Commercial aviation in the United States is primarily driven by traffic in and out of giant hubs, but the longest runways are not always found at the busiest airports. Runway length reflects a lot of different factors, including everything from geography, climate, aircraft performance, and airport role as much as raw passenger volume. This, at the end of the day, is why Denver International Airport (DEN) sits at the top of the list with a 16,000-foot (4,877-meter) runway strip built for hot-and-high operations.