Although so-called bullet trains in France can travel at speeds approaching 575 kilometers per hour, their adoption in the U.S. has been more local than express. Now, 140 years after the transcontinental railroad's nearly 2,900 kilometers of track first connected both U.S. coasts, a number of states are hoping for a second golden age of rail, this time fueled by the Obama administration's pledge of billions of stimulus dollars for high-speed railway development.

California is developing perhaps the most ambitious high-speed rail plans, a project that would include a mixture of shorter lines connecting Los Angeles to Anaheim and San Francisco to San Jose as well as a longer line traversing the nearly 1,300 kilometers between San Francisco and San Diego (with a branch through Sacramento). The $10-billion price tag to get these projects on track is equally ambitious—California is looking for $4.7 billion of this to come from the $8 billion in stimulus money the federal government is making available for high-speed rail projects under the American Recovery and Reinvestment Act.

The San Francisco-to-San Diego high-speed line alone is expected to cost at least $45 billion by the time it is finished. With trains allowed to run in excess of 320 kilometers per hour on some stretches, state officials estimate a trip between Los Angeles and San Francisco could take as little as two and a half hours. Anaheim Mayor and High-Speed Rail Authority Board Chairman Curt Pringle has said that the state could break ground on its high-speed rail projects before 2012.

Other states, including Florida and Texas, are proposing to build dedicated high-speed rails from scratch that would allow trains to reach top speeds of about 240 kilometers per hour. The Obama's administration's "Vision for High-Speed Rail in America" report (pdf) released in April identifies 10 potential high-speed corridors for federal funding. In addition to California, Florida, New York State and New England, these include locations in the Pacific Northwest, Midwest, Southeast, Gulf Coast and Pennsylvania.

The administration's rail report does not spell out exactly how many of these high-speed corridors will be include new tracks exclusively for use by faster trains, as opposed to tracks shared with freight and slower passenger services. Amtrak's Acela service is the only passenger train line in the country that has exceeded the 177-kilometer-per-hour speed necessary to earn the U.S. Department of Transportation's "high speed" classification. The Acela is able to reach about 240 kilometers per hour along small segments of its route from Washington, D.C., to New York City and on to Boston, but because Acela runs on tracks shared with lower-speed passenger and freight trains it still only averages 109 kilometers per hour. Changing this is an expensive proposition, reported last month. Cutting just 15 minutes off the 354-kilometer route between New York City and Washington would cost an estimated $625 million, and shortening the trip an additional 15 minutes could cost as much as $5 billion.

Several factors complicate the U.S.'s high-speed rail goals. These include a shrinking pool of in-country rail sector experts (which the Obama administration acknowledges is the result of the relatively small investment in passenger rail in recent decades), a lack of money available at the state level for such projects, and the need for safety standards specific to high-speed trains. The administration pointed out in its report that whereas most high-speed systems overseas have a good safety record, they usually operate on dedicated tracks.

But building the infrastructure necessary for a dedicated high-speed rail is no small job, taking into account the special safety requirements these train lines require, says Raj Rajkumar, a professor in electrical and computer engineering at Carnegie Mellon University in Pittsburgh. This includes running tracks above or below roadways to avoid railroad crossings and fencing off areas to avoid collisions with animals, people and road vehicles. Given the increased centrifugal force created by the high speeds around curves, it is also advisable to increase the height of embankments around curves and widen the track gauge to prevent derailments. "The $8 billion is a lot of money, but it costs a lot more to build out the infrastructure," he adds. Despite the existence of Amtrak's Acela, "you don't have an existing high-speed train industry in the United States to build upon."

Dedicated tracks are important to the development of high-speed railways. For one, high-speed trains are more sensitive to changes in their rails, which means it is not a good idea for them to share their lines with heavier freight trains that can warp the tracks, says José Holguín-Veras, a professor of civil and environmental engineering at Rensselaer Polytechnic University in Troy, N.Y. Although the Acela shares tracks with slower-moving passenger and freight trains, "sharing rails between high-speed and freight won't work" if fast trains are introduced and traffic is increased.

"High-speed rail has an important role to play in the United States, particularly for the mid-range distances of 100 to 500 miles," (160 to 800 kilometers) Holguín-Veras says. "In that range high-speed could compete quite favorably with air travel."