Congress is running out of time to pass a transportation bill. If lawmakers cannot forge an agreement, they will need to fund projects on the nation's roads and bridges with a stopgap measure.

Again.

Congress last passed a surface transportation bill in 2005, and since that bill expired in 2009 lawmakers have enacted nine straight short-term extensions. They now have until June 30th to avert a scenario in which construction projects come to a halt as money for them dries up -- something neither party wants to happen.

Senate Majority Leader Harry Reid, Democrat of Nevada, upped the pressure on Tuesday, saying a deal needed to happen on Wednesday in order to leave enough time to get the bill to President Obama before the current pot of funding evaporates.

We have to have an agreement by tomorrow, Reid said on Tuesday. Otherwise, we can't get the bill done. 

Congress' failure to pass a long-term surface transportation bill at a time when the nation's deteriorating infrastructure earned a D grade from the American Society of Civil Engineers has emerged as a symbol of dysfunction on Capitol Hill. President Obama has repeatedly stressed investments in infrastructure as a means to stimulate the economy and produce jobs, but to no avail.

Disagreements about how to pay for the bill have been part of the problem. Last time around, House Republicans rejected a Senate bill in part because they said that federal gasoline tax revenue, the traditional source of funding for surface transportation projects, was insufficient. They pushed to have new offshore drilling included, saying the royalties from new projects would help cover the shortfall.

The Keystone XL pipeline also continues to be a sticking point -- Obama has put the project on hold pending an environmental review, but Republicans want transportation legislation to include a mechanism that would accelerate the natural gas pipeline. They also want to ease restrictions on coal-ash pollution.

Another possibility is that the transportation bill gets rolled into separate legislation that would prevent interest rates on student loans from doubling. Senate leaders said on Tuesday that they had completed work on the student loan bill and kept alive the possibility that transportation language could be included.