The tunnel, nicknamed the Access the Region's Core (ARC) project, was expected to double commuter-train capacity between New Jersey and Manhattan. In September 2010, Christie shut down construction, which had started a year before, to conduct a 30-day review of the project. Less than a month later, he announced that the state would no longer participate in the project, claiming New Jersey could spend as much as $5 billion on cost overruns. He cited state transportation officials, who had revised their cost estimate for the project to between $11 billion and $14 billion from $8.7 billion.

But the GAO report disputes Christie's numbers, claiming the project's cost estimates hadn't changed in the two years before construction was shut down. When announcing plans to shutter the ARC project, Christie said New Jersey was responsible for 70% of the bill, but the report indicates the state was on the hook for only 14.4%. No final agreement had been reached with the federal government to determine who would pay for cost overruns, the report contends.

New Jersey Senator Frank Lautenberg (D), who requested the GAO study, said Christie killed "the most important transportation project of our time" in order to curry favor with the national GOP and solidify his reputation as a cost-cutting fiscal conservative.

Christie's office has rejected the GAO's report as well as a barrage of criticism from New Jersey Democrats, saying the governor stands behind his decision.

"The ARC project was a very, very bad deal for New Jersey," Christie spokesman Michael Drewniak said in a statement. "The ARC project is still dead, and it's not coming back."