Ontario Highway 401
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 400-series highway in the Canadian province of Ontario. It is an freeway, travelling 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 in Canada. Together with 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 Canada's National Highway System. The route is maintained by the Ministry of Transportation of Ontario and patrolled by the Ontario Provincial Police. The speed limit is throughout the majority of its length, with the remaining exceptions being the posted limit westbound in Windsor, in most construction zones, and the speed limit on the stretch between Windsor and Tilbury that was raised on April 22, 2022, the extension east of the aforementioned, the stretch between Highway 35 / 115 and Cobourg, the stretch between Colborne and Belleville, the stretch between Belleville and Kingston, and the stretch between Highway 16 and the east end of the freeway that were raised on July 12, 2024.
By the end of 1952, three individual highways were numbered Highway 401: the partially completed Toronto Bypass between Weston Road and Highway 11 ; Highway 2A between West Hill and Newcastle; and the Scenic Highway between Gananoque and Brockville, now known as the "Thousand Islands Parkway". These three sections of highway were, respectively. In 1964, the route became fully navigable from Windsor to the Ontario–Quebec border. In January 1965, it was given a second designation, the Macdonald–Cartier Freeway, in honour of two Fathers of Confederation. At the end of 1968, the Gananoque–Brockville section was bypassed and the final intersection grade-separated near Kingston, making Highway 401 a freeway for its entire length. In August 2007, a portion of Highway 401 between Trenton and Toronto has been designated as the Highway of Heroes, as the route is travelled by funeral convoys for fallen Canadian Forces personnel from CFB Trenton to the coroner's office in Toronto.
Highway 401 previously ended at Highway 3 upon entering Windsor. In 2011, construction began on a westward extension called the Rt. Hon. Herb Gray Parkway. This extension runs parallel to Highway 3 between the former end of the freeway and the E. C. Row Expressway, at which point the extension turns and runs alongside the E.C. Row towards the future Gordie Howe International Bridge. An section of the parkway, east of the E. C. Row interchange, opened to traffic on June 28, 2015, with the remaining section completed and opened on November 21. The widening of the highway between Highway/Regional Road 8 in Kitchener and Townline Road in Cambridge to at least ten lanes was completed on December 22, 2023. There are plans underway to widen the remaining four-lane sections between Windsor and London to six lanes and to widen the route between Cambridge and Milton as well as through Ajax, Whitby, and Oshawa. The expansive twelve-plus-lane collector–express system through Pickering and Toronto, and partially across Mississauga, was extended west to Milton in December 2022.
Route description
Highway 401 extends across Southwestern, Central, and Eastern Ontario. In anticipation of the future expansion of the highway, the transportation ministry purchased a right-of-way along the entire length. Generally, the highway occupies only a portion of this allotment.It is one of the world's busiest highways; a 2019 analysis stated the annual average daily traffic count between Renforth Drive and Highway 427 in Toronto was at 450,300,
while a second study estimates that over 500,000 vehicles travel that section on some days. This makes it North America's busiest freeway, surpassing the Santa Monica Freeway in Los Angeles and I-75 in Atlanta. The just-in-time auto parts delivery systems of the highly integrated automotive industry of Michigan and Ontario have contributed to the highway's status as the world's busiest truck route, carrying 60 percent of vehicular trade between Canada and the US.
Highway 401 also features North America's busiest multi-structure bridge at Hogg's Hollow in Toronto.
The four bridges, two for each direction with the collector and express lanes, carried an average of 360,300 vehicles daily in 2019.
The highway is one of the major backbones of a network in the Great Lakes region, connecting the populous Quebec City–Windsor corridor with Michigan, New York and central Ontario's cottage country.
It is the principal connection between Toronto and Montreal, becoming A-20 at the Ontario–Quebec border.
Southwestern Ontario
Highway 401 does not yet extend across the Detroit River into Detroit, Michigan. However, by early 2026, the Gordie Howe International Bridge will extend Highway 401 across the Canada–United States border to a connection through Delray to I-75. At present, Highway 401 begins as a six-lane freeway in Brighton Beach at the west end of the E. C. Row Expressway, sandwiched between the E. C. Row's opposing carriageways for a short distance. Highway 401 then changes to a southeast direction as it descends into a trench and runs alongside Highway 3. This below-grade section of the highway has 11 tunnels to cross underneath surface streets. After passing under Howard Avenue and the ramps to Talbot Road, the highway then curves northeast and ascends back to the surface. At the split with Dougall Parkway, which links to the Detroit–Windsor tunnel, the highway turns east and exits Windsor. From here, Highway 401 mostly parallels the former route of Highway 98 from Windsor to Tilbury.File:Highway 401-Highway 402 interchange.jpg|right|thumb|Highway 401 looking west at split with Highway 402 in London.
