Hidalgo acknowledged that the event was not as expansive as she had hoped, but she aims to extend it next year. "We didn't get as wide a perimeter as we'd have liked, we asked for the whole of Paris," she told reporters before officially opening the event. "But it's a first and I think next year it will be even bigger."

But the case study was far from comprehensive. The ban covered only four of Paris' 20 arrondissements, in addition to tourist attractions like the Champs Elysée, and environmental groups have criticized the city for not extending it to working-class neighborhoods. Others have claimed that the campaign would have been more effective had it been launched on a weekday, thereby forcing Parisians to re-think their daily commutes. Exceptions were made for public buses, ambulances, and taxis, while drivers outside of the no-car zone were asked to respect a speed limit of 12 miles per hour. (Many did not.)

The mayor has made environmental stewardship a priority since coming into office in 2014, and she has proposed ambitious initiatives to clean up the city. Following the lead of her predecessor, Bertrand Delanoë, Hidalgo has called for the creation of a pedestrian-only zone along the right bank, where a major highway currently runs, and has pushed to ban all diesel cars from Paris by 2020. She has also said she wants to see people swimming in the heavily polluted Seine river by 2024, in time for the Summer Olympic Games that Paris is currently bidding to host.

For a few hours on Sunday, Parisians and tourists in central Paris were able to get a taste of what car-free life would actually look like. A major thoroughfare along the Seine was dotted with joggers, bikers, and families pushing strollers under a cloudless sky. A few hundred meters inland, behind the Louvre, the usually bustling rue de Rivoli was strangely quiet, its engine roars and car horns replaced by the soft bell dings of attentive cyclists. Cabs and busses crawled by in dedicated lanes, but they moved at the whim of pedestrians.

The atmosphere was idyllic, festive, and at times, a little eerie. And, like many pleasant things, it was ultimately fleeting. By 6PM, the horns and the exhaust pipes had returned, and Paris moved forward.