On June 18, 1971, America’s most iconic affordable air carrier opened for business when Southwest Airlines was officially founded. In the 55 years that have passed since the carrier began serving American travelers, it has grown into not only the largest low-cost carrier in the US but also one of the biggest airlines in the world.

As of 2026, the 15 busiest routes in the Southwest network are all major air corridors that link many major cities in the USA as well as the largest SWA bases and its busiest airports for connections. While controversial changes to its business model have begun to transform the airline once again, it remains one of America’s most popular carriers.

Southwest Airlines’ Top Destinations

Credit: Great Circle Mapper

The number one most popular route in the network, as determined from data collected over the period of March 2025 to March 2026, was found to join Denver International (DEN) to Phoenix Sky Harbor International Airport (PHX). According to the US Department of Transportation, there were 965,175 travelers transported by SWA over the 12-month time span with a load factor of 76%. Notably, that load factor is actually lower than the second busiest in the list while the volume of flyers is higher.

According to the DOT, the second most popular route in the SWA network is the airport route between San Diego International Airport (SAN) and Sacramento International Airport (SMF). There were a total of 934,163 flyers recorded on Southwest flights, with the carrier’s load factor at 80%. Rounding out the top three was the busy air bridge from Harry Reid International (LAS) in Las Vegas to SAN. The DOT reported 896,182 over the course of the year, with SWA reporting a load factor of 77.4%, also higher than its busiest route.

The 55th anniversary of SWA happens to coincide with the 250th anniversary of the USA. The airline marked the milestone with a new ‘Independence One’ livery. SWA also honored two flight attendants who have served since 1971: Deborah Stembridge and Sandra Force. The airline held a special photo op to highlight the change in FA uniforms, using Sandra’s ‘Hostess of the Month’ 1972 picture, contrasting the classic go-go boots and poncho. To top off the historic year, SWA brought a live pop-up performance to flyers at 35,000 feet as part of its Live At 35 when the Plain White T’s played “Hey There Delilah,” to a full plane of passengers in flight.

Big Changes At SWA In 2026

Credit: Southwest Airlines

It will be interesting to see how these figures change over the coming year as the airline has officially instituted a number of major changes to its business model and is expanding the network. Keeping up with the wider trend of premiumization in the air travel business, SWA is shedding its budget carrier identity primarily to compete more directly with the legacy ‘Big Three,’ United, American, and Delta Air Lines.

Below is the top 15 list with traffic figures from March 2025 to 2026, per the US DOT:

As of January 27th, the airline officially ended its open seating policy to a very mixed reaction from its loyal customer base. Despite some pushback from longtime customers, the load factors have stayed very high. Meanwhile, in May, SWA began offering flights to Anchorage Airport (ANC) in Alaska for the first time in its history.

The New Way To Fly At SWA

Credit: Southwest Airlines

One of the major changes that has been instituted at Southwest over the past year includes the shocking decision to end the ‘bags fly free policy.’ SWA now charges $35 for the first checked bag and $45 for the second bag. The combined revisions to the airline’s business model are bringing it closer to a mainline operator, with many loyal fans mourning the ‘death’ of the airline as they knew it.

The cabins of all of its planes are being reconfigured to make roughly one-third of the rows premium seats, known as ‘extra legroom.’ Booking an ELR seat automatically assigns travelers to Boarding Group 1 or 2. SWA also partnered with SpaceX to integrate Starlink Wi-Fi, aiming to equip over 300 aircraft by the end of 2026. To complement the improved inflight internet service are new device chargers and holders integrated into the Recaro seats that have been installed as part of the cabin overhauls.