Interest in the nation’s infrastructure is rising to a level not seen since the debate over the Interstate Highway System in the 1950s. Propelled by the prospects of a deep recession, President-elect Barack Obama is pressing for major new federal spending to boost employment. He is committed to a major new economic stimulus, including potentially hundreds of billions of dollars for the nation’s roads, highways, airports, ports, and transit systems.

Keynesian ideas have received a new lease on intellectual life. Prominent economists, including New York Times columnist Paul Krugman, have exhorted the new president to be bold. Krugman is calling for a stimulus package of $600 billion or more.

Infrastructure spending is slated to play a central role in this government-activism effort to jump-start the economy. In theory, this makes sense: Infrastructure is a “hard” asset and it’s crucial to economic growth. With new composite materials and engineering techniques, the bridges and roads we build now could be around for centuries, not just decades.

Construction jobs are also high paying, on average — $22 per hour, as opposed to the national average of $18. According to the new Keynesians, these jobs will therefore be especially helpful to the overall economy, by dumping millions of dollars into the hands of consumers.

Proponents believe that this infrastructure spending will also be very useful through its direct creation of jobs. The American Association of State Highway and Transportation Officials (AASHTO) claims that every billion dollars spent on infrastructure creates 35,000 jobs. A $50 billion spending spree would, based on this estimate, produce 1.75 million jobs. That would more than make up for the number of jobs that are expected to disappear in 2009.

Unfortunately, this optimism is based more on faith than on experience. In fact, infrastructure spending is a lousy way to bring a globally competitive services-based economy out of recession. One reason should be obvious: America’s economic base is not founded on construction workers and their supervisors. It’s no longer dependent on the rote assembly-line work that made the U.S. manufacturing economy the envy of the world. Since 1980, the U.S. manufacturing sector has shed 5.5 million jobs — but the overall economy has added 50 million service jobs.

America’s economic future lies in creating large numbers of jobs in advanced services, high-tech manufacturing, and information technology. The 75,000 workers who face losing their jobs as Citigroup pares its payroll to stay solvent won’t be looking for work rebuilding and repairing the nation’s highways. And they shouldn’t. Their economic future lies in a dynamic, growing, and innovative financial-services industry that can compete globally.

This is not to say that infrastructure needs should be neglected in policymaking. Quite the opposite: A wealthier people values mobility, and is willing to pay for the technology and public services necessary to get from point A to point B faster. It is willing to devote a larger share of its income to obtain these higher service levels. Currently U.S. families spend about one-fifth of their income on transportation. Joel Schwartz, an analyst with the American Enterprise Institute, notes that automobile ownership — the major source of modern-day mobility — also increases with income. “In a wide range of economic, policy, and cultural contexts,” he says, “people the world over choose automobiles for travel and suburban living as soon as they become wealthy enough to afford them. Wealth is the single greatest determinant of automobile ownership and driving.” This is true even in nations where cars (and gasoline) are taxed at high levels.

These auto owners are willing to spend a lot — but they spend carefully. And they are right to worry that the government does not show equal care in how it spends transportation dollars. Research increasingly shows that our investment in traditional infrastructure isn’t getting the bang for the buck it once did.

In the mid-20th century, the need was clear: connect our urban areas, provide high-speed freight corridors for goods shipment, and get workers to their jobs (often in downtowns). We created the “hub and spoke” urban highway network as a result, and it worked. By knitting together the nation’s major urban areas, the federal infrastructure investment reduced shipping costs and made commuting much easier, thus dramatically improving productivity. Cliff Winston at the Brookings Institution estimates that the rate of return from highway investments to business during the heady days of the 1960s and 1970s approached 15 percent.

Since then, however, the effectiveness of infrastructure spending as a way to boost productivity has declined dramatically. Why? The short answer is that we no longer live in the 1950s.

