Opinion

Pipe dream No. 7

MTA Chairman Joe Lhota has thrown cold water on Mayor Bloomberg’s nutsy notion of extending the No. 7 line to Secaucus — and good for Lhota.

In a speech to construction industry executives on Tuesday, Lhota said: “I told the mayor this, I told the deputy mayor this: I can’t see this happening in our lifetime.”

Then, even more emphatically, he said there was “not a chance” that it happens.

To be clear, there would be nothing intrinsically wrong with another mass-transit tunnel to the Garden State.

The more the merrier.

Back on Planet Earth, however, pipe dreams must be paid for.

And the cash just ain’t there.

Lhota’s absolutely right — for a variety of reasons.

An extension beyond the 7 train’s (currently under construction) endpoint at 34th Street and 11th Avenue would cost an estimated $5.3 billion.

That’s real money.

But anybody who believes that sum to be anything other than a starting point knows nothing about how construction financing works in New York.

Should the low-ball figure somehow hold, there’s no money to meet it. Even Bloomberg’s boosterish $250,000 preliminary project study is not expected to identify a funding source.

There are practical considerations, too.

Even in the best of circumstances, extensive transportation upgrades take years, if not decades, to complete.

A Second Avenue subway was first envisioned in 1920 — followed by the better part of a century of abortive starts.

Now the first phase of a dramatically scaled-back line is scheduled for completion in 2016 — with no guarantee that the target date will be met.

And that’s only a New York City line.

Imagine the complexity of a project involving two states, which necessarily means two governors and — necessarily — the elephantine Port Authority.

As we noted when the mayor first mooted the idea in earnest last fall, he clearly hadn’t bothered to see if Gov. Cuomo was on board.

Lhota’s unequivocal kibosh answers that question: As a gubernatorial appointee, the MTA director quite obviously is speaking for the boss.

As well he should.