The Obama administration will weigh 15 alternatives for improved passenger rail service between Boston and Washington, ranging from modest upgrades to a new high-speed Northeast Corridor that would allow trips between Philadelphia and New York City in about 40 minutes.

The 15 "preliminary alternatives" were unveiled Tuesday by the Federal Railroad Administration.

The FRA plans to come up with a single "preferred alternative" by mid-2015, complete with cost estimates and possible construction schedules.

The goal is to lay out a feasible plan for investing in the nation's busiest rail corridor through 2040, with proposals for updated equipment, more trains, new stations and possible new routes.

Without an infusion of money to revamp the overcrowded, outdated corridor, the Northeast's economic future will be stifled, the FRA said. The region now generates 20 percent of the country's gross domestic product.

The 15 alternatives presented were broad concepts, long on generalities and short on specifics.

They fall into four categories, A through D, that could be characterized as "good," "better," "best," and "visionary." Within each of the categories, three or four possibile alternatives were offered.

The least ambitious of the alternatives would make modest improvements to the existing 457-mile corridor to allow top speeds of 160 miles an hour and provide new express trains, similar to upgrades now being made by Amtrak. The fastest Acela Express trains now reach speeds of 150 miles an hour on a short segment of the corridor.

The most ambitious four alternatives propose a second NEC line dedicated to high-speed trains that could travel at 220 miles an hour and cut travel time between Philadelphia and New York City to about 40 minutes.

The four high-speed alternatives offer different possible routes between Boston and Washington.

One would parallel the existing route, but could mean new stations in Center City or at Philadelphia International Airport.

Another proposes a new route north of New York, through Danbury and Hartford, Conn., while another suggests a route through Long Island and under Long Island Sound to New Haven, Conn.

A fourth proposes a route that bypasses Baltimore, traveling instead through Annapolis and the Delmarva peninsula to Wilmington. North of New York, that route would go under the Long Island Sound and then north through western Connecticut and Massachusetts to Boston.

The FRA's study is broader than last year's proposal by Amtrak for 220-mile-an-hour rail service between Washington and Boston by 2040. That Amtrak plan calls for trips from Philadelphia to New York in 37 minutes, half the time of the fastest Acela Express trains now.

Amtrak's proposed $151 billion high-speed rail service may be considered by FRA planners as part of the solution, but FRA says it will consider other alternatives for high-speed travel, as well as new options for commuter and freight trains.

The current rail corridor, which handles more than 2,000 Amtrak, commuter and freight trains daily, suffers from major congestion and delays, and "many components of the system are in a state of disrepair or, worse, have reached the point of obsolescence," the FRA says.

The FRA will seek ways to increase capacity, boost train speeds and reliability, while adding service along the main route and on feeder lines such as the Keystone Corridor linking Philadelphia and Harrisburg.

The next step on the way to a preferred alternative is a series of public meetings next week in New Haven, Newark, and Washington.