Southwest stepping up service to Las Vegas, other markets. (Southwest Airlines Co.)

Dallas-based Southwest Airlines is expanding again. This time the carrier is adding some West Coast routes to its schedule as well as beefing up service from Las Vegas, America West Airlines' second hub.

Southwest will add two flights each from Las Vegas to Phoenix and to Los Angeles at the beginning of March. It will also add daily round-trips from Las Vegas to San Diego, Burbank and Ontario, Calif.

"It makes sense to fill slots as they become available to us," explains Karen Hayenga, a Phoenix-area marketing manager for Southwest. "We have a higher yield for short-haul flights because of our cost structure."

Southwest has about 15 daily flights from Las …