"One concern is that Congress might think TIFIA is too big because not all of the funds have been obligated, says Geoffrey Yarema, a partner with Nossaman, a law firm specializing in infrastructure. "It's important that Congress understand the demand for the program outstrips the program size, even with the huge increase."

That possibility, Yarema adds, "would be horrible." Future demand justifies a further increase in the next reauthorization, he adds.

But even more crucial are Private Activity Bonds (PABs), which became available for highway and transit projects under a demonstration program in 2005.

"The ramp-up of the use didn't take place as quickly as we'd thought , largely because of the capital markets crisis," says Yarema. "We predict that by 2015, the $15 billion cap will be hit. What happens then? If you look at the success story of P3s since 2005, one of the biggest commonalities is the utilization of PABs. Without them, we're very concerned. It would be a huge reversal of a trend that is gaining significant approval."

P3s and alternatives to design-bid-build also are gaining significant appeal "as agencies are starting to understand them better," says Mike Hoover, executive vice president and chief operating officer with Sundt Construction Inc., but adds that many contractors are still not familiar with them.

Nor are some engineers and designers, adds Robert Brustlin, president and CEO with VHB Inc., noting that relationships with contractors require a different mind-set under design-build projects. "It's a 24-7 commitment," he says. But it encourages creative, accelerated solutions to infrastructure problems, he adds.

"In general, the importance of teaming has never been as profound as it is now," says Paul Boggs, business development manager with Trumbull Corp. "Bidding the job is the easy part now. Finding the right team members, the right combination of talents, finding the people with the best presentation to the owner—that is such a key element of what we do now. It makes pricing the job almost secondary. We're all coming to terms with that."

A P3 stretches the relationship flowchart even farther, notes Charles O'Reilly, transportation director for HDR Inc. "New players may include financial institutions, developers, operators and maintenance providers," he says. "Adding these players complicates many areas, including liability insurance and a desire to progress the job before financial close."

There is still a learning curve, but states are increasingly willing to navigate it, says Sidney Florey, head of North American business development for the French firm Vinci, one of many global concessionaires pursuing the ripening P3 market in the U.S. "We've seen increased interest" thanks to successes in pioneering states such as Florida, Virginia and Texas, he says.

Karl Reichelt, executive vice president of Skanska Infrastructure Development, says half of U.S. megaprojects now are using some form of P3. "There's been a lot of learning, good and bad. DOTs know what they're getting into now," he observes.

And more agencies are getting into the idea of availability payments, says Patrick Harder, principal with Nossaman. "More agencies are looking at that structure to keep control of things that are politically sensitive, like toll pricing," he says, citing Florida's I-595 project. "The other thing is the value of certainty of maintenance."