Southwestern Ontario is flat, primarily an agricultural land, that takes advantage of the fertile clay soil deposited throughout the region.
The main river through the region is the Thames River, which drains the second-largest watershed in southern Ontario and largely influences the land use surrounding the highway.
The highway's route parallels the river to the south between Tilbury and Woodstock.
Near Tilbury, Highway 401 loses its tall wall median barrier, then narrows to four lanes, following lot lines laid between concession roads in a plan designed to limit damage to the sensitive agricultural lands through which the highway runs.
Here, the highway's flat, straight route is notorious for leading to driver inattention.
The section from Windsor to London has become known for deadly car accidents and pile-ups, earning it the nickname Carnage Alley.
As the highway approaches London, Highway 402 merges in, resulting in a six-lane cross-section.
Within London, it intersects the city's two municipal expressways, known as Highbury Avenue and the Veterans Memorial Parkway.
The section between London and Woodstock generally parallels the former Highway 2 but lies on the south side of the Thames River. This area is not as flat, but the freeway is generally straight. This part of Highway 401 often experiences heavy snowsqualls in early winter, sometimes extending as far east as Toronto. To the south of Woodstock, Highway 401 curves northeast as Highway 403 splits off at its western terminus. The freeway then meets the former Highway 2 at an interchange, reconfigured from a cloverleaf to a five-ramp parclo in the late 2000s, near the Toyota West Plant. From here, the highway heads towards Kitchener and Cambridge, substantially north of the route of the former Highway 2, which has been bypassed by Highway 403's western leg.
Heading towards Kitchener, the highway ascends as it crosses the Grand River, followed by interchanges with King Street and Highway 8 before returning to its eastward orientation. Between Highway/Regional Road 8 and Highway/Regional Road 24 in Cambridge, the highway was widened in 2020 to twelve lanes to accommodate the growing traffic using that segment.
Beyond Highway/Regional Road 24, the highway returns to a six-lane cross section, and meanders towards Milton, passing through hills and rock cuts along the way. As it enters Milton, it also enters Halton Region, part of the Greater Toronto Area.
Greater Toronto Area
As Highway 401 approaches the Greater Toronto Area from the west, it rounds Rattlesnake Point 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. Part of this rural gap is the western side of Toronto's Greenbelt, a zone around Toronto protected from development. After this gap, the highway interchanges with the Highway 407 Express Toll Route. Within the GTA, the highway passes several major shopping malls including Toronto Premium Outlets, Yorkdale Shopping Centre, Scarborough Town Centre, and Pickering Town Centre.
Within Greater Toronto, three separate segments of Highway 401 employ a collector-express system, a concept inspired by the Dan Ryan Expressway in Chicago. The system divides each direction of travel into segregated collector and express lanes,
giving the highway a wide span and four carriageways. 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. To avoid confusion between carriageways, blue signs are used for the collector lanes and green signs for the express lanes. The overall purpose of the collector-express system is to maximize traffic flow for both local and long-distance traffic.
From the west, the first collector-express section through the Greater Toronto Area is long, and runs from James Snow Parkway to Highway 407.
The highway briefly narrows to 10 lanes between the interchanges with Highway 407 and Winston Churchill Boulevard, then the second collector-express system begins and runs to Highway 427. The west end of this section initially terminated just west of Highway 410 in the early 1990s. It was extended westward in stages during the 2010s to include the interchanges with Hurontario Street, Mavis Road, and Mississauga Road ; with the final extension to Winston Churchill Boulevard being completed in 2022. Because Highway 403's eastern terminus feeds into the easternmost segment of the freeway's second collector-express section, this results in the Highway reaching its widest point, at 18 lanes. Running south of Toronto Pearson International Airport, the close proximity to the runways necessitates conventional light poles instead of high-mast lighting. Approaching the City of Toronto's western border, a final transfer allows eastbound traffic in the collector lanes to transfer to Highway 401 express lanes which continue under Highway 427 as the single eastbound Highway 401 carriageway. The Highway 401 collector lanes then become ramps to Highway 427 after a final exit at Renforth Drive and crossing into Toronto. For westbound traffic, the Highway's single westbound carriageway becomes the Highway 401 express lanes. The exit ramps from Highway 427 merge to form the start of the westbound Highway 401 collector lanes in this section. The collector lanes were originally designed to accommodate and organize various traffic movements from the Highway 403 / Highway 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 spaghetti interchange with Highway 427, the single carriageway of Highway 401 curves northeast and follows a hydro corridor to the east end of Highway 409. The space constraints of the existing flyovers at the 401/427 interchange also limit the width of Highway 401 through this junction to eight lanes, making it a traffic bottleneck. Due to ramps from Highway 427's southernmost segment feeding in, this segment of Highway 401 between Highways 427 and 409 is six lanes per direction, with no express/collector split. Highways 409 is a short freeway used mainly as a spur route for traffic travelling to the airport or Highway 427 northbound from Highway 401 westbound, as these route movements are not accommodated at the junction between Highways 401 and 427.
