Paris has significantly reduced traffic since 1990 but this was not an easy or quick task. This article suggests sustained effort from the city’s mayors was critical:

• Jacques Chirac, Paris’ famously conservative (and public fund-embezzling) mayor from 1977 to 1995, helped encourage pedestrianism by increasing the number of bollards to prevent illegal sidewalk parking, Héran writes. Chirac also rehabilitated the Champs-Elysees into a true public promenade, with widened sidewalks, street parking eliminations, and refreshed green spaces.
• Chirac’s chosen successor, Jean Tibéri, came under fire for not cracking down hard enough on Paris’ air quality problems (and was accused of election fraud!), but he does get credit for banning cars in the Place de la Concorde. In an effort to reduce traffic, he also introduced the city’s first bike plan in 1996, which established paths along the city’s main arteries and lower-speed neighborhood zones, Héran notes.
• Elected Paris’ first openly gay mayor in 2001, the socialist Bertrand Delanoë “vowed that automobile interests would no longer dominate the city and he would focus on improving public spaces,” wrote Stephane Kirkland for the Project for Public Spaces in 2014. Delanoë made good on those promises during his 13-year tenure (while largely avoiding scandal): A number of streets were reconfigured to accommodate dedicated bus lanes. Some 400 miles of bicycle lanes were created. The banks of the Seine began to close to traffic in the summertime to make way for public “beaches.”And in 2007, the city introduced its bikeshare program, Vélib, now arguably the largest and most used such system in the West.
• Delanoë’s protégé and current Mayor Anne Hidalgo is an outspoken environmentalist responsible for “some of the most systematically anti-car policies of any major world city,” CityLab’s Feargus O’Sullivan wrote last year. Hidalgo has implemented a ban on older cars on roads during weekdays, and has pedestrianized the lower quays of the Seine. “Car space is being slashed in many major squares, while car-free days have been introduced annually as a form of publicity campaign for a future without automobiles,” O’Sullivan wrote. (Furthermore, recent trip data from city hall do not support the claim by some motorists that Mayor Hidalgo’s car-free policies have made congestion worse. There’s been a sharp decline in the kilometers-traveled within the city, but only a small dip in kilometers-per-hour.)
• Paris’ commitment to public transport far surpasses that of any city in the U.S., where it has been more than 30 decades since any new system opened. RATP, the public transport operator for the Île-de-France region, has increased its reach with new bus rapid-transit lines and a steadily growing suburban tram network whose first line opened in the early 1990s. New routes have been accompanied by sidewalk improvements, bike paths, and a variety of traffic calming measures. The lines are frequent and fast. Some are even driven autonomously.

Three quick thoughts regarding this brief history of Paris:

1. Sustained effort across mayors and local government officials is not easy to do. This article covers 25+ years where different actors from different perspectives contributed to a desirable outcome. The amount of emphasis on reducing traffic probably differed quite a bit across administrations yet the small and big steps added up over time. Significant social change in large cities does not often happen quickly.
2. The reasons for pursuing less car traffic are varied. Some might decry the environmental issues. Others might want more space for bicycling. More public space might motivate others. I wonder if any of these one reasons would have been enough to motivate these actions and push forward big changes. But, put together multiple reasons and people with different interests might be more likely to come together and promote fewer cars.
3. How much easier is it to pursue such plans in a European city versus an American city? Additionally, this is Paris, a tourist hot-spot where people want to walk around and experience charming sights and neighborhoods. American cities may also desire less traffic – who wants to be delayed? – yet this is difficult to reconcile with American desires for individual transportation. At the same time, a chart in the article suggests London and Berlin are more like New York City in terms of driving.