Ontario Highway 401

The Macdonald-Cartier Freeway, more commonly known as Highway 401, is a highway that runs across southern Ontario, Canada, the longest of the 400-series of highways in Ontario.

It begins at Highway 3 in Windsor, Ontario (not at the Michigan border), and ends at the border with Quebec, 815 kilometres to the east. Construction began in 1939, but was almost immediately shut down due to the outbreak of World War II. The first section of the highway was opened between Toronto and Oshawa in 1947, and it was officially designated 401 in 1952. The section of the highway that ran through Toronto quickly became an urban commuter road, rather than a long-distance bypass route as was originally planned, leading to extensive traffic jams. This problem was solved to some extent by creating an express route along with a local route along the Toronto section. By 1967 the highway had been expanded from two lanes in each direction to six lanes, but due to the express/local design, some parts became nine lanes wide in each direction.

In 1965 Premier John Robarts named the highway the Macdonald-Cartier Freeway, in honour of Sir John A. Macdonald and Sir Georges-Etienne Cartier, two of the most important Fathers of Canadian Confederation.

Today up to 400 000 vehicles use it every day, and there are 18 service stations located along the route. It is one of the most important highways in Canada, as it connects the majority of the population of southern Ontario with all the other highways in the province, as well as all the roads that cross the border with the United States. The border crossing at Windsor and Detroit is the busiest in Canada, and although the 401 itself does not extend the last few kilometres into Detroit, it is the only route from Toronto to Windsor. A large majority of trade between Canada and the United States is carried out due to the 401.

Notable cities along the route of the highway include Windsor, Chatham, London, Woodstock, Ontario, Kitchener, Cambridge, Mississauga, Toronto, Oshawa, Cobourg, Belleville, Kingston, and Cornwall.