Provincial highways in Ontario

The Ontario provincial highway network consists of all public highways maintained by the Canadian province of Ontario. The Ministry of Transportation of Ontario (MTO) maintains over 16,600 kilometres (10,300 mi) of roadways organized into various classifications which crisscross the province and provide access to major population centres.

Like most provinces, Ontario established a highway network in early 1920 as a result of the Canada Highways Act. Initially, the responsibility for these roads fell under the Department of Public Highways. In 1930, the department was renamed as the Department of Highways (DHO). Roadways in sparsely populated northern Ontario fell under the Department of Northern Development (DND) until it was merged into the DHO in 1937. That same year, the first divided highway and interchange in Canada – The Middle Road – was opened, inspired by German autobahns. Following World War II, construction of highways was accelerated; the first fully controlled-access highway was opened between Toronto and Barrie in 1952, the 825 km (513 mi) Highway 401 was navigable in 1964, and a network of secondary and collector highways was constructed through the rugged Canadian Shield throughout the 1950s. In 1960, The Gap opened along the north shore of Lake Superior and completed the Trans-Canada Highway in the province. The decade that followed saw the opening or planning of almost every freeway in Southern Ontario completed to date. In recent years, work has been focused on twinning existing routes into divided highways rather than establishing new corridors.

Ontario has several distinct classes of highways: King's Highways, (which includes Controlled-access highways) and secondary highways, with individual highways referred to as "that part of the King's Highway known as No. xx," or simply "the King's Highway known as No. xx." For the purposes of legal jurisdiction, however, the Highway Traffic Act deems that tertiary roads are also considered to be "King's Highways".

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