The next step in addressing a national transportation funding crisis came Monday night in a U.S. Senate proposal that would continue current spending levels for six years and give state and local governments more autonomy in how they spend federal dollars.

The long-awaited bipartisan bill, which was released without comment by Sens. Barbara Boxer (D-Calif.) and David Vitter (R-La.), would be pegged at around the current level of $52 billion a year, with an allowance for inflation.

“It’s not earth shattering, it’s pragmatic,” said Robert Puentes, a transportation and infrastructure expert at the Brookings Institution.

Taken as a sign of movement in an election year that has slowed Congress to a snail’s pace, the bill was reassuring to state and local transportation officials who feared their federal funds might be delayed or reduced by mid-summer.

The Senate bill brings to three the number of transportation spending plans under discussion. But based on Boxer’s track record of success, it became the front-runner against bills from the House and the Obama administration. Boxer was seen as the force behind the current plan that won approval in 2012.

After weeks of toil by the Senate Committee on Environment and Public Works, the Boxer bill landed in the middle of what advocacy groups have dubbed “infrastructure week,” a concerted effort to draw public and Capitol Hill attention to declining national systems said to need $3.6 trillion in restoration by 2020.

President Obama is scheduled to visit New York’s Tappan Zee Bridge on Wednesday, his latest foray to underscore the infrastructure issue. The 58-year-old bridge, crossed by about 140,000 vehicles each day, has outlived its natural life span and is set for a $3.9 billion replacement.

The Senate bill, which lays out a plan for spending but doesn’t specify where the money will come from, was being digested in advance of a committee hearing set for Thursday.

“While we begin the process of reviewing the specifics of the bill, we look forward to working with Senators Boxer and Vitter and the rest of the committee,” said Bud Wright, with the American Association of State Highway and Transportation Officials. “The nature of the projects and programs that state departments of transportation oversee require a long-term view in order to ensure the best investment of federal, state and local tax dollars.”

“Manufacturers can’t afford more delays,” said Jay Timmons, president of the National Association of Manufacturers. “Congress must bring the federal Highway Trust Fund to an improved condition of solvency.”

“Although we are still analyzing the bill, we hope the senate’s proposal will be another step forward in the race to reauthorize the critical funding needed to support the nation’s transportation system,” said Clarence E. Anthony, executive director of the National League of Cities.

The traditional source of funding for roads and transit projects, the Highway Trust Fund, relies on the 18.4-cent federal gas tax, which was last raised in 1993. The tax has not been adjusted for inflation, and the fund has eroded steadily as vehicles have become more energy efficient.

The Senate bill would provide federal support for state and local governments by continuing a popular loan guarantee program, allowing greater flexibility to streamline project delivery and create a new program to reward them for expediting projects completed under budget.

There are three key dates in the transportation funding crisis.

One will fall in early August, when the federal Highway Trust Fund is expected to run short of cash.

The second is Sept. 30, when the current highway spending bill expires.

The third is Nov. 4, when voters decide who will fill 33 seats in the U.S. Senate and all 435 seats in the U.S. House of Representatives.

If those dates were reversed, experts say the chance would improve that Congress might find the backbone to raise taxes in some form to fund transportation.

“I don’t think there’s any chance of it getting done this year,” Puentes said. “We’re going to figure out how to patch the trust fund from August to November. After the election, it’s anybody’s guess.”

The what-to-do and how-to-do-it questions invite complex and diverse answers. House Republicans this month rolled out a bill that cuts about $1.8 billion from current spending. The $302 billion Obama administration plan would permit $150 billion more in spending than the gas tax will bring into the trust fund.

No one facing reelection in less than six months wants to be blasted for raising the federal gas tax, but Puentes and other experts see no short-term alternative to revive trust fund revenues.

A quartet of influential advocates agreed Monday that a gas tax hike was the most feasible quick-fix option to avoid a scenario where states are forced to suspend summer-season construction projects for lack of federal dollars.

“Over a dozen states in recent weeks have publicly stated that the uncertainty with the Highway Trust Fund has caused them to delay, stall or reconsider major projects,” said Pete Ruane, president of the American Road and Transportation Builders Association, in endorsing a higher gas tax. “Over the next several weeks, we’ll be turning up the heat on Congress.”

Terry O’Sullivan, president of the Laborers’ International Union of North America, said his union would spend $1 million on billboards, radio and electronic media to raise voter awareness in three states — Pennsylvania, Michigan and Ohio.

“I would raise the gas tax,” O’Sullivan said. “If not that, can we cobble together an all-of-the-above strategy? We’re not opposed to any of the other alternatives that have been proposed.”

AAA lobbyist Jill Ingrassia also saw the gas tax as the best immediate option.

“Asking Americans to pay more isn’t easy, but on this issue in particular, it’s the right thing to do,” she said. “Voters understand roads aren’t free, and they are willing to support increased investment when they know that the revenue is going to be spent in ways that improve their travel experience.”

It has been estimated that the federal gas tax would have to be raised to 31 cents per gallon to revive the flagging trust fund. Most polls have shown that a majority of Americans oppose a gas tax increase.

A variety of other options have kicked around Congress for years, but few have gained much traction. The White House has proposed an expansion of transportation spending using money gained through corporate tax reform, a notion that rarely comes up unless an administration advocate is present. The administration spending plan included allowing states to impose tolls on interstate highways.

Another short-term solution that has won bipartisan support would allow U.S. companies that have stashed trillions of dollars offshore to bring that money home at a reduced tax rate, with that revenue going to meet transportation needs.

The mantra to date — used by the Obama administration, senators and conservative House Republicans — has been that all funding options must be considered.

“It is now up to the Senate Finance Committee to consider how Congress will fund this bill,” said AAA President Bob Darbelnet. “We are encouraged to see leaders in Washington addressing the transportation crisis with detailed proposals rather than general fund bailouts.”

Despite his organization’s support for a gas tax increase, Darbelnet said the finance committee should “keep all options on the table.”

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