Woe betides Long Island commuters this week.

Sunday, a passenger-less Amtrak train derailed under the East River. Because Amtrak and LIRR share quarters in this tight space, the severe damage to Amtrak’s rails that ensued has hit the MTA’s Long Island Rail Road. LIRR has slashed service by up to 25 percent at least through the middle of this week.

The incident is another reminder that New York needs better rail capacity to and from Manhattan.

The good news is that Amtrak is getting $295 million from the feds to attack this particular bottleneck, which regularly affects commuters’ quality of life.

The bad news is that in just seven months, the MTA will have no money to sign its own new capital-investment contracts for the LIRR as well as the rest of downstate New York.

Replacing and maintaining rails and the like is expensive, never-ending work — so with a smaller no capital budget, commuters across the downstate region should expect more weeks like this one.

Gov. Cuomo should commit funding a new capital budget — but only if:

• the private construction workforce that does most of this type of work for the MTA commits to better work rules, achieving double-digit percentage savings over the next half-decade, and
• the state can do something to cut LIRR labor costs. Pension costs alone are rising 37.3 percent over four years, to $220.3 million. Legislative pension fixes across the state workforce would help the LIRR, too, but unfortunately, for bigger savings, we really do need President Obama’s help.