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 Ontario Provincial Police. The speed limit is 100 km/h (62 mph) throughout its length, with the only exceptions being the posted 80 km/h (50 mph) limit westbound in Windsor and in most construction zones, along with a 110 km/h (68 mph) speed limit between Windsor and Tilbury.
Highway 401 looking west at split with Highway 402 in London.
Highway 401 eastbound express lanes at Weston Road. This section has a volume of over 500,000 vehicles per day during the summer months.
Different colours are used on the signs on Highway 401's collector-express system to avoid confusion. The express lanes use green signs and the collector lanes use blue.
"The Basketweave", just east of the Highway 400 interchange, is a free-flowing crossover between the collector and express lanes.
Controlled-access highway
A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway, and expressway. Other similar terms include throughway or thruway and parkway. Some of these may be limited-access highways, although this term can also refer to a class of highways with somewhat less isolation from other traffic.
The cloverleaf interchange between US 131, M-6 and 68th Street in Cutlerville, Michigan, United States, shows many of the features of controlled-access highways: entry and exit ramps, median strips for opposing traffic, no at-grade intersections and no direct access to properties.
Typical overhead signage on Ontario's King's Highway network featuring an airport pictogram, distances to upcoming interchanges, and lane guidance
An aerial view of Finnish national road 3 (E12), a motorway between Tampere and Helsinki in Finland
Autostrada A1 (E35/E45) runs through Italy linking some of the largest cities of the country: Milan, Bologna, Florence, Rome and Naples