Planes started landing and taking off Thursday morning on the 10,800-foot runway in the southern half of the airport's footprint. That will mark the end of the first phase of the O'Hare Modernization Program, a massive project that aims to address the crippling delays and maintain the airport's status as a key crossroads in the nation's transportation architecture.
"It will improve the efficiency of the national aviation system from coast to coast," Chicago Aviation Commissioner Rosemarie Andolino said at a ceremony to mark the opening.
The question now is how soon travelers will start to notice. O'Hare still ranks at or near the bottom in on-time departures. Chicago Department of Aviation officials say the runway will allow for nearly 90,000 additional flights per year while reducing delays by half.
"O'Hare's been bottled up for so long. This could lead to some exciting things, some new services," said Joseph Schwieterman, Chicago-based transportation researcher at DePaul University, adding that a low-cost carrier could even move in.
Under the project, which began in 2003, the airfield's crisscrossing runways will be reconfigured into a parallel layout that officials say would allow more aircraft to take off and land. The lattice network of runways was conceived to allow pilots to take off and land under different crosswind patterns; aircraft technology has largely eliminated that need.
When the project is complete, O'Hare will have six parallel and two crosswind runways.
The major expansion pieces yet to be completed are two parallel runways, a control tower, and an extension to an existing runway. One of those new runways and the control tower are under construction, but the city's airline partners in the mega project have yet to agree on how to divvy up the funding of $2.3 billion worth of work still needed to build the final runway and extension.
The new runway includes lighting and navigational technology that will allow more planes to land and take off in poor weather and with reduced visibility. During good weather, up to 150 planes an hour will be able to take off from the runway, according to the Federal Aviation Administration.
Chronic flight delays at O'Hare, where around half of travelers are just transiting, sent paralyzing shockwaves around the nation's air system in the late 1990s. It was a sign that you were an experienced traveler if you said you were trying to avoid O'Hare, Schwieterman said.
"You could hardly mention O'Hare without somebody pulling out a horror story," he said. "And that was well deserved. Everybody had seen trips go up in smoke due to intolerable delays."
Recent data indicates the airport still has some catching up to do.
Of the nation's 29 busiest airports, O'Hare ranked dead last in on-time departures throughout the first seven months of this year, with only about 67 percent of flights taking off on schedule, according to data from the U.S. Department of Transportation.
That represents a slip of three places in the rankings over the same period a year earlier, when O'Hare's on-time rate was 77 percent.
City aviation officials had to overcome numerous challenges to get to this midway point in the project. They fought a five-year legal battle with a church over a plot of land that included a cemetery started by German pioneers in the mid-1800s. The city needed the area for the expansion and relocated about 1,500 graves, agreeing last year to pay the church $1.3 million in a settlement.
American and United, which are helping bankroll the expansion project, sued Chicago in 2011 to stop it from issuing bonds to finance the project, arguing that the city was violating a lease the gives them authority to review and approve expenditures for capital projects. Then-U.S. Transportation Secretary Ray LaHood had to intervene to break that dispute.