If you think our roads and bridges are in terrible shape, along with mass transit, you’re right. And it’s altogether possible you ain’t seen nuthin’ yet.

A critical renewal of federal support for transportation is going nowhere fast, with the clock ticking down toward a June 30 expiration date while House and Senate leaders fight over who’s to blame for the partisan gridlock.

For decades, federal legislation has supported the nation’s transportation infrastructure, although at a level that increasingly falls short of the need. The organization representing the nation’s civil engineers says the U.S. road system rates a D-minus as conditions deteriorate “to the point at which Americans spend 4.2 billion hours a year stuck in traffic at a cost of $78.2 billion a year in wasted time and fuel costs — $710 per motorist.” The poor condition of roads adds another $67 billion in repairs and operating costs to the bill.

Annual surveys consistently rate congestion on Miami’s roads and streets among the 10 worst in the country. As for mass transit, Congress’ dysfunction jeopardizes about $184 million in funding for Miami-Dade County, the current allocation for trains and buses.

In the past, Congress dealt with the issue by approving transportation bills covering five or six years, which allowed for orderly planning. Since 2009, when the last multi-year extension expired, it’s limped along on at least nine short-term fixes, making the dispute over transportation funding a case study in congressional dysfunction.

The inability to win agreement requires repeated confrontations in Congress over extensions, makes planning impossible and raises the prospect that one day there will indeed be a cutoff.

This time, the Senate is taking the high road. One of its most liberal members, Sen. Barbara Boxer, D-Calif., and one of its most conservative, Sen. James Inhofe, R-Okla., are jointly spearheading an effort to get House members to agree to a bipartisan version passed in the Senate 74-22 that extends funding for two years.

No one calls it a perfect bill. It provides for only a two-year extension, rather than a longer version, hoping that by the time that expires, the bitter division in the House will have dissipated somewhat. (Good luck with that.) But at least it avoids costly and wasteful confrontations, which is why Sen. Inhofe is pressing his House colleagues to go along. “There is a conservative position in this. And that is to have a bill.”

House GOP members have made unacceptable demands. They want to slash funding for Amtrak, stiff-arm environmental-impact analysis of projects, and require approval of the Keystone XL pipeline. The most alarming provision eliminates dedicated funding for mass transit.

For decades, this has come from the federal tax on fuel. By making mass transit dependent instead on uncertain annual appropriations, every metropolitan area in the country could see traffic grind to a halt.

Instead of using the transportation bill as a vehicle for ideological issues, House GOP members should line up with their Senate colleagues. There is a clear need to provide federal funding for all forms of transportation.

In addition, the bill would also provide hundreds of thousands of jobs, particularly in the ailing construction industry, which suffers from 14 percent unemployment. A funding cutoff at this time would be a new low in congressional irresponsibility.