Hartsfield-Jackson International begins a new era with the opening of its international terminal a week from Wednesday, but it’s hardly the final expansion planned for the world’s busiest airport.

A wide range of other airport improvements and expansions are under way, being planned or still possible. They include a revamp of roads leading to the main terminal, a runway extension and concourse expansions, as well as the possibility of a sixth runway and a new south gate complex.

“We’re building for the future,” Hartsfield-Jackson General Manager Louis Miller said.

The airport’s biggest tenant, Delta Air Lines, also is looking ahead. CEO Richard Anderson said last week the airport could also expand by adding Concourses G and H, with Delta moving its hangars in that area to former Ford plant land the airport acquired last year.

That is only an idea at this point, but many projects under way or planned are already part of the airport’s more than $6 billion capital improvement plan, laid out after a 1999 update of its master plan. The plan gave rise to a fifth runway and the international terminal, along with other major additions like the rental car center.

Airport officials recently started a new effort to update the master plan to examine what projects should be planned for the future — its first such review in 12 years.

In the background is the nagging question of a second airport. There’s none in the plans for the near future, but the idea seems never to go away entirely, perhaps because Atlanta is one of the few major American cities with only one commercial airport.

A study funded in part by the Federal Aviation Administration concluded last year that there are no feasible sites for a second airport.

Unless that changes, the focus will be back on expanding Hartsfield-Jackson. The airport, on a 4,700-acre plot bordered by the cities of Atlanta, College Park, Hapeville, East Point and Forest Park and by Fulton and Clayton counties, still has some available space and some facilities that could be moved.

Of projects already in the works, among the most noticeable will be the makeover of the approach roads to the main terminal. The aim is to eliminate “problematic lane changes” and other complications of the maze-like tangle of roads, the airport says. Work starts this summer and will be done in about two years.

The airport also is working toward an expansion of the centers of Concourses C and D to enlarge those claustrophobic areas and allow room for additional restaurants or shops. Also planned is a modernization of the airport’s aging escalators and elevators.

A $45.5 million, 500-foot extension of one of the airport’s five runways is under way, to allow enough room for large jets to take off with a full load when hot temperatures during the summer decrease air density and make it more difficult to get off the ground.

And Hartsfield-Jackson is close to finalizing a contract for modifications to gates on Concourse E and taxiway widening to accommodate the world’s largest passenger airplane, the Airbus A380, part of some $30 million in improvements to prepare for the super-jumbo jet. Korean Air plans to begin flying the A380 on its Atlanta-Seoul route starting Jan. 13, 2013.

“It’s a very dynamic, ever-changing place,” said Nick Parker, who is working on the master plan at Hartsfield-Jackson.

Where does all the money come from? Airport work is funded through a combination of passenger facility charges, airline lease and landing fee payments, revenue from airport operations like concessions and parking, and federal grants. The revenue streams are often used to back bonds or other financing.

Some improvements are aimed at adding passenger conveniences. The airport is installing huge interactive touch-screen directories at the international terminal in its new Concourse F gate area and expects to eventually roll those out in the main terminal and other concourses. Also planned is an online parking reservation system.

Miller hopes to eventually open travel plazas near the airport with amenities such as gas stations and eateries.

One of the perks most requested by travelers has been free Wi-Fi, which is offered at many other major airports.

Miller plans a revamp of Hartsfield-Jackson’s fee-based Wi-Fi offerings through advertising or branding partnerships, adding, “I’d like to see [the fee] get down to nothing” eventually.

More than 92 million passengers used Hartsfield-Jackson in 2011, and the FAA forecasts more than 100 million passengers using the Atlanta airport in 2015, and as many as 188 million passengers in 2040. The master plan update seeks to answer how Hartsfield-Jackson could handle such an increase.

The airport could need more gates or concourses, perhaps another runway, additional parking and other development.

But some of those additions — particularly a sixth runway, which was discussed but dropped when the fifth was added — can create conflict with communities surrounding the airport.

The airport last fall struck a contract worth up to $3 million in the first year with aviation consulting firm Ricondo & Associates to do the master plan update over about two years. The airport plans to eventually hold public input sessions.

Beyond the airport’s borders, the international terminal was expected to drive more commercial development in the area east of the airport. But such development has been in wait-and-see mode after the sluggish economic conditions of the past few years.

While some airports like Washington Dulles have worked to attract Fortune 500 companies and other commercial activity to areas near the airport, at Hartsfield-Jackson, “there’s not nearly the quality of development you see around other airports,” planning director Tom Nissalke acknowledged during a master plan session with the Atlanta Regional Commission.

Meanwhile, many other major U.S. airports continue to expand and change, consultant and former airport manager Bill Fife said.

“For a dynamic region like Atlanta’s,” he said, “being in the forefront, as opposed to having a facility that’s from the 1950s or ’60s or something, is very important.”