It comes around every half-dozen or so years, but this time, when the gargantuan transportation bill is written, “smart growth” advocates are determined to play a prominent role — muscling aside the bill’s traditional highway heavy hitters.

How prominent a role, however, depends in part on whether the price of gasoline continues to hover around $4 a gallon, a price point that has suddenly made Americans acutely conscious of how much they drive.

“The onus is off us to make them pay attention,” said Geoff Anderson, president of D.C.-based Smart Growth America, which is co-managing the new coalition along with Oakland, Calif.-based Reconnecting America. “They’re paying attention.”

But the prominence of the smart-growth community in next year’s transportation bill, which could balloon to as much as $500 billion before it’s finished, also depends on the lobbying and grass-roots prowess of Transportation for America, a newly formed coalition that also goes by the snappier name T4.

The new group, which expects to have a $4 million budget, has already hired veteran strategist Donald Ross of M+R Strategic Services to map out a campaign plan that he said will include shoe-leather lobbyists as well as online, grass-roots and grass-tops advocacy.

T4 is consciously broad-based, because, they argue, it’s in everyone’s interest to promote the types of transportation policies that encourage people to live in denser communities that have a lower carbon footprint.

“The transportation bill has historically been fought within the confines of the Beltway and inside Congress,” Ross said. “But there has been the growth of organizations all over the country now concerned with transportation issues, directly or indirectly, there’s a much broader universe of people who will have concerns.

“People in the public health movement are worried about obesity because people aren’t walking,” Ross said. Real estate barons “who heretofore have not cared a tinker about transportation now do because they can do an infill building that can be very valuable,” Ross added, referring to the practice of building mixed-use structures in inner-city vacant lots.

The coalition began earlier this year with $700,000 in seed money from the Rockefeller Foundation — a “big deal,” Anderson said, “and a reflection of the growing importance that people are giving transportation.”

The idea, transportation consultant David Burwell explained, is that “transportation should support public policy outcomes. It’s not just about pouring concrete and pavement.”

The concept of smart growth has been around since the 1970s. Three transportation bills ago, during the landmark 1991 Intermodal Surface Transportation Efficiency Act, a transportation policy that emphasized transit and bike use as well as money for highways was actually enshrined in the legislative language.

But it was more a suggestion than a mandate. And despite two more multihundred-million dollar transportation bills since then, one in 1998 and the latest in 2005, there has been little progress on the issue. Local and state governments are still reimbursed for the cost of building highways at about 80 cents on the dollar; public transportation continues to be reimbursed at rates around half that amount.

Since the early 1990s, however, the world has changed, and $4-a-gallon gasoline is only an exclamation point on a far bigger trendline, Anderson said, and one that Congress has not yet fully recognized.

In 1996, for example, Anderson said, “zero percent of the residential market was being built inside D.C. Now, it’s around 15 percent.”

There’s an aging population, and a lower percentage of people having children, factors that can encourage couples to move back in to cities from suburbia. “It’s not fabulous to have to mow the lawn every week,” he said.

The war in Iraq has made clear to many people that there are ties between a U.S. troop presence abroad and an economy overdependent on oil. People are driving less, and, Anderson said, “transit is at a 50-year high.”

Global warming has moved from “people who say it’s happening versus people who don’t, to almost everybody who says it’s happening,” said Polly Trottenberg, a longtime Senate staffer who is now executive director of Building America’s Future, another coalition that supports infrastructure investment.

There’s also new, growth-sensitive political leadership on Capitol Hill, especially at the committee level.

In the Senate, Barbara Boxer (D-Calif.) chairs the Environment and Public Works Committee, which has a major piece of the transportation bill. In the House, the Transportation and Infrastructure chair is Minnesota’s James Oberstar (D); his crucial subcommittee chair on the transportation bill is Peter DeFazio, an 11-term Member from Oregon, a big smart-growth state, who heads the Highways and Transit subpanel.

Still, moving an entire Congress into the 21st century is a daunting legislative challenge. The 1998 Transportation Equity Act and the 2005 Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users, which weighed in at $286 billion, have inviolate old-line constituencies that reach back into the years when building the nation’s interstate highways was the federal government’s most important land transportation priority.

These include the American Association of State Highway and Transportation Officials as well as the American Road and Transportation Builders Association — interest groups that urban planner and author Jeff Speck said “have a stranglehold on Congress that’s as strong the [National Rifle Association] and probably more dangerous.”

Noted one Senate staffer: “The world up here is behind the world as we know it. The lobbyists who are powerful — AASHTO, ARBTA — represent the past; the lobbyists who aren’t powerful — the smart-growth types — represent the future.

“We have to get folks thinking in a broader way,” he said. “If you improve transportation to downtown Seattle and its port, that’s the best thing in the world for Montana beef growers and their refrigerated trucks.”