One of the most delay-plagued, congested airports in the world seems like the last place you would want to route lots of passengers who are simply making a connection. But that is what Delta Air Lines Inc. is doing at New York’s La Guardia Airport.

Located in the borough of Queens just a few miles from midtown Manhattan, La Guardia has long been a prime gateway into and out of New York, handing 24 million passengers a year with just two intersecting runways and overcrowded terminals, taxiways and gates. Passengers endure delays in exchange for the convenience of proximity to the city, but few would go there simply to switch flights.

Delta is now trying to change that. After acquiring a large block of landing slots and gates from US Airways Group Inc. earlier this year, Delta added more than 100 additional flights a day at La Guardia, switched some flights to larger airplanes and began building a hub