King's Highway 17, more commonly known as Highway 17, is a provincially maintained highway and the primary route of the Trans-Canada Highway through the Canadian province of Ontario. It begins at the Manitoba boundary 50 km (31 mi) west of Kenora and the main section ends where Highway 417 begins just west of Arnprior. A small disconnected signed section of the highway still remains within the Ottawa Region between County Road 29 and Grants Side Rd. This makes it Ontario's longest highway.[note 1]
The highway once extended even farther to the Quebec boundary in East Hawkesbury with a peak length of about 2,180 km (1,350 mi). However, a section of Highway 17 "disappeared" when the Ottawa section of it was upgraded to the freeway Highway 417 in 1971. Highway 17 was not re-routed through Ottawa, nor did it share numbering with Highway 417 to rectify the discontinuity, even though Highway 417 formed a direct link between the western and eastern sections of Highway 17. However, from East Hawkesbury to Ottawa, Highway 17 retained the Trans-Canada Highway routing and signs until it met up again and merged with Highway 417 until 1997, when Highway 17 through Ottawa was downgraded. The Trans-Canada Highway designation now extends along all of Highway 417.
Ontario Highway 17 is a very important part of the national highway system in Canada, as it is the sole highway linking the eastern and western regions of the country. It is the only road that links the province of Ontario with the province of Manitoba, making it a major section of Canada's primary commercial and leisure route for all traffic travelling between Canada's largest cities, from Toronto and Montreal in the east to Calgary and Vancouver in the west.
With the establishment of the provincial highway network on February 26, 1920, the Department of Public Highways, predecessor to today's Ministry of Transportation of Ontario, sought to establish a network of reliable roads through the southern part of the province. Through July and August 1920, a highway east of Ottawa to Pointe-Fortune at the Quebec boundary, known as the Montreal Road, was assumed by the department. This original routing of Highway 17 followed what is now Montreal Road, St Joseph Boulevard, and the Old Montreal Road eastward out of Ottawa; Laurier Street through Rockland; Regional Road 55 and 26 between Clarence and Plantagenet; Blue Corner Road and Bay Road (Regional Road 4) to L'Original; John Street, Pharand Street, Eliza Street, Front Road and Main Street to Hawkesbury; the shore of the Ottawa River between Hawkesbury and Pointe-Fortune, and Regional Road 17 elsewhere. A portion of this original highway was lost when the completion of the Carillon Generating Station in 1964 raised the water level of the Ottawa River north of Voyageur Provincial Park.
West of Ottawa, a route was assumed to Arnprior on October 6, following today's Carling Avenue, March Road and Donald B. Munro Drive between Ottawa and Kinburn, and Mohrs Road, Galetta Sideroad and Madawaska Boulevard between Kinburn and Arnprior. On June 15, 1921, the highway was extended to Pembroke via Renfrew, Cobden and Beachburg. The entire route between Pembroke and Pointe-Fortune became known as Highway 17 in the summer of 1925.
Although the jurisdiction of the soon-to-become Department of Highways did not extend beyond Pembroke, a rough trail continued to North Bay, and a trunk road constructed by the Department of Northern Development beyond there to Sault Ste. Marie by 1923, roughly following the route of Highway 17 today. The Pembroke and Mattawan Road Colonization Road was constructed between 1853 and 1874 to encourage settlement in the Upper Ottawa Valley. Between Mattawa and North Bay, many aboriginals and early settlers made use of the Mattawa River, the headwaters of which lie just north of Lake Nipissing. From there they would travel down the French River into Georgian Bay and onwards to Lake Superior. Highway 17 between Mattawa and Sault Ste. Marie roughly traces this early voyageur route.
Following World War I, discussions of a cross-continental road through Canada became vocal and construction of such a route was underway in several places. However, funding for this work was soon halted as the government distributed funding to projects that were believed to be more important than the luxury of the new road. The most significant accomplishment of this work was the Nipigon Highway between Thunder Bay and Nipigon, opened in 1924.