The Long Island Rail Road will have extra trains on standby Friday night at Penn Station in case they are needed to carry travelers back to Long Island at the end of the papal Mass at Madison Square Garden, the railroad said Wednesday.

The LIRR had previously announced it would operate eight extra westbound trains Friday on the Babylon, Port Jefferson and Ronkonkoma branches for the papal visit.

Officials said people using subways and commuter rail lines should buy round-trip tickets or MetroCards in advance and expect some crowding. The officials said they would adjust subway operations if needed at stations near papal events and would have additional customer service representatives on duty at those stations.

The changes are an attempt to cope with traffic and commuting for the next few days as the Big Apple welcomes Pope Francis and the United Nations General Assembly at the same time.

A Giants football game at the Meadowlands Thursday night and baseball games at Yankee Stadium Thursday and Friday should add to the congestion.

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Street closings began Tuesday around the United Nations and on the FDR Drive, and will continue through Oct. 2, although some streets closed during the day will be open to traffic at night.

Pope-related closings begin Thursday in the area around St. Patrick's Cathedral in midtown and later in the day around the papal nuncio's residence on East 72nd Street.

There will be further closings Friday as the pope visits the National September 11 Memorial & Museum in lower Manhattan and an East Harlem school. He then motorcades through Central Park on his way to Madison Square Garden, where he will celebrates Mass at 6 p.m.