The governor of Pennsylvania might celebrate this evening by adding a little manchego cheese to his Philly cheesesteak.

The reason? Citigroup and the Barcelona-based infrastructure firm Abertis won the auction for a 75-year lease on the Pennsylvania turnpike with their $12.8 billion bid. The Pennsylvania legislature, much of which has expressed skepticism about the privatization of the state's 537-mile turnpike, still has to approve the deal struck by Governor Ed Rendell.

While $12.8 billion sounds like a lot—indeed, it would be the biggest privatization of a U.S. infrastructure asset to date—it's far from certain that the state would emerge a winner in this deal.

Infrastructure assets have become the investment du jour for many Wall Street banks and private equity firms in recent years. And as the credit markets collapsed, interest in public projects has only swelled in the past few months.

Just last week, Morgan Stanley announced it had raised $4 billion for a new infrastructure investment fund, exceeding its $2.5 billion target. Also last week, the private equity firm Kohlberg Kravis Roberts & Co. announced it has formed a global infrastructure practice.

It's easy to see why there is interest. Infrastructure, which includes public projects like turnpikes, water treatment facilities and airports, holds the promise of stable revenue streams, consistent returns, and almost no concern about competitive forces. Investors are promised worry-free, stable returns. Portfolio.com's own Felix Salmon is a fan of infrastructure privatization.

In private hands, the theory goes, tolls can be raised without political backlash, and the private turnpike operators can maintain roads with more efficiency and fewer obstacles.

But if the returns are so great, why are states scrambling to unload these assets? One reason is that they want to capitalize on the interest while it's here—the more money that's raised for these investments, the more bids submitted at auction, and the higher the prices.

But the Pennsylvania turnpike auction doesn't show signs of unreasonable froth. While the first bid came in much lower, at $8.1 billion, the final offer of $12.8 billion is still on the low end of what Morgan Stanley valued it at when it was hired as an adviser to the state of Pennsylvania. Morgan Stanley estimated the turnpike's worth at $12 billion to $18 billion. And just a year ago, sources told BusinessWeek the turnpike could fetch as much as $30 billion.

Indeed, the Philadelphia Inquirer reports that some members of the legislature are disappointed with the offer. "To be quite candid, the number is less than overwhelming," said Representative Keith McCall, head of the Democratic majority. "It's certainly not dead on arrival, but it's something we do need to discuss with the entire caucus."  

States should weigh these deals very carefully. While the windfall would certainly satisfy immediate cash needs for municipalities facing shortfalls during this period of economic upheaval, they might also be sacrificing long-term gains for short-term fiscal solutions.

They might be wise to follow the money instead. After all, if the so-called "smart money" is fighting over infrastructure for its promise of stable returns, chances are that similar returns could also be realized if they stayed in the public domain. Provided, of course, it has the financial competency to run them.