Bryan McAllister’s personal reference notebook
July 27, 2026Short & citedBlog
Civic Viewpoint.
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Kept by Bryan McAllister — short guides, clear facts, and the Canadian angle when it matters.
Civic Brief • Canada Notes

Highway 401

Highway 401 is a 400-series freeway in Ontario, Canada, officially known as King’s Highway 401 and the Macdonald–Cartier Freeway.

Updated July 27, 20261 min readCited sources

Highway 401 is a major 400-series freeway in Ontario, Canada. It is the busiest highway in Canada, running from Windsor to the Quebec border.

What it is

Highway 401, officially King’s Highway 401 and the Macdonald–Cartier Freeway, is an 828-kilometre (514-mile) east–west freeway across southern Ontario. It connects Windsor, London, the Greater Toronto Area, Kingston, and the Ontario–Quebec border, making it Ontario’s longest provincial highway.

Why it matters

The highway is a critical corridor for commuters and freight, with the Toronto section among the busiest road segments in North America. It forms part of the Quebec City–Windsor Corridor and Canada’s National Highway System, supporting economic activity in one of the country’s most populated regions.

Key details

Construction began in the 1940s, with the first sections opened in 1947 and the route completed by 1968. The highway has been expanded and upgraded in selected areas over time. It is a core route for long-distance travel and trade across southern Ontario.

In short

  • Highway 401 is the longest 400-series highway in Ontario at 828 km.
  • It links Windsor, Toronto, Kingston, and the Quebec border.
  • The Toronto section is one of the busiest highway segments in North America.
  • It is a major route for commuting and commercial transport.
Canadian angle

Highway 401 is one of Canada’s most important transportation corridors, carrying commuter and freight traffic through Ontario’s most populous region and linking major economic centres between Windsor and the Quebec border.

Quick questions

How long is Highway 401?
Highway 401 is about 828 kilometres long, or 514 miles.
What is the busiest highway in Canada?
Highway 401 is commonly described as the busiest highway in Canada, and its Toronto segment is among the busiest road sections in North America.
Where does Highway 401 run?
Highway 401 runs from Windsor across southern Ontario to the Ontario–Quebec border, passing major centres such as London, Kitchener–Waterloo, Toronto, Oshawa, Kingston, and Cornwall.

Sources

  1. Wikipedia — https://en.wikipedia.org/wiki/Ontario_Highway_401
    Supports: Length, termini, official and alternate names, traffic significance, core route status, history overview
  2. Simple English Wikipedia — https://simple.wikipedia.org/wiki/Ontario_Highway_401
    Supports: Length, route endpoints, general description
  3. Ontario Highways — https://www.asphaltplanet.ca/ON/highway_401.htm
    Supports: Length estimate, exits count, traffic importance, Toronto segment congestion
  4. Wikipedia (French) — https://fr.wikipedia.org/wiki/Autoroute_401_(Ontario)
    Supports: Length, route, construction timeline, commercial importance