At today's lengthy city council viaduct oversight committee meeting, a consultant hired by the city council to analyze the risks of replacing the Alaskan Way Viaduct with a deep-bore tunnel told council members that the tunnel had a 40 percent likelihood of costing more than the state's $1.96 billion budget. According to the state's Cost Estimate Valuation Process (CEVP), the tunnel is 60 percent likely to cost $1.96 billion or less, and 40 percent likely to cost that much or more. The state estimates that the tunnel has a 90 percent probability of costing less than $2.2 billion.

Put another way, there's a 30 percent chance that the tunnel will have overruns of up to $300 million. A 2004 study found that, on average, tunnel and bridge megaprojects go 34 percent over budget.

"When things go wrong with tunnels, and they can go seriously wrong, it can lead to cost overruns," the consultant, John Newby, said. State viaduct project staffers did not refute Newby's numbers, but they did rush to qualify that the cost estimates will be more reliable once the two remaining contractors actually submit their bids on the project.

The meeting was mostly a rundown of all the potential pitfalls that could lead to cost overruns, including: Unanticipated soil conditions, wear and tear to the tunnel boring machine (which will be the largest of its kind, by three feet, in the world), and ground deformation or settlement during tunneling.

After the meeting, council member Mike O'Brien, a tunnel opponent, told PubliCola he wasn't comforted by today's presentation.

"At some point, risk is risk, and either the contractor has got to bear it or the public has got to bear it," O'Brien said. O'Brien wants the council to ask the state legislature to remove a provision in state law that says Seattle taxpayers will be on the hook for any cost overruns on the tunnel.