The price tag on an ambitious signal improvement on the PATH rail system linking New York and New Jersey is poised to rise, even as the system prepares to shut down its link to lower Manhattan for 45 weekends over the coming year.

The rising cost is being driven in part by a decision reached in December, shortly after a fatal Metro-North train crash in the Bronx, to ensure that the 21-mile PATH train system complies with a federal mandate to install anti-collision systems by the end of 2015.

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