At the terminus of Highway 409, where the ramps merge into Highway 401, Highway 401 returns to its east–west route through Toronto. This is also the west end of the third, final, and longest express-collector segment, which crosses the rest of Toronto to Brock Road in Pickering in the east. An average of 442,900 vehicles pass between Weston Road and Highway 400 per day as of 2008, making this segment of Highway 401 in Toronto the busiest freeway in the world. In spite of this congestion, it is the primary commuting route in Toronto, and over 50 percent of vehicles bound for downtown Toronto use the highway. The four-way junction with Highway 400 has flyover ramps that favor traffic north of that interchange, as south of that interchange, Highway 400 has an exit to Jane Street before the route continues further south as the municipal expressway, Black Creek Drive. Between the interchanges with Highway 400 and Keele Street is a set of transfer ramps between the express and collector lanes nicknamed "The Basketweave", as each direction has a pair of ramps that cross over and under each other.
Passing between Downsview Airport and Yorkdale Shopping Centre, access for Highway 401 motorists west of Dufferin Street is provided by the latter's partial interchange. Access to Yorkdale for motorists to/from Highway 401 east of Allen Road is provided by the latter's complicated turbine/combination interchange. Between Avenue Road and Yonge Street, Highway 401 crosses North America's busiest multi-structure bridge at Hogg's Hollow.
The four bridges, two for each direction with the collector and express lanes, carried an average of 360,300 vehicles daily in 2019. After passing south of North York City Centre and Bayview Village, the freeway descends as it approaches an interchange with Leslie Street, which provides an exit/entry for North York General Hospital and Oriole GO Station; the Concord Park Place condo buildings are north of the highway. East of the Leslie Street Interchange, Highway 401 ascends as it crosses the Don River and approaches the major junction with Highway 404 and the Don Valley Parkway.
File:Highway 401 Densification.jpg|right|thumb|Highway 401 looking west from Don Mills Road overpass, with the Concord Park Place condo development and North York General Hospital in the background.
Between Birchmount Road and Midland Avenue, Highway 401 is elevated on a berm as it crosses three surface streets and two railway lines. Progressing eastward in Scarborough, the Highway 401 continues through mostly residential areas and Scarborough City Centre including the shopping mall, Scarborough Town Centre. At the northwest corner of the interchange with McCowan Road is a Bell Media/CTV studio complex and CTV Television Network's studio office, 9 Channel Nine Court. Highway 401 eventually reaches Toronto's eastern edge where at Meadowvale Road, it turns southeast briefly before crossing Kingston Road as it swings northeast as Highway 2A merges into it, followed immediately by an interchange with Port Union Road/Sheppard Avenue, then crossing the Rouge Valley into Pickering and Durham Region.
West of Pickering, Highway 401 again meets former Highway 2, which thereafter parallels it to the Ontario–Quebec border. East of Toronto, as the highway approaches an interchange with Brock Road, the collector and express lanes converge, narrowing the 14-lane freeway to 10, divided only at the centre.
It remains this width as it passes into Ajax,
before narrowing back to six lanes at Salem Road.
Planned expansions east of Salem to improve flow leading into the Highway 412 and Lakeridge Road interchanges will see the highway widened to ten lanes as far as Brock Street in Whitby, where the existing interchange will be reconfigured.
East of Ajax, the highway passes through the second rural gap, and enters Whitby. The stretch of Highway 401 through Whitby and Oshawa features several structures completed during the initial construction of the highway in the 1940s. Several of these structures are to be demolished, either due to their age, or to prepare for the planned widening of Highway 401 through this area.
A former Canadian National Railway overpass, which was fenced off but commonly used by pedestrians during Highway of Heroes repatriations, was demolished on the night of June 11, 2011. A second structure in Bowmanville was demolished during two overnight closures on July 9 and 16.
At Harmony Road, the suburban surroundings quickly transition to agricultural land, and Highway 401 finally exits the urban GTA. Encountering another hydro corridor, the highway curves around the south side of Bowmanville, then travels towards Highway 35 and Highway 115.