Most travelers going through Kennedy International Airport did not really notice that the biggest runway there had been closed for four months of repairs.
For the stressed-out officials overseeing the $376 million project, that may have been the biggest accomplishment of all.
Runway 13R-31L, which reopened Monday, is a picturesque strip that handles a third of the airport’s air traffic. Before the runway shut down in March, pessimists, and even a few newspapers, predicted a chaos of delays and tarmac traffic jams at one of the nation’s busiest hubs.
But airport officials are happy to report that the number of delays during the construction period stayed more or less the same as last year, when about one in every five flights left late.
And save for one scary day in March, when high winds forced the airfield to operate on a single runway, the repairs went off with few problems and little fuss.
“The public cynicism for the capacity of an agency like the Port Authority to build on time, or on budget, is pretty high,” said Christopher O. Ward, the executive director of the authority, which operates the airport. “Failure would have been unacceptable.”
The repairs are expected to reduce delays at the airport and save millions of dollars in long-term maintenance. The lifespan of the runway, the second longest in the country, is expected to be extended by 40 years.
Its newly widened span can now accommodate the most advanced aircraft in the world (including the space shuttle). And its murky asphalt surface has been replaced by bright white concrete, producing a beaming strip along Jamaica Bay.
Just before noon on Monday, a JetBlue airplane taxied to the repaired runway and took off for Tampa, Fla. It was the first aircraft in four months to take flight from the landing strip, which was finished days ahead of schedule.
To choose which airline would be the first to try out the restored airstrip, airport officials picked a name out of a hat. But that may have been the only unplanned component of an ambitious renovation that was nearly four years in the planning stages before a shovel ever hit the ground.
The goal, at the start, was simple: to restore a heavily used runway that was overdue for a spruce-up. Long known as the Bay Runway, the airstrip was in operation when Kennedy, then called New York International Airport, opened for commercial flights in 1948. But its last overhaul was in 1993.
The airport built two and a half miles of barbed-wire fencing to isolate the construction area, to conform with federal security regulations. It paved a new access road to give machinery a direct path onto the airfield. And a cement plant, capable of producing 4,000 cubic yards of it daily, was built on the premise of saving travel costs and time.
The project was timed to coincide with springtime’s drier air and lighter travel load, but officials had to deal with a major variable: the fickle weather of New York City in March, April and May.
“Every week we hit the milestones was a week of relief,” Mr. Ward said.
A nail-biter took place on March 13, when winds swept through the airfield at upward of 65 miles per hour. About noon, the airport was forced to close all but one of its four runways, and those runways stayed closed for most of the day. Mr. Ward described his team as “pretty darn anxious.”
About 24 percent of departing flights at the airport were delayed in March, up from 16 percent a year earlier, according to data from the federal Bureau of Transportation Statistics. But in April, only 16 percent of flights were delayed, down from 21 percent a year ago.
Concrete is a more durable substance than asphalt, which saves repair costs in the long run. But it takes much longer to install and is not commonly used for runway rehabilitations.
The airport used a machine that paved 1,000 feet a day, but contractors still found themselves working more weekends than expected.
Airport officials had hoped to install a new design feature on the taxiways that would allow planes to overtake one another in the queue, a method for speeding departures. But the plan was not approved by the Federal Aviation Administration, which worried that pilots might be confused by lack of signs, a F.A.A. spokeswoman said.
About two-thirds of the 14,572-foot-long runway is now back in operation. A final, smaller segment will be repaired in September, which will require the closing of an intersecting runway for two weeks.
But Mr. Ward said the project was over its biggest hump. “And we don’t have to think about it for another 40 years,” he added.