Look at contemporary American travel patterns. Suburb-to-suburb commutes, notes Alan Pisarski in Commuting in America III, now account for the largest share (46 percent) of overall commuting. Traditional suburb-to-central-city commutes make up just 18.5 percent of the total.

Even more telling, “pure” commuting trips — those that involve a straight shot from home to work — make up less than one-fifth of overall commuting. Most trips are combined with other trips, “chained” with dropping kids off at daycare, running to the store or drycleaner, or even meeting clients outside of a normal workplace.

More broadly, the largest single category of all travel, constituting 42 percent of the total number of commuting and non-commuting trips, is “other.” In short, our travel patterns have become so dynamic, complex, and customized that we can’t even categorize them in a meaningful way.

We’ve already captured the low-hanging fruit with the existing network. Our immediate challenge now is to maintain the system and enhance it in economically meaningful ways. That’s not cheap. Our nation is underfunding its existing infrastructure to the tune of at least $80 billion per year. We need to be spending at least $125 billion per year on roads, highways, airports, and ports just to tread water on economic productivity.

Our competitive challenge is to invest in the right infrastructure in the right place and at the right time. A major infrastructure-spending program initiated in the heat of a “crisis” will not bring the benefits of a well-planned overhaul of our transportation networks. New infrastructure spending has to be prioritized in such a way that the economic benefits are both transparent and meaningful. Simply parachuting dollars into the economy won’t generate the benefits our economy needs and may confound efforts to put us back on the path toward economic sustainability.

Fortunately, we have the tools and the incentive to embrace the innovation necessary to reestablish the U.S. as a world leader in infrastructure investment. Many of President-elect Obama’s transportation advisers are poised to embrace many of these innovations, if they are appointed to key posts in the administration.

Central to the reform efforts will be an expanded role for technology and the private sector in providing new, high-quality infrastructure. Hundreds of billions of dollars are available worldwide for infrastructure investments in the U.S., an unintended but happy side-effect of the “flight to quality” brought about by the collapse of world financial markets. As traditional financial products are curtailed, investors are still looking for profitable investments, and transportation-infrastructure investment is a leading contender.

Improvements in technology make it easier for us to tie use of a road to payment for the road. We can now do electronic toll collection with no stopping at tollbooths. The technology gives us the ability to change the toll in accord with the volume of traffic, which helps us match price to demand and reduce congestion; and it gives road managers better information on which roads need quality improvements.

Travelers on the 91 Express Lanes in Orange County, Calif., and high-occupancy toll (HOT) lanes in Minneapolis, San Diego, Denver, and Houston are already experiencing this newfound efficiency, and the economic benefits of 21st-century highway technology and management. Similar innovations will be improving the travel experience for (and increasing the productivity of) travelers in Washington, D.C., and Atlanta in the near future.

Experience in China, Australia, India, France, Spain, and elsewhere has demonstrated the importance of letting the private sector take the lead in proposing, developing, and implementing these solutions through long-term agreements with governments called public-private partnerships (PPPs). The federal government will also have to embrace the experimentation already occurring in the states — and resist temptations to reinvigorate an overbearing federal presence that is more interested in centralizing its power and consolidating its political turf than in creating a truly competitive, modern transportation network.

Transportation policy may be one area where an Obama administration will leave a positive legacy for the nation and its cities. While Republican governors such as Rick Perry in Texas and Mitch Daniels in Indiana have staked out ambitious and politically courageous positions supporting PPPs, Democratic innovators include former Philadelphia mayor and Pennsylvania governor Ed Rendell, Chicago mayor Richard Daley, and Denver’s mass-transit innovator, Cal Marsella.

The alternative is federal retrenchment that harkens back to Depression-era thinking about transportation policy and economic stimulus — and that would put the nation at serious risk in a globally competitive economy. Policymakers on both sides of the aisle will need to pay attention to these global economic realities and the way mobility enhances productivity, as they chart a new federal role for guiding infrastructure investment in 2009 and beyond.