Alternate-side parking is a traffic law that dictates on which side of a street cars can be parked on a given day. The law is intended to promote efficient flow of traffic, as well as to allow street sweepers and snowplows to reach the curb without parked cars impeding their progress. Some proponents also regard the law, which can be quite inconvenient for drivers, as a way to encourage the use of public transportation. In many towns and cities, alternate-side parking is reserved for certain times of year, or only used during a snow emergency.