At least by one metric, O'Hare has pipped Atlanta and gotten back to the top of the league table for total annual aviation operations:
O’Hare saw 903,747 flights in 2018, up 4.2 percent compared with the previous year, while Atlanta hosted 895,502 flights, up 1.8 percent, the FAA said. Los Angeles, Dallas/Fort Worth and Denver were in third, fourth and fifth place, respectively.
O’Hare also handled more than 83.4 million passengers last year, a 4.5 percent increase over 2017, according to the Chicago Department of Aviation. Both O’Hare and Midway Airport together saw more than 105 million passengers, a new record, the city said.
Hartsfield-Jackson Atlanta International Airport is still No. 1 in terms of passenger volume, and has held the crown of world’s busiest airport by that measure for 20 years. But a travel industry analyst said the new numbers are “excellent news” for Chicago, which is embarking on an $8.5 billion O’Hare modernization.
The article implies to big factors in the statistic: first, O'Hare now has six parallel runways instead of six intersecting ones, meaning traffic can flow much more easily. But second, American and United rely more on smaller, sub-50-seat airplanes than Delta does, which means more operations but fewer enplanements. So, it's a mixed bag, good for Chicago in some ways but not great for travelers at O'Hare.