Madrid's ban on cars cut traffic on its busiest street by a third - and other cities are cracking down

• Madrid recently enacted a ban on older cars, which prohibits them from entering the city center without a private parking spot and advanced registration.
• By 2020, older diesel and petrol cars won't be allowed to enter the city center at all.
• The new regulations represent a larger trend of restricting vehicles to reduce traffic and air pollution.

Recent years have ushered in a "war on cars" in cities.

As urban areas become more crowded and roads become more congested, city governments have taken up arms against excess traffic and parked vehicles.

Cars are also frequent contributors to air pollution, one of the main causes of worldwide deaths, behind smoking, high blood pressure, and diet. In addition to releasing harmful substances like carbon monoxide, cars produce greenhouse gas emissions that are damaging to the environment.

Read more: 13 cities that are starting to ban cars

The city of Madrid heeded this warning last week with a ban on older cars, which are now prohibited from entering the city center.

The ban is part of a municipal-led initiative called Madrid Central, which aims to reduce levels of nitrogen dioxide, a harmful pollutant that can cause lung irritation and lead to respiratory infections like pneumonia.

The ban restricts the access of petrol vehicles made prior to 2000 and diesel vehicles made prior to 2006, which are only permitted if they have a private parking spot and are registered in advance. Come 2020, these cars won't be allowed to enter at all.

Older diesel and petrol taxis are permitted until 2022, while hybrid vehicles with an "eco label" are granted free reign.

Any car that's found in violation of the new rules will have to pay a fine of about $100. The city expects the ban to impact around 20% of the cars entering the urban core.

Their estimates proved somewhat accurate on the first day of the ban, which reduced traffic on the city's busiest street, Gran Vía, by nearly a third, according to the Spanish newspaper El País. Other streets saw reductions ranging from 6% to 14%.

Madrid joins a host of cities that are cracking down on older vehicles, which produce substantially more emissions than new cars. Already, the city of Paris has instated car-free Sundays in the urban core, as well as an annual car-free day throughout the entire city. Cities like London and Athens have proposed similar bans on diesel or petrol vehicles.

Many citizens and politicians have criticized these bans as unfairly targeting low-income residents, who are more likely to drive older cars. Others see it as a necessary measure to prevent tens of thousands of premature deaths.

"We've reached a point where it's healthier for some people to stay inside and not exercise, rather than walk outside and breathe polluted air," wrote Audrey de Nazelle, a senior lecturer in air pollution management at Imperial College London, in a recent blog post.