Madrid banned older cars from its city center.
In December, Madrid began restricting access to gas-powered vehicles made prior to 2000 and diesel vehicles made prior to 2006. Exceptions are currently being made for cars with a private parking spot that are registered in advance. Come 2020, older diesel and gas-powered cars won't be allowed to enter at all.
Older diesel and gas-powered taxis will have until 2022 before the ban goes into effect, 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 around $100.
On its first day, the ban successfully cut traffic on Madrid's busiest street by a third. The city expects the ban to impact around 20% of the cars entering its urban core.
In Paris, the first Sunday of every month is free of cars.
A 2018 study found that Paris has the second worst air quality among 13 European cities, behind Moscow, but ahead of London.
The city's major, Anne Hidalgo, has made it a personal mission to improve pollution levels by imposing numerous restrictions on vehicles. Cars made before 1997 have been banned from the city center on weekdays, and the city plans to limit select streets to electric cars by 2020.
Hidalgo recently declared the first Sunday of every month car-free from 10 a.m. to 6 p.m. in the urban core — a rule that's already been established in other parts of the city.
New York City banned cars from Central Park.
New York City's car-free initiatives may lag behind those in European cities, but they're still far ahead of the curve in the US.
In addition to creating permanent, pedestrian-only zones in popular areas like Times Square, Herald Square, and Madison Square Park, the city has banned cars from the internal streets of Central Park, which receives around 42 million visitors each year.
"This park was not built for automobiles," Mayor Bill de Blasio said while announcing the plan in April. "It was built for people."
The city also built more protected bike lanes in 2018, though there's some controversy over whether it exaggerated the scope of its efforts.
Oslo's city center is on its way to becoming car-free — but not all politicians are pleased.
The Norwegian capital is on a mission to become carbon neutral by 2030, and restricting vehicles is a key part of its goal.
2019 ushered in a series of car-free measures in Oslo's city center, including restricted access for private vehicles, new pedestrian walkways, and 700 fewer parking spots.
The city originally planned to permanently ban all cars from the urban core — an initiative that one conservative party politician called "a Berlin wall against motorists."
While the plan is slightly behind schedule, Oslo's vice mayor for urban development has maintained that the city center will be free of private vehicles by 2020.
London could ban cars on half the streets in its city center.
In October, at least half the roads in London's city center were dubbed "pedestrian priority" zones. The city hopes to deny access to cars, vans, taxis, and buses in these areas.
The new measures are part of an ambitious plan to reduce traffic in the Square Mile — London's urban core — which sees around 480,000 daily commuters.
Starting in April 2019, private vehicles, including Uber and minicabs, will be added to the list of cars that must pay a $14.70 daily "congestion fee" for driving in central London.
The number of daily vehicles entering central London declined by 30% since the fee was instated in 2003, the city's government transportation agency told the BBC.
Mexico City prohibited driving on Saturdays, but it didn't go as planned.
Mexico City was once the world's most polluted city, but has since improved its air quality thanks to a policy that prevented drivers from using their cars once per week.
In 2008, the city tightened these restrictions by prohibiting cars from driving on Saturdays as well. The plan hoped to reduce vehicle emissions by 15%, but a follow-up study by a US researcher found that air pollutants hadn't changed much as of 2017.
The researcher found that people opted for a taxi or to carpool with a family member on the day they weren't allowed to drive.
"Driving is a real status symbol in Mexico City," the researcher, Lucas David, told the BBC. "There's a bit of a cultural or socio-economic resistance to taking public transport."
Copenhagen's bike-friendly atmosphere discourages driving.
Copenhagen could soon benefit from a nationwide policy in Denmark that would ban the sale of new petrol and diesel cars starting in 2030, and the sale of hybrid cars starting in 2035.
The city is also extremely bike-friendly, with more than half of its population choosing to bike to work each day. These commuting habits are encouraged by a series of bicycle-only superhighways, along with pedestrian-only zones that have been around since the 1960s.
The city now has one of the lowest rates of car ownership in Europe.
Brussels is using cameras to enforce a fine for old vehicles.
Brussels recently imposed a $400 fine on diesel vehicles that enter the low-emission zone of its city center. The restrictions are enforced via hundreds of security cameras along the border, but environmentalists say they only apply to about 1% of the city's cars.
The city ultimately hopes to ban all diesel vehicles by 2030.
Brussels has also enacted a number of measures to promote alternate forms of transportation. A new emergency plan stipulates that subway, trams, buses, and shared bikes will become free to the public on high-air-pollution days.
Milan is rolling out a series of bans.
Starting on January 21, the city will prohibit older diesel vehicles from driving on weekdays. From there, it'll extend the ban to other diesel cars.
In September, the city also joined Rome in implementing a three-day ban on private car use.
Rome could help preserve its monuments by banning diesel cars.
The air quality in Rome is so bad, it's threatening the longevity of the city's monuments. A 2017 study from the city's culture ministry found that 3,600 stone monuments and 60 bronze sculptures might seriously deteriorate due to air pollution.
To combat this risk, Rome has pledged to ban diesel vehicles from the city center by 2024. The city has also attempted to instate a number of temporary bans, which some residents have found a way to skirt.
Athens joined a pledge to ban diesel cars by 2025.
In December 2016, Athens Mayor Giorgos Kaminis joined the mayors of Paris, Madrid, and Mexico City in a pledge to ban diesel vehicles by 2025. At the time, Kaminis said he hoped to eventually ban all cars from the urban core.
That's still far from the case, though the city does restrict diesel vehicles from entering the city center on certain days. License plates that end in an even number are restricted from driving on even dates, and plates that end in an odd number are restricted from driving on odd dates.
A court ordered Frankfurt to ban around 60,000 cars.
In September 2018, a federal court ordered Germany's financial capital to ban all but the newest versions of diesel vehicles — about 60,000 cars in total — by the following year.
German Chancellor Angela Merkel has opposed the measure, calling it "disproportionate." A representative for Germany's largest motor organization also accused the ban of placing undue financial strain on car owners.
Germany is one of six countries that were recently taken to court by the European Union for exposing their citizens to too much air pollution.
Berlin received a similar court order.
A month after the court ruling in Frankfurt, Berlin was also ordered to ban diesel cars manufactured prior to mid-2015 in certain parts of the city. The ban is set to go into effect in April, at which point around 200,000 cars will be affected.
The German government has also offered incentives to customers who retrofit their older cars to make them more fuel-efficient.
Bogotá closes its streets every Sunday from 7 a.m. to 2 p.m.
Bogotá, Colombia, has been running a car-free program called Ciclovía since 1974. Every Sunday, the program shuts down more than 75 miles of roads to cars and attracts around 1.7 million pedestrians — about a quarter of the city's population.
The city also runs a program called Pico y Placa (Peak and Plate), which restricts odd and even license plates on alternating days.
Amsterdam wants to only allow emissions-free vehicles by 2030.
The Dutch government has put forward a plan to only allow emissions-free vehicles by 2030.
In the meantime, they've set aside around $115 million to improve bike paths and parking, and around $282 to improve bicycle infrastructure.
Although cycling is already quite popular in Amsterdam, the Netherlands' state infrastructure secretary hopes to add another 200,000 cyclists to its roads.