Passenger traffic at Burbank Bob Hope Airport rose again in April and further improvements are likely as airlines add summer service at the San Fernando Valley’s only commercial airfield.

The airport served 333,406 passengers, up 2.3 percent from April 2014. It is the third straight month the airport has seen an increase.

Southwest Airlines continued to have the highest monthly increase of the seven airlines serving the airport. It transported 253,046 passengers, up 4.2 percent, or more than 10,000 from a year earlier.

Alaska Airways was up 4.1 percent to 32,392 passengers. SeaPort Airlines, a commuter airline serving small airports in Southern California and the Central Valley, increased its passenger count to 1,557, a more than 500 percent increase after adding service to San Diego.

US Airways experienced the biggest drop, falling 12.6 percent to 14,422 passengers. United Airlines was off 11.6 percent to 17,578 passengers.

Bob Hope Airport has struggled in the past few years as flight traffic and passenger counts dwindled amid the recession, and as carriers consolidated operations at larger airports to keep planes full. But coming months could continue to see increases in passengers as four of the airlines have notified the airport they will add seasonal flights beginning this month.

This week US Airways is adding one daily nonstop to Phoenix on its Sunday through Friday schedule, while United is adding three daily flights on its weekend schedule serving Denver and San Francisco.

Starting June 7, Alaska Airways is adding to its Saturday service with one additional roundtrip flight to Portland and Seattle. Southwest will add a net of seven roundtrip flights serving Burbank.