How viable is a U.S. high-speed rail system?

Why doesn't the U.S. have its own extensive high-speed passenger rail system?

Other countries have long been building out their high-speed trains. Japan's famed bullet train, or Shinkansen, is celebrating its 50th anniversary this month. That rail system was credited in part with helping to revive Japan's post-war economy. And a Japanese rail operator recently tested a new magnetic levitation (maglev) train that can reportedly reach speeds of over 300 miles per hour.

Meanwhile, China and Russia are weighing whether to build a high-speed rail line that would connect Moscow and Beijing and stretch 4,350 miles long.

There are some American examples: Amtrak's high-speed Acela Express service, which runs between Boston and Washington, D.C., is doing steady business. California also has plans for a high-speed rail link between San Francisco and Los Angeles, although that project has become bogged down in funding, legal and political issues.

A report issued last year by the Brookings Institution described American passenger rail as undergoing a revival, with Amtrak ridership at "record levels and growing fast." The result, the report said, is a "new federalist partnership where Amtrak, the federal government, and states share responsibility for the network's successes and failures."

But Michael Smart, an assistant professor of urban planning at Rutgers University, believes America's car culture continues to create obstacles for U.S. passenger rail service, high-speed or otherwise.

"Even if we do provide some kind of high speed rail service, driving still remains extremely convenient, it remains relatively cheap," he said.

And even while passenger rail services are growing in some parts of the country, a dramatic increase in freight train traffic -- prompted by the rise of oil transport by rail from shale oil fields in the Plains states and Texas -- is interfering with efforts to further develop those passenger rail networks.

Another issue is whether those proposed high-speed rail corridors will live up to their financial expectations.

"A lot of the projections about how cost-effective passenger rail is are based on full trains," Smart said. "And we don't really know if a lot of these trains that are being proposed will be full or not."

For the moment, high-speed rail appears to have the most promise in high-population regions of the U.S., places where passenger trains are considered a welcome alternative to traffic-snarled highways and airports.

And overseas investment may eventually come riding to the rescue of the high-speed rail industry. Last month, an investment group announced it has lined up a $5 billion commitment from the Japan Bank for International Cooperation for a proposed high-speed maglev system along the Northeastern Corridor.