You’ve likely been hearing a lot, on this blog and others, about the coming expiration of the federal transportation bill. Come September 30, Congress has to have a plan in hand to fund the nation’s trains, buses, bikes, bridges and roads — or pass an extension of the 2005 federal bill, locking in the same spending patterns that have nurtured Americans’ addiction to the automobile.

The federal transportation policy process: Thanks for clearing that up, guys! (Source: U.S. DOT).

But the odds are that you haven’t heard much about how the process works. What has to happen in order for Congress to meet that September deadline? Well, if you’re a fan of unnecessarily complicated Washington jargon, the federal DOT has a flow chart on the subject (pictured on the right):

Let’s break it down a bit. The hardest step in the transportation policy-writing process will be getting past the chart’s third box, out of the congressional committees.

Remember that immortal Schoolhouse Rock tune, "I’m Just A Bill"? The Bill famously sang that "it’s a long, long week when I’m sitting in committee," but it’s almost certain to take longer than a week to get the transportation bills onto the floors of the House and Senate.

There are two reasons for the delay. First, Republicans in Congress are salivating at the opportunity to rap Democrats for the local projects they prioritize in the bill — what you often hear called earmarks or "pork."

Now, what looks like "pork" to some looks like progress to others; House Transportation and Infrastructure Committee Chairman Jim Oberstar (D-MN) took heat from reporters in his own state for using earmarks to expand bike trails and commuter rail. But Republicans love starting earmark fights, no matter how counter-productive they are, and this year’s federal transportation bill will be no exception. (In fact, the process is already starting.)

The second reason that the transportation bill is almost sure to be delayed is money. Few people on Capitol Hill are ready to debate raising the gas tax or imposing a tax on vehicle miles traveled (VMT), although those are the only two concrete options on the table for bringing much-needed new money to the federal transportation trust fund.

But higher gas taxes and a VMT tax are good ideas, you may be thinking. Members of Congress, meanwhile, are thinking one thing: Why should we support new taxes on driving when President Obama doesn’t?

So getting out of the chart’s third box is going to be the hardest step. Still, that’s only the beginning.

You can skip the box marked "Any Differences?" because the chances of the House and Senate passing identical transportation bills are about as good as those of Transportation Secretary LaHood changing the name of his blog. The process of smoothing out differences between bills, called "conferencing," can take weeks or even months, depending on the circumstances. Then both chambers of Congress have to approve the unified transportation plan before it reaches Obama’s desk.

Even after the federal bill passes, however, state-level Departments of Transportation still have wide latitude to determine whether money gets spent on repaving a crumbling highway or adding a lane to one that’s hardly used. Lawmakers such as Rep. Jason Chaffetz (R-UT) have adopted a policy of steering cash directly to state DOTs.

As crazily complex as this process sounds — and it stalled spectacularly four years ago, when Congress was forced to pass twelve temporary extensions before they could agree on a transportation plan — there is an upside. The train-using, bike-riding public is watching closely this year, and any delay in passing the federal bill will provide more opportunities to get Congress on board with reforms such as "transit equity," which would require Washington to pay the same share for transit that it does for roads.

The first step, a transportation draft bill in the House, is expected just after the week-long Memorial Day recess.

And no matter how long the bill takes to pass, one thing is assured: It’s going to be an interesting summer for transit fans in Washington.