The historic visit this week by Pope Francis is expected to generate huge turnouts at multiple events in three cities, offering the chance for a once-in-a-lifetime spiritual boost for millions of faithful Catholics.
Some are also predicting an economic boost for the cities hosting the pontiff's visit.
With millions of the faithful expected to flock to dozens of public events in three major cities, organizers of the event say the pope's visit produce a windfall for area hotels, restaurants, event vendors and others. Philadelphia alone will see an estimated $418 million in increased economic activity, according the World Meeting of Families, which is organizing the pope's six-day trip.
But the events will also come with significant costs, including increased security, snarled local traffic and lost productivity. Adding up the net costs and benefits is an extremely difficult exercise.
That's why net economic benefits of large public events such as conventions or sports tournaments are often overstated, according to a 2008 study by economists at the College of the Holy Cross.
"While the conventional wisdom regarding national conventions is that they bring fame and fortune to host cities, our results suggest that any economic benefits are quite elusive," the authors wrote.
A lot depends on how many people actually show up, but organizers estimate several million people will make the pilgrimage, many of whom have signed up for tour packages that will bring an armada of buses to Washington, D.C., Philadelphia and New York City.
On the cost side of the ledger, one of the single biggest line items will be the cost of local crowd control, street closures, emergency services and security for event venues and the pope's safe travel along his itinerary.
Philadelphia officials have estimated out-of-pocket costs at roughly $12 million, with much of that needed to cover added services from the police and fire departments. Officials in New York and Washington have so far declined to provide cost estimates for city services.
But they are bracing for one of the biggest security challenges they've faced in a while. And local residents and businesses are bracing for epic traffic jams.
For the pope's Philadelphia visit, state and local officials plan to close 30 miles of highway in Philadelphia and New Jersey, and wave through only emergency vehicles and charter buses. They're also converting a major bridge from New Jersey into a pedestrian walkway and banning cars from driving on downtown streets closest to the events.
In New York City, the pope's itinerary will be accompanied by dozens of rolling street closures and a virtual lockdown of the areas around St Patrick's Cathedral, the papal nuncio, the United Nations and Madison Square Garden, which sits atop Pennsylvania Station, one of two main transit hubs that handles 600,000 commuters a day.