TSURU, Japan -- With a slight jerk and a high-pitched whine, the world's fastest train accelerates from a standstill so quickly that the excited passengers are pushed deep into their seats.
Reaching 310 mph takes less than a minute and a half for Japan's maglev train - which derives its name from its use of an electromagnetic cushion instead of wheels for levitation and propulsion. Officials point to the high-tech showpiece as the future of mass transit.
But after four decades and $2.4 billion spent on research, the maglev has just one station, no ticket booths - and no clear future.
"We want to build the line as soon as possible," said Yutaka Osada, deputy chief of Central Japan Railway Co.'s maglev research division. "But the government has to decide because it will pay to start construction. With the current economy, it probably won't be running for some time."
Skeptics say the maglev may never travel beyond its 11.4-mile test track in Tsuru, west of Tokyo.
They say prestige, not pragmatism, drives the project.
Experts concede that the trains aren't greener than existing electric-railway technology, notably the Shinkansen "bullet trains" that traverse the mountainous countryside and connect major cities at up to 186 mph. Japan also uses monorails, trains and subways for intra-city transit.
"The maglev is less efficient than the Shinkansen. It consumes about three times more energy," said Satoru Sone, an engineering professor at Tokyo's Kogakuin University.
But Sone said the maglev could someday replace airplanes for shuttling passengers around Japan because they emit one-fourth of the harmful greenhouse gases of a passenger jet.
"Bullet trains are too slow to compete with planes. But the maglev might one day replace domestic air travel along some routes," he said.
In December, Central Japan Railway, part of the former state-run railway that is jointly developing the maglev with Japan's Railway Technology Research Institute, said a three-car maglev sped to 360 mph, surpassing its own Guinness World Record of 342 mph with passengers aboard, set in 1999.
Few countries have poured as many resources into maglev development.
China began daily runs of the world's first commercially operated maglev on Jan. 1, but the $1.2 billion German-built system in Shanghai spans only 18 miles. Earlier plans for an 800-mile Shanghai-to-Beijing line were canceled.
Germany, meanwhile, has scrapped plans for its own line between Hamburg and Berlin.
A maglev project in the United States is still in development. A company called American Maglev Technology Inc., in Edgewater, Fla., is working with Virginia's Old Dominion University, which hoped to start shuttling students across campus on a maglev last fall. But the project was delayed a year ago when technical glitches surfaced and $14 million in public and private funds ran out before they could be fixed. (Old Dominion has been awarded $2 million in federal money to finish the project, but the university and American Maglev face lawsuits filed by three contractors who worked on construction).
In this country, Central Japan Railway officials say the long distance that Japan's maglev would travel justifies its enormous price tag. The company wants to build a maglev line from Tokyo to Osaka, linking the two nation's largest cities in just one hour, the same as commercial flights. Its bullet trains require 2 1/2 hours to make the 310-mile trip.
In April, a government panel of experts applauded the progress. But the experts said the project's costs are still too high, and said they would reassess the situation in 2005.
Building the train's electromagnetic guideway could set back taxpayers $85 billion, or roughly $274 million per mile of track. That's three times what it costs to lay bullet-train tracks. Maglev trains would tack on another $6.48 billion.
The technology is certainly cutting edge.
To float 4 inches above its tracks, the maglev is equipped with superconducting magnets that must be cooled to around minus 500 degrees Fahrenheit. Researchers are working on a cheaper, superheated version.
The concrete guideway, crammed with power cables, sensors and two types of magnets, is smooth and safer than rails during an earthquake. Tunnels are shaped like a horn to keep the shock waves of a speeding train from shattering windows on nearby buildings.
Central Japan Railway's Osada says his team is simplifying and miniaturizing track and train parts to make mass-production and maintenance cheaper. A new lead car with a flatter, elongated nose also has cut air resistance, which produces noise and turbulence.
The maglev's safety record is sterling. It has traveled more than 207,000 miles - equal to eight times around the globe - and carried nearly 70,000 people in tests, without an accident.
There's almost no danger of derailing because the guideway walls are half as tall as the train. In a power outage, inertia and magnetic forces would carry the train to a gradual stop. Air-flap brakes like those airplanes use and retractable wheels would be deployed in case of magnetic failure.
But the ride is still more roller coaster than mass transit: exhilarating and bumpy. It's also noisier inside than on bullet trains.
Yuuki Uete, 31, who came to Tsuru from Japan's central Gifu prefecture with her husband and two sons to ride the maglev on its brief test run, said she hoped to eventually take a trip on a long-distance, commercial maglev.
"It was a bit scary because it shook more than I thought it would," she said. "But I hope someday we will ride the real thing."