What Paris learned from closing a road.

For years, traffic moved along the Seine where people now walk beside the water. Paris began transforming the left-bank expressway into a pedestrian promenade in 2013. The right-bank expressway followed in 2016, during Mayor Anne Hidalgo’s tenure. The changes were contentious, and predictions of gridlock were familiar: remove a road and surely every car will go somewhere else, all at once.

I am Ines Halvorsen, a former transit planner. The useful lesson is not that closing a road has no consequences. It is that traffic patterns respond. Some drivers change routes, departure times, destinations, or modes; some trips may not happen. Researchers call this “traffic evaporation,” the observed possibility that traffic can diminish when road capacity is reduced, rather than simply reappearing elsewhere in full.

A public space, not an empty road.

The riverbanks became places for walking, cycling, and spending time near the water. That change made the decision tangible: the city was reallocating space from through-traffic to public use. The argument was never only about vehicle speed. It was about what kind of access the center of Paris should provide and who should benefit from the riverfront.

A road is not the absence of a choice. It is a choice about what the street is for.

The closures also faced legal challenges. Courts and public authorities considered the decisions and their effects, illustrating that a major street change has to survive more than a traffic forecast. The process involves law, environmental review, public debate, and the practical question of how neighboring streets and transit will work.

“Traffic evaporation” should not be used as a promise that every closure will make congestion disappear. Effects depend on the street network, travel alternatives, land use, and how the change is implemented. A city should measure what happens on adjacent routes, support transit and walking, and explain how access for deliveries, residents, and emergency services will be handled.

Other cities can take a method from Paris, not a template: identify what public purpose a road serves, test how the space could serve more people, and monitor the network after the change. Make the alternative legible and useful. Then judge the project by the streets and lives it creates, not only by whether every former car trip found another road.

— Ines