Today, Streetsblog’s Washington, DC branch has a thorough analysis of President Obama’s transportation bill, a leaked copy of which has been bouncing around transportation policy circles for the past few weeks. Encouragingly, the bill is full of alternative transit boilerplate, including $53 billion for passenger rail projects, $23 billion for various “livability”-related grants and initiatives, and a half-billion a year for cycle and pedestrian infrastructure grants. The bill would make an unprecedented amount of money available to local or state governments that are interested in building bike corridors, high-speed rail routs or bike share systems, and would replace the federal government’s troubled Highway Trust Fund with a less-discriminatory (and hopefully better-funded) Transportation Trust Fund.

But all of this comes with a huge catch. As Streetsblog’s Tanya Snyder explains, the president’s bill wasn’t exactly written with an eye towards with Congressional support:

The president’s bill, as we’ve mentioned, is useful as a standard to hold Congressional transportation legislation up against. It contains policies that would transform the highway-centric status quo, and reformers appreciate the administration’s decision to present an agenda that is such a quantum leap over previous funding levels, performance metrics, organizational structures, and priorities. However, don’t expect it to be central to the debate in Congress. By refusing to adjust to a still-struggling economy, high gas prices, and a deficit-obsessed Congress, the president has rendered his own plan moot.

And the plan is “moot” partly because of its dependence on a political third-rail: the federal gas tax:

“I don’t’ see how you get a bill passed without some deficit spending,” NRDC federal transportation analyst Deron Lovaas told Streetsblog, “and I don’t see how you deficit-spend in the current climate.” Certainly, he said, a gas tax falls further and further out of the realm of possibility as gas prices remain high, and that fact is tying this debate up in knots.

There’s a growing sense that gas prices could turn into a huge political liability for Obama, the sort of thing that would even jeopardize his reelection. And it’s easy to see why: even though we’re technically out of the recession, unemployment remains at around 9% while GDP growth was an anemic 1.8% last quarter, well below the 2% “natural growth” rate an industrialized nation could expect in an average year. High gas prices could help produce what’s basically a stagflated economy, driving up consumer costs in a time when people are still feeling pinched. While a higher federal gas tax would be an essential part of both encouraging and funding sustainable transit, increasing it could be politically suicidal at the moment.

But without some new source of revenue, an ambitious, national sustainability initiative like Obama’s might not get off the ground—especially considering the anti-spending atmosphere in Washington at the moment. Of course, that doesn’t mean that a less ambitious national sustainability initiative won’t be passed by Congress and signed into law this year. Stay tuned.