Of all the ways the Metropolitan Transportation Authority could spend its windfall, a giant platform on the West Side has got to be one of the worst. Yet that is exactly what the agency wants to do with $481 million of its unexpected $833 million surplus.

The most recent bout of platform fever arose from an attempt to build a new stadium for the Jets (and the Olympics) atop the rail yard just west of Penn Station. That deal, which would have consumed at least $300 million of taxpayers’ money, crumbled when it went before the Public Authorities Control Board. The Jets still purport to be interested in the site, but, despite a deadline extension, they have yet to make a down payment on usage fees for the site.

Undeterred, the MTA appears willing to take a “build it and they will come” approach, erecting the platform and worrying later about who will build on it. Katherine Lapp, the executive director of the authority, likens the platform to Rockefeller Center and Lincoln Center, saying that the MTA plan would have a similarly transformative impact on the neighborhood.

The platform may indeed be “bold” and “creative” – Ms. Lapp’s words, as reported yesterday by our Jeremy Smerd – but it is also none of the MTA’s business. Last we checked, the “T” still stands for “transportation.” Since the platform will not move anyone anywhere, the authority would be more on mission were it to find better ways to spend the riders’ money.

There are many worthy candidates. The MTA is holding out its cap for half of the $2.9 billion statewide transportation bond issue recently placed on November’s ballot. If the agency insists on asking taxpayers to go into debt to fund the Second Avenue line or the no. 7 – and Long Island Rail Road extensions – it could soften the blow by applying almost half a billion dollars of hard cash to these projects. Or the MTA could give its long-suffering riders a fare cut. Or even just make it possible for the subway to run in the rain. Best of all, there’s the MTA’s own “Plan B” for the surplus, beefing up the agency’s underfunded pension system. This would mark a welcome burst of fiscal prudence and would translate into ongoing savings of $38 million a year.

Building a platform on the West Side is not a bad idea, but it’s the wrong idea for the MTA. The location could be the home for any number of projects that would revitalize the neighborhood and help boost the city’s economy. But the MTA isn’t the right agency to spearhead such development, especially when projects related to its core mission are crying out for investment.