In his fourth and final term, Gov. Jerry Brown intends to start drilling two massive tunnels under the Sacramento-San Joaquin River Delta. Estimated cost: $25 billion.

Californians might consider the pitfalls of a smaller tunnel project in Seattle, subject of a recent article by the Washington Post. The dig will move two miles of State Route 99 underground and, according the state Department of Transportation, “clear the way for new public space along Seattle’s downtown waterfront.”

Washington Gov. Jay Inslee and Seattle Mayor Ed Murray support the tunnel, launched in 2009 at a cost of $2.8 billion. The project was slated for completion in 2015, but that is not going to happen.

“Bertha,” a 2,000-ton boring machine created specifically for the project, has advanced about 1,000 feet but quit a year ago with more than 8,000 feet to go. Trouble is, Bertha is unable to reverse itself. Engineers will have to excavate from above and remove the machine for repairs.

This could push the completion date into 2017. On the other hand, local officials estimate that 70 percent of the money has already been spent. Seattle politicians fear they will be stuck with the bill.

Even among supporters, the Route 99 tunnel had sparked comparisons to Boston’s Central Artery/Tunnel project. “The Big Dig” made news in 2006 when 12 tons of concrete fell from a tunnel ceiling and crushed to death restaurant worker Milena Delvalle, 38. But the problems did not start there.

The seven-mile Big Dig, a pet project of the late Sen. Edward Kennedy and House Speaker Tip O’Neill, spanned six presidential administrations and seven Massachusetts governors. The final cost was $14.8 billion, nearly 10 times what politicians initially claimed.

Shortly after the death of Delvalle, Boston University journalism professor Fred Bayles told reporters the Big Dig was “a dangerous and perhaps criminal boondoggle.” That caused no hesitation on the part of the Seattle diggers, and neither project appears to have given Gov. Brown any second thoughts on his tunnels, which make the others look like fence-post holes.

Each tunnel would be 40 feet high, 35 miles long, and, together, they would cost nearly $25 billion, part of the governor’s plan for the state’s water system. If subject to the same sort of cost overruns as Boston’s Big Dig, far from a remote possibility, they could saddle taxpayers with $250 billion.

Gov. Brown appears undisturbed by the financial, environmental and safety concerns of the tunnels. His brand of tunnel vision can’t reverse itself. It prefers to focus on the joys of spending and a glowing legacy down the road. The governor will be long out of office but California taxpayers, and their children, will be stuck with the costs.