As a result, virtually all regularly scheduled Amtrak service ­ including Acela Express trains -- will operate Saturday and Sunday, June 14 and 15 throughout the New York-Boston region, Amtrak said.

“Because of the shift in plans, Amtrak has scheduled additional Boston-New Haven-New York Inland Route trains and some connecting bus service to bypass the bridge outage during the four-day period from June 16 through June 19,” Amtrak said in a release.

“On the positive side, we were pleased to note that Amtrak has made some arrangements for extra Boston-New York trains via the “Inland Route” through Hartford, Springfield, and Worcester, and for “bustitution” service, said NCI President James P. RePass when informed of the delay. “We had hoped they would agree to do that, just in case the project runs longer than four days. The region's transportation network is too important to allow one segment to be completely out of service without some compensating transportation provided.” RePass credited work by ConnDOT Deputy Commissioner Albert Martin, and public statements by CT Gov. Jodi Rell for insisting on the bus-around plans, which Amtrak had originally refused to offer.

Amtrak's contractor on the job, a subsidiary of the worldwide URS Corporation, ran into what Amtrak called “unexpected difficulties,” in “Šdismantling the old draw span's massive concrete counterweight.”

After more than two years of preparation and construction, Amtrak will install a new vertical lift span to replace the movable bascule portion of the bridge, marking the final stage of a multi-year, $83 million project designed to improve the reliability of the bridge, reduce the chance of operational failures, and minimize train delays.

During the four-day bridge outage, Amtrak will also undertake numerous track and signal maintenance projects between New Haven and Boston to provide smoother and more reliable passenger rail service.

Amtrak apologized for any additional inconvenience resulting from the shift in plans.

For up-to-the-minute information on train and bus schedules during the outage, customers may check amtrak.com or call 1-800-USA-RAIL.

Here are the details of Northeast Corridor service as published by Amtrak Wednesday:

• All regularly scheduled Amtrak service will operate between New York City and Boston, including Acela Express trains, except for two late evening trains on Sunday.

• All Acela Express service is canceled north of New York City. (Acela will operate normally between New York and Washington.)

• Three Northeast Regional round-trips will operate between New York and Boston via Hartford and Springfield (the “Inland Route”), offering coach, business class and café service.

• Four daily round-trip express bus schedules will operate between Providence and New Haven, connecting with trains at those cities. These buses will operate express with no intermediate stops.

• Four daily round-trip express bus schedules will operate between Kingston, R.I. and New Haven, connecting with trains at those cities. These buses will operate express making no intermediate stops.

• Three round-trip trains will operate between New London, Conn., and New Haven, with an intermediate stop at Old Saybrook, Conn. These trains will connect at New Haven with other Amtrak trains to points west and south, and two of the three trains will accommodate Connecticut DOT monthly ticket holders.

• One round-trip train will operate between Westerly, RI and Boston, operating in the morning northbound and the evening southbound.

• During the bridge outage, while MBTA service to Route 128, Mass. will continue on a normal schedule, no Amtrak service will be provided from this station to points south, and passengers are directed to either Providence or Boston.

• During the bridge outage, no service will be offered at Westerly, R.I. to points west and south. Service is available at either Kingston or New London.

• Mystic, Conn., will have neither bus nor train service during the outage, and passengers should go to New London or Westerly.

• Because of substitute Inland Route service, New Haven-Hartford-Springfield Shuttle schedules will be changed and augmented.

• Regularly scheduled service resumes (except for train 95 and 171, which will have modified schedules.)

  During the bridge outage, Amtrak personnel and signs will be utilized to assist passengers with the adjusted schedules at stations along the Shoreline Route.

  MBTA and Shoreline East commuter rail service will not be affected by this bridge outage.