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Thousands of pilgrims are streaming toward the Benjamin Franklin Parkway, site of this afternoon’s papal Mass. Scores more, hundreds deep, are already waiting to get to the parkway at security checkpoints. The mood is happy, the crowds orderly and in good spirits.

They are filling downtown streets that are normally the domain of cars and roaring buses. But inside what is known as the papal “traffic box” — the central districts of Philadelphia, where incoming cars have been banned for the weekend — the traffic is almost entirely on foot or two wheels. Bicyclists are out in large numbers.

The city’s bike community saw opportunities for freedom of movement and association that are rarely, if ever, available. For one: staging a dessert-themed Popesicle Bike Race down the middle of Pine Street.

Kristen Suzda and Travis Southard, the race’s organizers, met on Twitter and “decided to take advantage of all this,” Ms. Suzda said. “We’re celebrating our open streets.”

Two of the city’s leading ice-cream vendors sent employees to race cargo bikes, the chunky three-wheeled trikes used to make eco-friendly deliveries. (More were invited, but other ice-cream shops were either closed for the weekend, to escape the potential chaos of an expected million pilgrims, or they could not spare staff on what they were hoping to be a very busy sales day.)

The event got off to a shaky start when the cargo bike piloted by Lindsay Smith toppled, with her on it, perhaps because cargo bikes are not designed for racing. Unhurt save for a scrape or two, she and a fellow racer, James Fulwiler, returned to the start line and re-rode the one-block course, with Mr. Fulwiler the winner. “I just wanted to finish,” Ms. Smith said with a laugh. “I decided to take it slow.”

Saturday, hundreds of cyclists took to quiet, car-free streets for the Pope Ride, a miles-long course that threaded through Center City.

Bikers and pedestrians wanting a bit of open pavement to themselves have until early Monday morning. That’s when autos and buses start to return.