The most significant risk to the Alaskan Way Viaduct replacement project is the function of the tunnel boring machine itself, according to a new report by an expert review panel.

As of March 3, 2015, Bertha has traveled 1,083 of 9,270 feet. Crews are working to repair a broken cutter head after moving the machine into an access pit.

The report goes on to say that “this will remain as the single most significant project risk until the tunnel boring machine breaks through at the north end of the tunnel alignment.”

The good news is the panel predicts that despite Bertha’s breakdown, taxpayers might not be on the hook for extra money.

“It’s an underground project so it’s very common to have differing site conditions that occur in underground projects. The state had the foresight to understand that, know that and have the mechanisms within the contract to deal with those,” panel chair Dr. Patricia Galloway told KIRO Radio.

Galloway said a worst-case prediction shows Bertha’s breakdown will cost the state $317.5 million. The panel identified $329 million to cover those costs, including money from a contingency fund, an insurance policy on Bertha, and savings from other parts of the tunnel finished early.

The study also pointed out that little progress has been made to secure tolling revenues for the project.

“Delayed decision making on tolling matters creates the risk that future decision makers may have reduced willingness to authorize tolling,” the report said.

Without tolling, there isn’t enough funding to complete post-tunnel projects, the most costly of which is the new Alaskan Way surface street.

Despite the report, not everyone is convinced the tunnel will be completed.