Federal planners have refined their choices for the future of the Northeast Corridor's passenger rail service, but have not attached cost estimates to any of the alternatives, from minimal service improvements to an entirely new high-speed corridor between Washington and Boston.

The "NEC Future" planners will be in Philadelphia this month to discuss the plans and the process with the public.

The four broad alternatives outlined by the Federal Railroad Administration this week were the latest steps in planning for upgrading the corridor over the next 25 years.

A final proposal, including estimated costs and construction schedules, is to be released by late 2016, after environmental-impact studies are completed, project manager Rebecca Reyes-Alicea said Thursday.

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Without an infusion of money to revamp the overcrowded and outdated corridor, the Northeast's economic future will be stifled, the FRA said.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.

Any action to implement the FRA's plan would require approval and financing from Congress.

Although the FRA has not made any cost estimates yet, Amtrak has said it would require more than $10 billion to simply restore the rail corridor to a state of good repair. Also, $151 billion would be needed to develop a separate high-speed corridor between Washington and Boston to accommodate trains traveling at 220 m.p.h. and cut the travel time between Philadelphia and New York to 37 minutes.

The alternatives outlined this week by the FRA are:

No action. A "substantial" increase in maintenance and renewal spending from current levels, just to continue today's service in the 457-mile corridor through 2040.

Alternative 1. New rail service to keep pace with population growth, doubling train service and tripling the number of seats. Would include a new tunnel under the Hudson River with two additional tracks for service to and from Manhattan. It would not provide "meaningful travel-time improvements."

Alternative 2. New service and route improvements to grow rail service faster than the population. The entire corridor would have at least four tracks, with six tracks in New Jersey and southwestern Connecticut. A new downtown station in Philadelphia, with a stop at Philadelphia International Airport. (30th Street Station would continue to serve regional trains.)

Alternative 3. "Transformative" improvements, including a second high-speed route that would parallel the existing corridor south of New York City and take a new route north of New York. Would position rail "as a dominant mode for intercity travelers and commuters across the NEC."

The options are being developed to give the public and policymakers enough information to decide what rail service they want and how much they are willing to spend to get it, Reyes-Alicea said Thursday.

"Reliability is a key piece, and we struggle with that today," she said. "Down the road, we are going to have to throw in an element of cost, so we can determine what we're willing to invest in."

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, and have reached the point of obsolescence," the FRA says.

The FRA is holding a series of "open house" meetings this month in major corridor cities.

The Philadelphia session will be from 4 to 7 p.m. Nov. 19 at SEPTA headquarters at 1234 Market St.

The full report on the preliminary alternatives is available at http://www.necfuture.com/