PHILADELPHIA (CBS/AP) — Crowds are forming early along Benjamin Franklin Parkway for another papal parade and an outdoor Mass, hours before the final events of the World Meeting of families are set to begin.

Visitors are already packed in as tight in the front of the viewing section as they were for the start of the Festival of Families on Saturday.

And long backups are occurring at security checkpoints.

It’s an early sign that the 4 p.m. Mass is likely to draw the biggest turnout of the pope’s U.S. visit.

SEPTA reports increased ridership on special papal trains heading into the city. More than 500 buses carrying 26,000 people had arrived by 11 a.m., nearly half of the shuttles organizers expect for the Mass.

Security officials are urging visitors to get to the checkpoints as early as possible to avoid last-minute bottlenecks.

An “unofficial estimate” by those working on the event places the number of people in the mass area around 860,000.

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