Gov. Chris Christie’s transportation commissioner will resign this month as federal investigators continue a wide-ranging probe into the Port Authority of New York and New Jersey, which he previously lobbied on behalf of United Airlines.

Jamie Fox’s departure a little more than a year after his appointment also comes as New Jersey lawmakers struggle to find a clear path forward on funding road work next fiscal year.

“I returned to government understanding it would entail a personal sacrifice and that it would not be a lengthy stay,” Fox said in a statement Friday. “I had hoped that we could secure a credible long-term solution for the Transportation Trust Fund within a year. I deeply regret we were unable to do so, and with a year behind me, it is time for me to return to the private sector and pursue new opportunities.”

The connections among United, transportation officials and the Port Authority are part of a federal investigation that began when Christie appointees allegedly created a traffic jam on approach lanes to the George Washington Bridge. The investigation has expanded to include the Port Authority’s actions at Newark’s airport, including some involving United that led to the ouster of CEO Jeff Smisek.

Port Authority records show that Fox dined with Smisek, the Port Authority’s then-chairman, David Samson, and other top Port Authority and United officials during the months when the airline was lobbying for items at the Newark airport.

Earlier Friday, Christie brushed off questions about Fox as he was discussing preparations for storms that were battering the state’s coastline.

“There’s absolutely no reason for us to be addressing that when we have to address this,” Christie said. “I appreciate all of your concerns for Commissioner Fox, but he is at work, and working hard, along with deputy commissioner (Joseph) Bertoni, to make sure that our transportation systems, both rail and automobile, around the state are in good working condition so that folks can make their way around the state despite whatever weather challenges we have.”

Christie said in a statement that deputy commissioner Joseph Bertoni will take over as acting commissioner but that Fox will remain on the job as the state weathers a severe rainstorm this weekend.

Fox previously worked as a top aide to former Gov. Jim McGreevey, including a stint as his transportation chief in 2002, and to U.S. Sen. Robert Torricelli.

Fox said being transportation commissioner under governors from two parties “has been the best job I have ever had.”

His second tenure as transportation commissioner has been dominated by debate over the state’s transportation trust fund, which faces insolvency with no agreement over raising the gasoline tax.

Fox warned legislators that by June 30 the transportation trust fund will run out of money to meet its debt obligations, and no new bonding has been authorized to pay for road and bridge work.

Christie has said he’ll consider raising the gas tax but only if it’s paired with other tax decreases, which he called “tax fairness” for residents.

The Democrat-controlled Legislature has not acted on any legislation to head off the funding problem.

Assembly Speaker Vincent Prieto praised Fox in an interview with The Associated Press, saying there was no better advocate for the state’s infrastructure than him.

“He’s been a great commissioner. He’s been a friend,” Prieto said. “He was a very good ally in trying to get our transportation trust fund done and his leadership has been extraordinary.”

Fox, a longtime Democratic insider, was involved in a tangled web surrounding an aborted United effort to fly to Atlantic City’s airport. The board that manages the airport decided not to require United to repay $104,000 in marketing incentives after the airline canceled the flights in December after eight months.

Fox spokesman Stephen Schapiro said earlier this week Fox had never voted on any matters affecting United since Christie appointed him commissioner in September 2014.

Schapiro also said the fee reimbursement issue regarding Atlantic City airport was a “staff decision,” which, he acknowledged, Fox agreed with. He added that since the matter had never been subject to a board vote, Fox never recused himself, which would usually be required under conflict-of-interest rules because of his prior work for United.

Photo Credit: New Jersey State Transportation Commissioner Jamie Fox answers a question about the closure of the right lane of the Route 3 bridge eastbound, seen behind, over the Hackensack River, which leads to the Lincoln Tunnel. Mel Evans / Associated Press