Calle de Alcalá in Madrid, Spain. Wikipedia Commons

In late 2016, Madrid's Mayor Manuela Carmena reiterated her plan to kick personal cars out of the city center.

On Spanish radio network Cadena Ser, she confirmed that Madrid's main avenue, the Gran Vía, will only allow access to bikes, buses, and taxis before she leaves office in May 2019. It's part of a larger effort to ban all diesel cars in Madrid by 2025.

But the Spanish city is not the only one getting ready to take the car-free plunge. Urban planners and policy makers around the world have started to brainstorm ways that cities can create more space for pedestrians and lower CO2 emissions from diesel.

Here are 12 cities leading the car-free movement.