Crews started working Monday night on replacing hundreds of the steel beams that support the 82-year-old span.
For now, three lanes into New Jersey will be shut during most overnights. The work is expected to last at least through the end of the year.
The repairs are being funded by phased-in toll increases implemented in 2011 that will ultimately raise cash tolls from $8 to $15.
The Port Authority says more than 49 million vehicles crossed the span last year from New Jersey into New York City.
Delays of 45 to 60 minutes were worst on the first night, but expected that to be the norm could be an optimistic assessment. A test run two weeks ago produced 90-minute-delays, albeit with no public notification, said Port Authority tunnels, bridges and terminals director Cedrick Fulton.
"There are going to be delays, no question about it," Fulton said. "We're trying to communicate with the public and urge them to change their driving habits. We're trying to push as many cars as possible down (to the lower level)."
The $82 million repair will replace the steel beams underlying the upper deck roadway, which were last replaced in the late 1970s. They were designed to have a 20-year life span, but tests every two years showed they had maintained their integrity, Fulton said. But in recent years, according to bridge chief structural engineer Bernard Yostpille, small cracks had begun to crop up with greater frequency, leading to increasing repairs. The bridge was never in danger from the cracks, said Andrea Giorgi Bocker, engineer of construction for the bridge.
Fulton said one concern is that some motorists won't take the warnings seriously because a project last year to shore up a structure on the New York side of the bridge led to far shorter delays than were expected.
Two years ago, a weekend-long closure of a portion of Interstate 405 in Los Angeles was dubbed "Carmageddon" but didn't produce anything resembling the epic traffic jams that many feared. Another weekend closure last fall didn't produce "Carmageddon II," as many motorists stayed off the road.
Work schedules also will be tailored around the New York Yankees' home games in the Bronx, Port Authority officials said.
(The Associated Press contributed to this report)