The rest is siphoned off by underutilized transit programs (20% of transportation spending, serving only 2% of travelers), national parks, Appalachia development, magnetic-levitation research, federal lands, covered-bridge repair, air quality, hiking paths, flower gardens and thousands of pork-barrel projects, one of which will spend $200 million on a bridge to an Alaskan island with 50 inhabitants. This year, Congress proposes new diversions for bicycle paths, battlefield preservation, adolescent obesity and storm-water runoff. Due in part to such leakages, road capacity has expanded only 7% since 1970, despite more than $700 billion in federal transportation spending.

As this worsening pattern suggests, Congress treats the highway program as a vast piggy bank from which to make periodic withdrawals on behalf of influential constituents. Thus, there is little reason to trust lawmakers to rise above these parochial pressures and refocus the program on highway congestion relief, new capacity and better highway maintenance.

With Congress a lost cause, the federal program should be capped at whatever level of spending the current gas tax delivers. Future growth in capacity and repair should come from greater reliance on tolls, with the resulting revenues dedicated to the roads on which they are earned, not to the politically influential. Such tolls should be entirely at the discretion of the states.

The highway program was created in 1956 to provide a valuable national service: construction of the interstate highway system. That goal was met by the early 1980s. It's time for Congress to declare victory and recognize that today's road problems are local and regional in nature, and thus no longer solvable by a Washington-based, one-size-fits-all, command-and-control system that has so badly failed us in recent years.

Ronald Utt is the Morgan senior research fellow at the Heritage Foundation.