the last 5 years while STL's growth has only averaged 2.3%/year.

Yearly percent change in O&D traffic for STL and MSP

The last 5 years in particular have seen St. Louis drop 8 spots in the O&D rankings and MCI 5 spots. Other nearby cities grown much more, like BNA which has grown over 50% in the previous 5 years moving up 7 spots into 29th. Seeing cities like Nashville pick up more glamor routes like their British Airways London flight, I have wondered what might separate these airports from STL when their total passenger counts look very similar. Part of decisions on the larger flights are based on subsidies, but sustained growth in O&D also can help to sway a decision. BNA has added roughly the same number of raw O&D passengers to it's total in the last 3 years that STL added in a 25 year period.

We can better understand drops or rises in the rankings by looking at the range of percent changes across all airports. Below is a box and whisker plot showing the distribution of yearly percent change for the top 60 airport with STL's yearly value included as the red marker in each line. Most of the years they are below average (the black line between the blue and green rectangles) with their best years relative to the rest of the country actually coming during recession years of 2008-2010. Over the last few years STL has hovered between the bottom and second to bottom quantiles. So even though the raw percent change in the last four years have been some of STL's largest gains for O&D passengers in a decade, they are still dropping in their rankings.

Distribution of percent change in O&D traffic of largest 60 airports, showing quantiles and STL yearly values in red.

As a whole the domestic airline industry has had one of it's longest sustained runs of O&D increases in the past 2.5 decades, but that growth has not occurred evenly across the country. For example, in 2017 6 airports saw an over 10% increase in O&D traffic, but 7 airports actually lost O&D traffic. This growth (or contraction) offers a valuable context when evaluating the health of an airport. While connecting traffic is important to large airports, there are only so many flights that can be supported by boosting connecting traffic without also having O&D growth to support filling those airplanes.

Data for the O&D passenger number used in the analysis for this post was obtain from the Bureau of Transportation Statistics D1DB database. As a reminder, all values used in this analysis were for domestic O&D and did not include international itineraries.

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