(CNN) -   National Transportation Safety Board investigators
looking at the accident, along the corridor from New York to New
Haven, Connecticut, are focusing on a broken rail as a possible
cause for Friday's rush-hour collision.  "All of our teams have
been working around the clock to gather information and facts
that will help us determine what caused this accident and what
we can do to prevent it from happening again, Earl Weener of the
NTSB told reporters Sunday.   Amtrak released a statement Sunday
night saying that service between Boston and New Haven also
would be limited, and "there is no estimate on service
restoration." Because of that inconvenience, Amtrak said
passengers who "have paid but choose not to travel due to this
service disruption can receive a refund or a voucher for future
travel."    By Sunday afternoon, all the rail cars had been
removed from the accident site, said Weener. Two segments of
rail in the area of the fracture also had been removed and are
being sent to a laboratory for a