PHILADELPHIA EXPERIENCED SOMETHING STRANGE when the Pope came to town last year. A visit from the Pope, of course, means lots of crowds and heightened security. In order to accommodate the event, the city closed off the city center’s streets. And it was really, really cool. You could walk in the road. You could go biking. You could chat with your neighbors. All without having to worry about traffic.

Philadelphians liked the car-free Pope days so much that they campaigned to make it into a regular holiday. This year, on September 24th, Philadelphia is closing off nine miles of streets to cars, and leaving it open for pedestrians and cyclists. They’re planning an entire festival around it.

Philly Free Streets came about in a unique way, but it isn’t the first such festival. New York City runs an event called Summer Streets, which opens up seven miles of city streets to more sustainable forms of transportation. Last year, 300,000 people took part in the New York event.

Clarena Tolson, Philadelphia’s deputy manager for transportation and infrastructure, said she hopes that the festival will become a model for cities all over the country. “We think ultimately this is going to be the coolest, hippest event in the country,” she told website Billy Penn.

Aside from just generally being a fun way to give cities back to pedestrians, Philly Free Streets is addressing much bigger problems: public health and climate change. Walking is good for you. Not breathing exhaust fumes is also good for you. And more walkers and fewer cars is better for the atmosphere. But unfortunately, most US cities are built for cars. Worldwide, cities contribute upward of 70% of global emissions.

More and more people are moving to cities, and if those cities are car-heavy and unwalkable, it’s not going to mean great things for our health and climate. “If we want to not bring on climate change, then it’s amazing how key walking is to that,” walkability expert Dan Burden told Grist. He suggests a number of things to make cities more walkable, including turning city streets into more social places. And by making cities more walkable, we’re not only helping the environment, but we’re reducing obesity and mental illness.

So with any luck, Philly Free Streets catches on in other cities. If it doesn’t, we’re just going to have to ask the Pope to hit more cities on his US world tour next time.

h/t: Billy Penn.