Governor Chris Christie on Friday said the chairman of the Port Authority of New York and New Jersey had resigned, a day after an internal investigation cleared Christie in the "Bridgegate" scandal embroiling the potential 2016 Republican presidential contender.

David Samson, a lawyer and ally of the governor at the agency that oversees bridges and tunnels connecting the two states, had been discussing for a year his desire to step down, Christie told a news conference.

"David tendered his resignation to me this afternoon, effective immediately," Christie told reporters, his first news conference since a two-hour-long question and answer session on January 9 after a scandal erupted over the closure of traffic lanes on the George Washington Bridge.

Christie spoke to reporters a day after a law firm hired by his office released a report finding him faultless in the massive traffic jam last September, which was apparently orchestrated by his senior staff possibly as political payback.

Critics of Christie quickly dismissed the report as a whitewash.

Christie defended the report, which blamed former deputy chief of staff Bridget Anne Kelly and Port Authority official David Wildstein for closing bridge entrance lanes in an apparent bid to retaliate against the Democratic mayor of the town of Fort Lee who had not endorsed Christie's 2013 re-election campaign.

On Friday, Christie repeated the assertion he has made since the scandal first broke that he was unaware of his aides' apparent political motives in ordering the lane closures.

"Nobody dropped the ball here," Christie said. "If I knew then what I know today, we would have done a lot of things differently."