At issue now is not building replacements, but how fast it can be done. The customary pace of public works projects puts the entire region in peril.

If just one of the two tunnels has to be shut down, which could happen at any time, it means train traffic will have to be reduced not by half, but by 75 percent, from 24 trains per hour to six. That’s because the sole remaining tunnel will have to be used for two-way traffic, and time will be lost in reversing signals, according to “Billions for Red Tape: Focusing on the Approval Process for the Gateway Tunnel Project,” a report from the Common Good, a group that advocates the reform of government processes.

The group is calling for President Obama to issue an executive order that would turn over authority for environmental review on the project to the chairman of the Council on Environmental Quality, and for other permitting issues to the federal Office of Management and Budget.

The point is to limit years of meetings with 20 agencies sitting around and planning yet more meetings, said Philip K. Howard, the president of Common Good.

“Inaction is the worst result of all,” Mr. Howard said.

The very words “environmental review” cloak a process in virtue and goodness, but if prolonging it means that the region loses one of those rail tunnels, it would be more destructive than many environmental calamities. The loss of even one tunnel would force more people into cars and lead to hundreds of thousands of tons of emissions.

An earlier plan for new rail tunnels underwent about six years of environmental review. The tunnels were canceled by Gov. Chris Christie of New Jersey in 2010, who said the costs had swollen. (Mr. Christie, a Republican, redirected funds to keep gas taxes low and to prop up the state budget.) Some of the earlier studies can be used to advance the current project, officials say.

Federal officials have now promised to finish their review in two years. Mr. Howard’s report estimates that permits will take an additional year after that. If those three years could be cut in half, he said, the project would save $3 billion. Patrick J. Foye, the executive director of the Port Authority of New York and New Jersey, estimates that every month of delay adds $80 million in costs. For that reason, he said, it is important that officials at the Port Authority — and other agencies — not become prisoners of process.

Environmental review is an essential, if wonky, maze that cannot compete with the smoking-gun clarity, and villainy, of the “Time for some traffic problems in Fort Lee” note that announced the scheme to tie up traffic at the George Washington Bridge. But it will be far more destructive if it means we have one fewer tunnel — or two — under the Hudson.