Southwest is the US’s fourth-largest operator by passengers. However, as the US Department of Transportation shows that 98% of its traffic is domestic, it is the nation’s third-largest domestic carrier. Southwest carried one in five of all passengers who flew within the country.

In the 12 months to August 2025, the DOT shows that Southwest filled 77.8% of its available seats. This was obviously disproportionately driven by its enormous dominance domestically. Indeed, it filled 83% of its international capacity.

Southwest’s Routes With The Lowest Loads

Analysis of all the airline’s network between September 2024 and August 2025 shows that the following ten routes had the lowest seat load factors. As always, caution must be given when discussing this topic.

Loads are just one performance measure, and a broader context is usually important. For example, several of the markets were very new: three started between June and August 2025. While it might therefore be a tad unfair to dismiss them, the initial very low loads were not encouraging.

To make the list fairer, only routes with 900 or more passengers are included. Doing so indicates that Colorado Springs to the ever-popular Cancun had the lowest load, filling a ridiculously low 35.7% of seats. It was Colorado Springs’ first international service and its longest link. According to Cirium Diio data, just nine round-trip flights existed between June 7 and August 2. A tiny market, it filled just 918 of its 2,574 seats. It is due to return in December.

Four Of The Routes Are Within Hawaii

Hawaii has been part of Southwest’s map since 2019. In the 12 months to August 2025, the US DOT shows it carried 4.0 million passengers to, from, and within the state. Hawaii accounted for just over 2.4% of the carrier’s total traffic volume.

Its overall Hawaii load was 89.4%, with more services from California coming. However, its intrastate operation was far worse. It only filled 51.9% of capacity. Many of the interisland routes were heavily trafficked, but did poorly for loads. That is despite significant discounts helping Southwest to compete more effectively with Hawaiian/Alaska Airlines, which has far higher frequencies.

In all, Southwest carried 1.8 million passengers within Hawaii. It carried around one in four passengers. Despite the generally poor loads, Southwest’s intrastate traffic was more or less unchanged compared to the prior 12 months. However, as capacity reduced by 8%, its load factor rose—but only from 47.0% to 51.9%. Are Southwest’s inter-Hawaii operations really of strategic importance, or will more significant cuts materialize?

This Airport Had Southwest’s Lowest Load Factor

Between September 2024 and August 2025, Southwest flew to 117 airports. Of these, the DOT indicates that Havana had the lowest load factor overall. Just 51.7% of seats to/from the Cuban capital were filled. Its sole remaining route was Tampa, with 129,725 round-trip passengers. Unsurprisingly, Southwest pulled out of Havana—and Cuba—in August 2025.

Of the airports that remain served, Hito had the next-worst result. Served since January 2020, it filled only 61.6% of seats in the examined year. It has only ever flown from Honolulu. This very short route, which covers 188 nautical miles (348 km) each way, was certainly popular: it carried 397,900 passengers. But way too much capacity was available.