Connecticut's residential coastline is two worlds, the one of newcomer millionaires and one whose wealth and New England roots span generations. Now, their differences over a rail route threaten to gum up plans for the U.S. Northeast's fastest-ever trains.

About 30 miles from Manhattan, hedge funds such as Bridgewater Associates and Tudor Investment Corp. and Fortune 500 companies help make Stamford the busiest station in the wealthiest state for Amtrak's Acela Express. Boardings are 47 percent lower toward the east, where century-old estates overlook the Long Island Sound and the Ivy League's Yale University has educated scholars for 300 years.

With the national railroad preparing for even faster Acela service between Boston and Washington, however, some of those towns are in the cross-hairs of a Federal Railroad Administration proposal for a 50-mile (80-kilometer) bypass designed to reduce curves and choke points. The plan, one of three under consideration, was so unpopular among residents that a group of lawmakers, including Democratic Sen. Richard Blumenthal, last month threatened to tie themselves to the tracks.

Skepticism is thick in Old Saybrook, home to Connecticut's first governor, where legend holds that the late actress Katherine Hepburn recovered her family's silver service from the beach after a 1938 hurricane leveled the estate. From that town northeast to Kenyon, Rhode Island, passengers would zip among farmlands, ecologically fragile waterways and historic sites.

"Nobody's against bigger, faster, more efficient rail," said Carl P. Fortuna Jr., 53, who is the first selectman, or mayor. "We're happy to help support your goal here. But not the way you're drafting it."

Asia and Europe have enjoyed high-speed rail since the 1960s, and Shanghai's magnetic-levitation train that rockets along at almost 270 mph started commercial runs in 2010. Japan, testing its next-generation maglev last year, hit a world-record 375 mph.

In the U.S., though, Democratic President Barack Obama, who included $8 billion for rail in his 2009 stimulus bill, has been stymied on widespread fast rail, one of his signature issues.

A Los Angeles-to-San-Francisco bullet train's projected cost of $33 billion has more than doubled. Texas Central Railway, which would use Japanese technology to run at 200 mph, has yet to raise $12 billion in private investment. And in Florida, where Republican Governor Rick Scott in 2011 refused $2.5 billion in federal rail money, a would-be private operator has struggled to sell bonds for Orlando-to-Miami service.

For fast rail, that leaves only Acela, operated by the government-subsidized Amtrak, running 457 miles between Boston and the nation's capital. In 2021, Amtrak is to introduce the first of 28 new Acela trains, to be purchased with a $2.45 billion federal loan that's the largest in U.S. Transportation Department history.

"Amtrak is taking the necessary actions to keep our customers, the Northeast region and the American economy moving forward," Joe Boardman, the then-Amtrak chief, told reporters in Wilmington, Delaware, on Aug. 26, when Vice President Joe Biden announced the agreement. "These train sets and the modernization and improvement of infrastructure will provide our customers with the mobility and experience of the future."

Though the new fleet will be designed to hit 186 mph -- up from a maximum of 150 mph now -- planners first must upgrade sections of the Northeast Corridor, which runs through some of the nation's densest population centers and has few of the straightaways necessary for the world's fastest trains. Even today's Acela is overpowered, with the full force of front and rear locomotives kept in check, according to Jim Cameron, 65, of Darien, founder of the Commuter Action Group, which represents rail riders in the New York City suburbs.

"There's no way you could ever achieve high-speed, world-class service with the right-of-way we have today," Cameron, a frequent Acela passenger, said by telephone. "This train is like a Ferrari driving on a dirt path."

In Old Lyme, across the Connecticut River from Old Saybrook, about one in four residents signed a petition objecting to the bypass, which at one point involved elevated tracks through the downtown, a backdrop for the 19th century American Impressionist movement. That design has been scrapped.

"We have committed to the Old Lyme leadership that if the final blueprint includes the bypass in that area, it would NOT be an aerial structure through the historic district," Matthew Lehner, a railroad administration spokesman, said in an email. Officials are talking about a tunnel instead, where the Connecticut River meets the Long Island Sound, according to First Selectwoman Bonnie Reemsnyder.

"Even with a tunnel, you have venting, and that has to come out somewhere, and you have vibrations," Reemsnyder, 62, said by telephone. "It's already had a negative effect on house sales. A line on the map already has done this community damage."

Though Lehner said federal officials will make their recommendations later this year, documents obtained under the Freedom of Information Act by activists suggest that the bypass emerged as the favored among the three proposals before all public hearings had taken place.

"They have the maps already decided 10 months ago," said Gregory Stroud, executive director of SECoast, a southeastern Connecticut non-profit preservation group. "Do I believe that the public has been misled? Absolutely."

The railroad administration says the proposals aren't just for Acela, but for regional and commuter trains on the Northeast Corridor, the nation's busiest passenger line. A wish list of improvements for the route's entire length, plus construction of a second, parallel line, would cost $290 billion, according to the government-run website NECfuture.com.

In Stamford, whose railroad station draws Amtrak riders from such enclaves as Greenwich, New Canaan and Westport, the population has grown 8 percent, to 129,000, in the past five years, according to Thomas Madden, 43, the city's director of economic development. Commercial space and 8,000 apartments are under construction, he said, at a cost of $6 billion.

"It really does help the Fortune 500 companies, and the other companies, to serve the businesses on the Northeast Corridor," Madden said of Acela. "We're pushing for faster rail both on the Metro-North line and for Amtrak."