TRENTON - One of Gov. Chris Christie’s top appointees has resigned amid an escalating probe into lane closures on the George Washington Bridge.

Port Authority of New York and New Jersey Deputy Executive Director Bill Baroni will step down immediately, Christie said at a news conference today.

Democrats have been holding hearings into the closures that took place in September. Baroni said they were closed for a traffic study.

Christie has denied having any knowledge of plans to close the lanes and says Baroni's resignation had been planned for a while. "He offered his resignation now, and I accepted it because I thought it was the appropriate thing to do given all the distraction that's going on," Christie says.

Democrats claimed they were closed to punish Fort Lee's Democratic mayor for not endorsing the Republican governor's re-election campaign.

Christie announced Deborah Gramiccioni would replace Baroni at the bistate agency. She worked with Christie at the U.S. Attorney's Office.