The U.S. DOT O&D reports the Distance as the average great circle distance in miles at the ticket-level, trip-level, and segment-level granularity.
At the ticket-level, this will be the average across all aggregated tickets for the total great circle distance for each True Origin-to-Destination trip on the ticket summed together.
At the trip-level, this will be the average across all aggregated trips for the total great circle distance from the Trip Origin to the Trip Destination.
Furthermore, at the segment-level, the distance will be the average across all aggregated segments for the great circle distance from the flight Origin to the flight Destination.
Please note that the ticket-level distance is the sum of the distance of each trip on the ticket, but the trip-level distance is not the sum of the distance of each segment of the trip, but is instead a straight-line great circle distance from the Trip Origin to the Trip Destination.