The clock’s ticking on tunnel-mageddon.

Unless construction starts soon on new rail tunnels under the Hudson, Jersey commuters headed for Penn Station could lose (better sit down) 80 percent of service at some point in the years ahead.

Think commutes are hellish now? Just wait.

And it won’t be just New Jersey train riders who’d suffer — but the whole region.

The problem: The 105-year-old twin tunnels that handle train traffic under the river need vital repairs, especially after the damage caused by Hurricane Sandy. And no other tracks can pick up the load.

Each tube will have to close for a year, at least — leaving only the other to serve two-way traffic. Trains headed one way will have to wait for those going the other way to pass.

That’s just not enough trains to handle all 90,000-and-growing Amtrak and NJ Transit daily riders. Many will have to find other ways to commute: buses, cars, PATH trains, ferries — most of which are already at or near capacity.
That means more traffic. More delays. Rougher commutes.

Throughout the entire region.

Not to mention the huge economic toll: The time lost to longer commutes. The drop in suburban property values. The falloff in spending by, say, workers who no longer come into the city and buy lunch here. The dip in tax revenues.

Jersey’s Gov. Chris Christie killed a plan for new tunnels in 2010 — when no one could’ve known Sandy would ravage the existing ones just two years later. He was right to fret that his state would be liable for cost overruns from that megabuck project.

But planners have known for years that the aging tubes would eventually need repair — and that new tunnels were needed to handle soaring demand.

Over just the past 10 years, NJ Transit ridership to Penn Station has shot up more than 30 percent. And some say the number of train riders may double in coming decades.

Now Sandy’s made the problem dire.

The good news? Officials think they can finish new tunnels before the existing ones fail and disaster strikes — if they act quickly.

And key political leaders seem to understand the need for urgency. Federal Undersecretary of Transportation Peter Rogoff says building new trans-Hudson tunnels is the nation’s “most important rail project.”

But, he warns, Team Obama’s view may not be the next administration’s, in just 20 months. One more reason why “we don’t have any more time to waste.”

More good news: Preliminary work on the Hudson Tunnel Project is under way.
Bad news: Getting it done will cost $10 billion-plus, and no one knows where that’ll come from.

Let’s be blunt: Under no circumstances can this region be forced to live with massively reduced train service from Jersey. The project needs to go on the express track, pronto.

Local leaders need to do whatever it takes to head off disaster. Like speeding up environmental reviews. Stomping on Not In My Back Yard types. Waving off efforts to link the tunnel to far-less-urgent grand schemes, like a total re-do of Penn Station.

Most important (and difficult): They need to work out a funding plan to pay for it all — preferably one not as open-ended as the tunnel plan Christie nixed.

Jersey commuters need a sane way to get to work. New York needs its workers. Officials need to move fast — and avert a regional train wreck.