It's crunch time for Congress: The latest extension on the country's transportation legislation is set to expire Saturday.

SAFETEA-LU, the law that authorizes federal spending on highways and transit, expired exactly 1,000 days ago today. Since then, Congress has passed a series of stopgap extensions to prevent its expiration.

As it stands, Congress is the closest it's ever been to passing a new long-term extension of the law, though that term is relative, since the long-term extension would actually last less than two years. The Senate has passed a new transportation bill, known as MAP-21. But the House failed to pass a long-term extension, and is now in conference committee negotiations with the Senate.

Those negotiations haven't gone smoothly. House Republicans have said Senate Democrats are relying on accounting gimmicks to fund the transportation program. Meanwhile Senate Democrats aren't happy that House Republicans are attaching controversial add-ons to the legislation, like approval of the Keystone XL Pipeline.

Last week, Sen. Barbara Boxer (D-Calif.), chair of the Environment and Public Works Committee, and Rep. John Mica (R-Fla.), chair of the Transportation and Infrastructure Committee, released a statement that was short on details but seemed like a sign of hope for the legislation after negotiations had stalled.

"The conferees have moved forward toward a bipartisan, bicameral agreement on a highway reauthorization bill," they wrote. "Both House and Senate conferees will continue to work with a goal of completing a package by next week."

Now, that deadline is essentially here. Senate Majority Leader Harry Reid (D-Nev.) has reportedly said an agreement must be reached by Wednesday for the legislation to be passed by the end of week, when the latest extension expires.

The sentiment among stakeholders is that it may already be too late for the conferees to agree to a long-term bill and get it approved by Congress in time.

If Congress doesn't pass an extension and allows the legislation to expire, it could lead to a halt among transportation work in states and localities across the country. Most transportation experts say that's not going to happen -- lawmakers learned their lesson when they allowed partisan brinkmanship to shut down the FAA last summer.

The more likely scenario is that this week, Congress agrees to yet another short-term extension. The big question is what will be the length of that short-term extension, and will Congress punt and defer work on transportation legislation to legislators in 2013 -- or continue to work in earnest on a long-term bill.

Underscoring all of this is the pending insolvency of the Highway Trust Fund, the dedicated stream that helps fund the federal government's spending on highways and transit. At some point in 2013, the portion that funds highways won't be able to meet its obligations. The same will happen to the transit account in 2014.

Transportation stakeholders have mixed feelings about the state of negotiations. State transportation officials are essentially at the point that they're ready to accept any legislation that Congress can produce so that they'll have certainty in their own jobs.

Since SAFETEA-LU expired, state transportation officials have bemoaned the fact that the endless slew of temporary extensions has made it difficult to project what their long-term funding picture will look like. That, in turn, has made them more cautious about pursuing big, long-term projects, since they are wary of making a financial commitment they're not sure they can keep.

"We can't let the perfect be the enemy of the good," said Kirk Steudle, head of the Michigan Department of Transportation and president of the American Association of State Highway Transportation Officials. "They're closer than they've ever been. If they punt, it's the worst thing ever."

The business community is also desperately urging reauthorization, with groups like the American Road, the Transportation Builders Association and the U.S. Chamber of Commerce pressing lawmakers to pass a bill as the deadline approaches.

For cities, which are fighting for the money and authority to fund biking and pedestrian projects, it's hard to say right now whether they'll ultimately support the final legislation, since it could wind up affecting programs city officials are fighting for. "We cannot have a transportation bill that turns its back on the needs of large cities," said Ron Thaniel, executive director of the National Association of City Transportation Officials.

Others from academia and advocacy groups are more skeptical. Josh Schank, head of the Eno Center for Transportation, a transportation policy think tank, said he fears that if Congress rushes to pass transportation, it might strip a key provision for which his group has advocated -- stronger performance metrics for evaluating transportation projects. "In that case," he says, "I'd rather have no bill."