King's Highway 401, commonly referred to as Highway 401 and also known by its official name as the Macdonald–Cartier Freeway or colloquially referred to as the four-oh-one,is a controlled-access 400-series highway in the Canadian province of Ontario. It stretches 828 kilometres (514 mi) from Windsor in the west to the Ontario–Quebec border in the east. The part of Highway 401 that passes through Toronto is North America's busiest highway, and one of the widest.Together with Quebec Autoroute 20, it forms the road transportation backbone of the Quebec City–Windsor Corridor, along which over half of Canada's population resides. It is also a Core Route in the National Highway System of Canada.The route is maintained by the Ministry of Transportation of Ontario (MTO) and patrolled by the Ontari