The shops are brimming with books, shoes, wine, gadgets and hot coffee. Serpentine-style benches are awaiting the first passengers.

So are ultra-modern security screening machines with the ability to X-ray liquids inside plastic bottles that travelers carry onto airplanes.

Philadelphia International Airport's $300 million renovation and expansion to Terminals D and E is to open to passengers today. It is the airport's largest construction project since the International Terminal opened in 2003.

Just in time for returning holiday travelers, the 204,000-square-foot "connector" building between D and E has a 14-lane passenger security checkpoint, a mall with 10 shops, and a view of the airfield.

By spring, there will be new automated baggage sorting and expanded bag-claim areas, and before the end of 2009, there will be additional gates for the airport's second-busiest carrier, Southwest Airlines.

The improvements allow passengers to walk from Terminal A - where international flights come and go - all the way to Terminal E without having to go through security screening more than once.

The Terminal E concourse - home to Southwest and Northwest Airlines - has been isolated until now behind its own security checkpoint, with cramped, jury-rigged security lanes. About a fourth of Philadelphia passengers depart from or arrive in D and E.

The renovations do for Southwest, AirTran, United, Northwest, Continental and Air Canada - all of which fly out of D and E - what a $139 million makeover to Terminals B and C did in 1998 for US Airways, Philadelphia's dominant airline.

Starting today, passengers flying out of D and E will be ticketed in the lobby and head up escalators, past a glass wall of art, to the combined security area. (Previously there were four security lanes in D and four in E.)

Airport officials wanted to open the area before Christmas, but details of securing the new building - wedged between two busy terminals - took longer than expected.

In all, 56 doors were electronically keyed to operate under stringent Transportation Security Administration requirements.

Contractors spent up to two hours testing each door to make sure it closed properly and worked with electronic card swipes, in line with government standards imposed after the Sept. 11 terrorist attacks.

"We think it might be the most advanced security checkpoint in the country," said city aviation director Charles Isdell. "There's just a whole lot of electronics. We had to make sure everything was tested and accepted by the TSA before we could give the green light."

By spring, a new system with high-technology explosives-detection machines that screen bags at a rate of 750 an hour, will be ready on a floor below the passenger screening.

From the security lanes, travelers spill onto a row of shops that flank a 90-foot-wide wall of glass overlooking the airfield. Ten shops, stocked with merchandise, are ready for customers. They include Lids, Brookstone, InMotion Entertainment DVD rentals, Borders books, Vino Volo wine bar, Taxco Sterling jewelry, Peet's Coffee & Tea, Crocs shoes, and Tech Showcase, a wireless-gadget store.

The $300 million tab for the improvements will be paid by airport revenue bonds funded by the airlines and "passenger facility charges," Isdell said.

Construction has begun at the end of Terminal E, paid for by Southwest Airlines, on a fan-shaped extension with seven gates for aircraft, along with a 350-foot curved glass wall.

A new D-E baggage-claim building with nine carousels is being built that will connect the existing D-E baggage-claim area.

Looking to the future, the airport plans to revamp Terminal F, where nearly 400 commuter and regional jet flights depart daily. That $100 million project would link Terminal F to E so passengers would be able to walk from A to F - the length of the airport - and go through security only once.

"If we find our revenues starting to decline, we can always build it in phases," Isdell said. "We're optimistic that we'll be able to build it in one single project."

The Philadelphia airport is North America's 10th busiest and handles 32 million passengers a year. The airport expects passenger traffic this year to be down 1 percent or 2 percent compared with 2007 because of the economy.

Next year, US Airways CEO Doug Parker said he expects a bounce back in air travel based on advance bookings. "We could end up being flat, or a little bit better, but probably still in the 32 million-passenger range," Isdell said.