The state Assembly and Senate voted Monday to establish a joint bipartisan committee with power to subpoena people and correspondence related to the traffic scandal and other matters. The two chambers had been conducting parallel investigations.
Chicago lawyer Reid Schar will serve as special counsel to the panel of eight Democrats and four Republicans.
Co-chairs of the committee say the focus is on finding out who ordered the blocking of two lanes of traffic near the George Washington Bridge, leading to hours-long delays in the town of Fort Lee, at the base of the span.
The U.S. Attorney's office has launched a separate investigation.
"This is the optimal approach to ensuring the people of New Jersey get the answers they need to these questions about the abuse of government power," said Assembly Speaker Vincent Prieto, whose transportation committee was further along in its probe than a parallel effort in the Senate.
The U.S. Attorney's office stepped up a criminal investigation of the matter with subpoenas to the Christie for Governor re-election campaign and the state GOP, and probably others last week.
Twenty subpoenas issued by the Assembly panel remain pending and are due back next week.
Those reach deep into the governor's office, the re-election effort and the Port Authority of New York and New Jersey, the agency that runs the bridge. None target Christie, a possible 2016 presidential candidate who has just begun a year-long chairmanship of the Republican Governors Association.
The governor has said he was not involved in the planning or execution of the scheme, which appears to have been authorized by his deputy chief of staff, Bridget Kelly, and carried out by his No. 2 man at the bridge agency, David Wildstein.
Kelly has been fired and Wildstein resigned.
Two other Christie confidantes also were let go: His top deputy at the Port Authority, Bill Baroni, resigned after telling a legislative panel the lane closings were for a traffic pattern study; and two-time campaign manager Bill Stepien was told to step aside after he appeared to gloat over the traffic chaos in private emails released in the investigation.
Christie, who has a reputation for engendering loyalty and insisting on discipline among his subordinates, explained in a December news conference that he learned of his aides' involvement when the subpoenaed emails were published.