Jacquelyn Martin/AP Photo

The countdown clock has officially been broken out. There are just three days left until construction on roads across the nation could come grinding to a halt unless Congress passes a transportation bill.

This Saturday is the deadline to pass a highway bill before federal funding expires but, as of now, the Senate and the House are deadlocked with no agreement on a way forward on one bill.

Two weeks ago, the Senate passed a two-year $109 billion transportation bill with a large bipartisan vote that won the support of 22 GOP senators.  Since then, however, the House of Representatives has grappled with its own way forward.

House Republicans could not originally find support for a five-year, $260 billion measure. So instead of passing the Senate's two-year bill, GOP leaders have been trying to pass a short-term extension instead.  That bill has been "on the calendar" every day this week in the House, but twice already GOP leaders have postponed votes on short-term extensions.

Today, Senate Democrats increased the pressure on the House to pass the Senate's two-year bill rather than a short term extension. Democrats unveiled a "countdown clock" at a press conference today to intensify the urgency of the situation. The clock shows three days left, until a "transportation shutdown" - when highway projects nationwide would stop if no bill is passed.

With work on the roads at a standstill, construction workers working on federal highway projects would be laid off, as the U.S. government would no longer be able to collect a gas tax, amounting to $93 million a day.

"Once again, we're facing the specter of an unnecessary shutdown because of the intransigence of the House GOP caucus," Sen. Chuck Schumer, D-N.Y., said today. "Should we reach March 31 without passing a bill, states' contract authority for construction projects would cease."

If there were to be a lapse in funding, Democrats said, 2.9 million jobs would be threatened.

"Time is running out," Schumer said. "If Speaker Boehner put the Senate bill on the floor, there's virtually no question it would pass by a large majority."

Democrats today would not specifically rule out passing a short-term extension to avoid a shutdown, perhaps a 60-day extension with a motion to go to conference committee to negotiate a longer-term bill. But they would rather focus on trying to force the House Republicans' hand to accept their bill.

"The one solution is to pass the Senate bill," said Sen. Barbara Boxer, D-Calif.

"The bottom line is there is an easy way to resolve it, which is for the House to pass the Senate bill," Schumer added.

The House is scheduled to start a two-week recess on Friday, with the Senate scheduled to start its recess on Monday. Current highway funding runs out Saturday, March 31.