If the two million people the city is expecting to come here to see Pope Francis actually show up in September, Philadelphia will briefly become the third largest city in America, bested only by New York and Los Angeles. And there’s a chance the number could be even higher than that.

Mayor Michael Nutter, during a preliminary planning update Tuesday, said the city is expecting anywhere between one and two million people will make the trip into the city — whether they’re from Malvern or Milan — for the Papal visit on the weekend of Sept. 26. Added onto the 1.5 million residents, the number of people in this city won’t be far from the 3.9 million that live in LA.

Of course, Nutter and other city officials really have no good way of figuring out how many people will actually travel to Philly in 100 days for what he speculated could be, “the second or third largest event in United States history.”

“Everyone hasn’t called me to tell me that they’re showing up,” Nutter said Tuesday in response to a question about how officials are coming up with the one to two million number. “From a planning standpoint, we always have to anticipate the realistic possibilities.

“Given the popularity of Pope Francis, what we will have is a dynamic plan… that anticipates the unexpected and provides the necessary accommodations.”

It’s not unrealistic to think that even more than what’s been predicted could show up for the event. In 1979 when Pope St. John Paul II came to Philadelphia, crowds to see the Pontiff were estimated to be between 1.2 and 2 million people. As Plan Philly also pointed out, Pope John Paul II also held masses in New York City and Chicago. This time around for Francis’ first trip to America, he’ll also visit New York and Washington D.C., but Philadelphia is the only scheduled public appearance.

Francis has become a well-liked, albeit divisive, figurehead of the Catholic Church. In 2013, more than 3.5 million people showed up for the Pope’s first visit abroad to Brazil. The next year, 800,000 people showed up to see him in South Korea, a country where only 10 percent of the population is Catholic. (In America, it’s close to a quarter.)

Looked at another way, if more people than the city’s estimations show up here on Sept. 26 and 27 — say, 2.5 million — Philadelphia could briefly be the second largest city in the country, surpassing Los Angeles.

While city leaders play the guessing game, they’re working to figure out how to possibly accommodate such a high influx of visitors that will snarl traffic worse than the 2008 Phillies championship parade and the last Papal visit itself.

To do so, SEPTA is planning to run as many trains as it can to fewer stations — only 31 of its 282. PATCO, NJ Transit and Amtrak are bracing for huge numbers of travelers. The airport is planning for international passengers to crowd the area. Private cars won’t be an option. Basically, if you’re a resident, plan to walk everywhere, especially if you live within a three-mile radius of the Parkway.

Danielle Friedman, general counsel for 215-Get-A-Cab, said the city’s largest taxi company that has more than 800 cars in its fleet is working to prepare for the Papal visit by adding at least 15 more wheelchair accessible cabs. Because of regulations, it can’t spike fares (a la Uber and Lyft) during big events.

“As far as revenues, drivers are aware there will be road closures,” Friedman said. “But there will be such an influx of people, that there will be increased demand for any type of transportation, including taxi cabs.”

She also said the cab company expects to advertise heavily during the Pope visit as a legal transportation service “in a legitimate vehicle.”

That’s a shot at UberX, which has been (technically) operating illegally in Philadelphia since last fall. Uber cars have been impounded by the Philadelphia Parking Authority because the service isn’t allowed here in the city, but the network continues to have a heavy presence in Philly.

Jon Feldman, general manager for Uber in Philadelphia, said through a spokeswoman that the company has had conversations with World Meeting of Families officials to coordinate how the service can help transport some of the millions of people who will be in town.

“Being such a flexible platform, we’re able to better match supply and demand than Philly’s limited supply of taxis can,” he said. “And, our technology can provide information to driver-partners in real time on hot-spots in the city, and areas where safe, reliable rides are in high demand.”

Nutter said Tuesday that further information including road closures and security information will be released closer to the date of the event.

Anna Orso was a reporter/curator at Billy Penn from 2014 to 2017.