A car-free day is a day when people do not drive cars. Some cities, towns and neighborhoods celebrate this day to help reduce the amount of carbon dioxide and other pollution in the air. It is also a way to encourage people to use public transportation, bicycles, or just walk instead of getting in a car. On a car-free day, all roads in the city or town are closed to cars, but buses, trucks and motorcycles are still allowed on the roads. People who usually drive cars just have to find another way to get around.