The passenger rail service isn't running trains on that route between 4 p.m. Saturday through noon Sunday while two century-old spans are being replaced on the East/West Harbor Bridge in Stonington, Conn.
Amtrak's Train 135 from Boston's South Station will be a few minutes early Saturday afternoon between Boston and Old Saybrook, Conn.
Amtrak says no alternate transportation is being provided and passengers are urged to take earlier or later trains, or book with private bus services.
Local commuter services and Amtrak's shuttle between New Haven, Conn., and Springfield aren't affected.
The $22.1 million project has been under way for more than two years.