A much-needed plan to bring Metro-North commuter service through the eastern Bronx and into Penn Station is finally building momentum, thanks to a timely jump-start from Gov. Andrew Cuomo.

The idea has always seemed like a no-brainer.

Metro-North trains would use a stretch of the Amtrak northeast corridor, which runs from Penn Station under the East River to Queens, over the Hell Gate Bridge to Wards Island, and up the eastern side of the Bronx to New Rochelle and points north.

Metro-North would build stations at Hunt's Point, Morris Park, Parkchester and Co-op City in the Bronx.

Thousands of Bronx commuters would trade an hour-long express-bus ride for a 30-minute train ride. Thousands of riders from Westchester and other northern suburbs would love to have direct service to Manhattan's west side. And an army of housing and retail developers would like to see the eastern side of the burgeoning Bronx become less isolated from Manhattan.

Then there's the matter of preparedness. Cuomo rightly pushed that selling point last week as he touted the plan in his State of the State address. The project would make sure Metro-North stays connected to Manhattan should a Sandy-sized superstorm knock out the Harlem River lift bridge -- the railroad's only link today.

There is one catch. Penn is already the busiest station in America -- accommodating 1,200 trains and 650,000 riders each day. It is jammed impossibly tight. No new service can happen there before 2019 -- when the Long Island Rail Road starts running trains into Grand Central Terminal and freeing up platform space at Penn.

But don't worry. It's very hard to imagine that the MTA will build four Bronx stations and do other Metro-North upgrades before the end of 2019.

The MTA thinks the whole project could cost around $1 billion and intends to include it in next year's capital plan. This week's state Court of Appeals decision upholding the MTA payroll tax could help free up some money for it.

The MTA needs to keep this train rolling.