page_title: Ontario Highway 401
section_title: Greater Toronto Area
hierarchical_section_title: Ontario Highway 401 / Route description / Greater Toronto Area
caption_attribution_description: A CCTV camera on the southeast corner of the Warden Avenue overpass of Highway 401. The cameras are mounted on high poles all along the highway, and are used along with vehicle detectors in the pavement to provide traffic information on changeable message signs along the highway.
context_page_description: 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 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 and patrolled by the Ontario Provincial Police. The speed limit is 100 km/h throughout its length, with the only exceptions the posted 80 km/h limit westbound in Windsor and in most construction zones.
context_section_description: As Highway 401 approaches the Greater Toronto Area (GTA), it descends through the ecologically protected Niagara Escarpment to the west of Milton.
  Upon entering the town, it enters the first urbanized section of the GTA, passing through two rural areas between there and Oshawa. The first rural gap is the western side of Toronto's Greenbelt, a zone around Toronto protected from development. After this 10 km (6.2 mi) gap, the highway interchanges with the Highway 407 Express Toll Route. Within the GTA, the highway passes several major shopping malls including Yorkdale Shopping Centre, Scarborough Town Centre and Pickering Town Centre.
  Highway 401 widens into a collector-express system
  as it approaches Hurontario Street in Mississauga, a concept inspired by the Dan Ryan Expressway in Chicago. The system divides each direction of travel into collector and express lanes,
  giving the highway a wide span and four carriageways. To avoid confusion between carriageways, blue signs are used for the collector lanes and green signs for the express lanes. Unlike the collector lanes, which provide access to every interchange, the express lanes only provide direct access to a select few interchanges. Access between the two is provided by transfers, which are strategically placed to prevent disruptions caused by closely spaced interchanges.
  The overall purpose of the collector-express system is to maximize traffic flow for both local and long-distance traffic. In addition, Highway 401 was equipped with a traffic camera system called COMPASS in early 1991.
  Using closed-circuit television cameras, vehicle detection loops and LED changeable-message signs, COMPASS enables the MTO Traffic Operations Centre to obtain a real-time assessment of traffic conditions and alert drivers of collisions, congestion and construction.
  The system stretches from the Highway 403 / 410 interchange in Mississauga to Harwood Avenue in Ajax.
  Two sets of collector-express systems exist in the GTA. The first set is 6.6 km (4.1 mi) long and connects Highway 403, Highway 410 and Highway 427.
  This system primarily serves to accommodate and organize various traffic movements from the Highway 403 / 410 and Highway 427 interchanges along Highway 401, replacing an earlier plan that would have run Highway 403 directly to Eglinton Avenue and the never-built Richview Expressway. East of the interchange with Renforth Drive, the collector lanes diverge to become the on-ramps to Highway 427 northbound and southbound. The second 43.7 km (27.2 mi) system passes through the centre of Toronto and ends in Pickering to the east.
  The 5 km (3.1 mi) gap between the two systems is a traffic bottleneck. However, the interchange cannot accommodate future widening of Highway 401.
  Highway 401 widens to 18 lanes south of Toronto Pearson International Airport. Progressing eastward, eight lanes are carried beneath the large spaghetti junction at Highway 427. The highway curves northeast and follows a power transmission corridor to Highway 409, which merges with the mainline and forms the collector lanes. It returns to its eastward route through Toronto, now carrying 12–16 lanes of traffic on four carriageways.
  Highway 401 is often congested in this section, with an average of 442,900 vehicles passing between Weston Road and Highway 400 per day as of 2008. In spite of this congestion, it is the primary commuting route in Toronto; over 50 percent of vehicles bound for downtown Toronto use the highway.
  East of Highway 400 is The Basketweave, a criss-crossing transfer between the express and collectors carriageways, beyond which is Yorkdale Centre. Twelve lanes pass beneath a complicated interchange with Allen Road, built to serve the cancelled Spadina Expressway. Further east, the highway crosses Hogg's Hollow, over the West Don River and Yonge Street in the centre of Toronto, the busiest multi-span bridge crossing in North America, surpassing the Brooklyn Bridge. It then crosses the East Don River and climbs toward the Don Valley Parkway, which provides access to downtown Toronto and Highway 404, 
caption: Traffic cameras are mounted at every exit within Toronto and form one part of the COMPASS system.
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