When John Adams traveled between Boston and Philadelphia in 1776, it took him two weeks.

On Amtrak's Acela today, the trip is about five hours. But sometimes, the train seems as frustratingly slow as Adams' horse.

Poking through North Philadelphia, lumbering out of New York City, wallowing through Bridgeport, America's high-speed rail is anything but.

Compared with its cousins in Europe and Asia, Amtrak's showcase service is heavy and slow, less a bullet train than a cannonball on wheels.

The 319-mile trip to Boston on Acela's 6:30 a.m. train out of 30th Street Station last week took 5 hours, 24 minutes; including stops, that worked out to an average speed of just 59 m.p.h., only slightly faster than driving.

The return trip was a little faster - 64 m.p.h.

By contrast, a high-speed train in Spain, from Madrid to Barcelona with a stop in Zaragoza, covers 385 miles in 2 hours, 52 minutes. That's 135 m.p.h.

High-speed rail has gotten renewed attention this month in the United States, as Amtrak unveiled its updated vision for 220-m.p.h. trains along the Northeast Corridor, California approved the first funding for bullet trains between San Francisco and Los Angeles, and Philadelphia hosted the first international congress on high-speed rail held in this country.

"We are committed, because of the president's vision, to high-speed rail in America," U.S. Transportation Secretary Ray LaHood told world rail leaders here.

"We are going to continue to make progress," he said, with special emphasis on the Northeast Corridor.

But the trip from Philadelphia to Boston shows the gap between LaHood's vision and today's reality. And it illuminates the obstacles that Amtrak - or any rail operator - faces in bringing European-style fast trains to the United States.

Tracks aren't straight enough. Overhead power lines are old and sagging. Local commuter and freight trains get in the way. Old bridges, outdated tunnels, and road crossings force delays.

Even though Acela trains are built to operate at 150 m.p.h., they can rarely reach top speed. Only along a short stretch through Rhode Island and Massachusetts can Amtrak engineers open the throttle. Between New York and Washington, the best they can do is 135 m.p.h.

And for 59 miles between New Rochelle, N.Y., and New Haven, Conn., Acela trains are constrained by 75-m.p.h speed limits set by Metro North, which owns that stretch of track.

"We lost a little time here getting into New Haven," the conductor announced as Acela 2150 left that city last week. "It looks like you'll be a wee bit tardy getting into Providence."

Such delays are not unusual. Acela 2150 was late 15 percent of the time last month, and Acela 2165, which we took from Boston to Philadelphia last week, was late 29 percent of the time in June.

By contrast, passengers on Spain's Madrid-to-Barcelona route get their money back if the train is more than five minutes late.

Acela travel is not cheap: One-way tickets between Boston and Philadelphia range from $125 to $250, depending on time of day and advance purchase.

And the amenities are, well, pedestrian: The free Internet service was inoperable on Train 2150, and the overhead digital displays provided only canned messages like "See Something, Say Something." In the club car, the attendant was using Super Glue to try to repair his handheld receipt dispenser.

Unlike the sleek high-speed trains of Europe and Asia that resemble aluminum birds, the Acela is a steel tank, built to survive collisions in the mixed-use environment of the Northeast Corridor.

"We had to cope with the FRA [Federal Railroad Administration] crash standards," said Francois Lacote, senior vice president/technical for Alstom Transport, the French train-builder that made the Acela for Amtrak along with Bombardier, a Canadian firm. "It's much heavier, it's totally different."

The 308-passenger Acela weighs 1.2 million pounds, twice as much as Alstom's 300-passenger, 600,000-pound AGV train.

"If you want to go fast, you need light trains with no curves [on the tracks]," said George Mekosh, product manager for Bombardier Transportation/North America. "And you can't have a station stop at every congressman's hometown."

True high-speed trains run on dedicated tracks, free of conflicts with slower commuter trains and heavier freight trains.

On the Northeast Corridor, however, about 2,200 trains operate every day in close quarters, including those owned by Amtrak, transit agencies such as SEPTA and Metro North, and freight railroads.

Money, of course, is Amtrak's biggest obstacle.

Billions worth of much-needed maintenance and improvements on the Northeast Corridor have been postponed for decades, and government-subsidized Amtrak staggers from year to year with its federal funding never certain and often endangered.

Despite all that, Acela is a success.

It carries 3.6 million passengers a year and produces 25 percent of Amtrak's total ticket revenue with just 10 percent of its ridership.

It makes money, earning $550 million in revenue on operating expenses of $360 million.

Trains are often sold out, and Acela averages 80 percent capacity on its busiest segments.

And it is beating the competition: Since Acela started operating in 2000, Amtrak's share of the airline and rail market has grown from 37 percent to 75 percent between New York and Washington and from 20 percent to 54 percent between New York and Boston.

"The train is more reliable and faster than flying," said Bobby Burchfield, a Washington lawyer who boarded Train 2165 in New York and travels frequently between the two cities. "I don't have to deal with security at the airport. . . . I can get right on the train, and the train delivers me right downtown."

"I can work on the train," Burchfield said, immediately powering up his laptop and using his cellphone to join a conference call. "And last time I checked, flying was twice as expensive."

To meet growing demand, Amtrak wants to buy 40 more Acela passenger cars by 2015, expand each of its 20 Acela trains from six cars to eight, and increase seating capacity 40 percent - 130 more seats per train.

And by 2020, Amtrak proposes to buy new trains to double Acela frequencies between New York and Washington.

To allow trains to go faster, Amtrak is spending $450 million to improve the Northeast Corridor main line between Trenton and New Brunswick, N.J. That will increase maximum speed for Acela trains on that 24-mile stretch from the current 135 m.p.h. to 160 m.p.h. by 2017.

Amtrak's long-term, $151 billion vision is to build a dedicated route for 220-m.p.h. trains as part of an upgraded Northeast Corridor. That would allow 37-minute trips between Philadelphia and New York, 94-minute trips between New York and Washington, and 2½-hour trips between Philadelphia and Boston.

For passengers such as Melissa LaReau, an international tax-services employee of accounting firm Ernst & Young, faster trains would be worth the cost.

"I'd be willing to pay more," said LaReau, who was returning to Washington from New York. "Time is valuable. If something gets you there faster, it's worth the price. You could spend more time with a client and be more productive."

"A tax would be worth it," she said.

Congress remains unconvinced. The recently approved federal transportation budget included no money for rail, leaving Amtrak to the traditional vagaries of annual appropriations.

The Obama administration spent $8 billion in stimulus funds on high-speed rail in 2009 and urged Congress to authorize about $10 billion a year for the next six years. Facing record federal deficits and deep partisan divides, Congress instead approved no additional funding.

So the Acela chugs along, gaining riders if not speed, as the closest thing America has to high-speed rail.

"Until the last two years, the United States has spent very little on intercity passenger rail compared to other countries and to other transportation modes such as highways and aviation," Amtrak vice president Stephen Gardner told a House subcommittee last year.

"As they say, you get what you pay for."

See a video about riding what passes for high-speed rail in the Northeast Corridor at www.philly.com/acela