A runway at Hartsfield-Jackson International Airport had some unusual traffic early Saturday morning: hundreds of people running and walking a 5K.

The airport’s annual 5K on the 5th Runway brings participants onto the airfield of the world’s busiest airport in pre-dawn hours.

Hosted by Atlanta Mayor Andre Dickens, it’s touted as “one of the flattest and fastest courses in metro Atlanta,” and is also a qualifying race for The Atlanta Journal-Constitution Peachtree Road Race.

The fifth runway is closed to airplane traffic during the race, but anyone running or walking had to finish by 7:30 a.m. so it could reopen to aircraft. Jets continued to take off and land on the airport’s other runways during the race, but the fifth runway sits on the far south side of the airfield, affording runners some distance from the airplane traffic.