Predecessors Highway 401's history predates its designation by over two decades. As automobile use in southern Ontario grew in the early 20th century, road design and construction advanced significantly. Following frequent erosion of Lake Shore Road, then
macadamized, a concrete road known as the
Toronto–Hamilton Highway was proposed in January 1914. Construction began on November 8 of that year, following the onset of . The highway was designed to run along the lake shore, instead of
Dundas Street to the north, because the numerous hills encountered along Dundas would have increased costs without improving accessibility. Middle Road, a dirt lane named because of its position between the two, was not considered since Lake Shore and Dundas were both overcrowded and in need of serious repairs. The road was formally opened on November 24, 1917, Over the next decade, vehicle usage increased substantially, and by 1920, Lakeshore Road was again congested, particularly during weekends. In response, the Department of Highways examined improving another road between Toronto and Hamilton. The road was to be more than twice the width of Lakeshore Road at and would carry two lanes of traffic in either direction. Construction on what was then known as the
Queen Street Extension west of Toronto began in early 1931. Before the highway could be completed,
Thomas McQuesten was appointed the new minister of the Department of Highways, with
Robert Melville Smith as deputy minister, following the
1934 provincial elections. Smith, inspired by the German
autobahns—new "dual-lane
divided highways"—modified the design for Ontario roads, and McQuesten ordered the Middle Road be converted into this new form of highway. A
right-of-way was purchased along the Middle Road and construction began to convert the existing sections to a divided highway. Work also began on Canada's first
interchange at Highway 10. When widening in Scarborough reached the
Highland Creek ravine in 1936, the Department of Highways began construction on a new bridge over the large valley, bypassing the former alignment around
West Hill. From here the highway was constructed on a new alignment to Oshawa, avoiding construction on the congested Highway 2. drawing highway engineers from across North America to discuss the new concept of "Dual Highways". On the first day of the convention, McQuesten announced his vision of the freeway: an uninterrupted drive through the scenic regions of Ontario, discouraging local business and local traffic from accessing the highway except at infrequent controlled-access points. It was announced in the days thereafter this concept would be applied to a new "trans-provincial expressway", running from Windsor to the Ontario–Quebec border. Highway engineers evaluated factors such as grading, curve radius, and the narrow median used along the Middle Road—which was inaugurated on August 23, 1940, as the
Queen Elizabeth Way (QEW)—and began to plan the course of a new dual highway mostly parallel to Highway 2, with precedence given to areas most hampered by congestion. Unlike the QEW, this highway would not be built along an existing road, but rather on a new right-of-way, avoiding the need to provide access to properties. Highway 2S (S for
Scenic) was the first completed section of new roadway. Built to connect with the
Thousand Islands Bridge at
Ivy Lea and opened as a gravel road in late 1941 or early 1942, the road followed the shore of the Saint Lawrence River and connected with the western end of the twinned Highway 2 near Brockville. In addition, the highway between Highland Creek and Oshawa was opened as a gravel-surfaced road in May 1942. Following the war, construction resumed on roadways throughout Ontario. The expressway between Highland Creek and Oshawa was completed in December 1947 and designated as Highway 2A, the Highland Creek to Oshawa expressway (Highway 2A) and Highway 2S were designated
Controlled-Access Highway No 401, Construction was completed for several sections of the Toronto Bypass: between Highway 400 and Dufferin Street in August, west to Weston Road in September, east to Bathurst Street in October and finally to Yonge Street in December. A stub of Highway 2A which was not incorporated into Highway 401 remained a provincial route as a connector to Kingston Road. Extensions east and west began in 1953; the eastern extension to Bayview Avenue opened in April 1955, and the highway was opened between Weston and Highway 27 in September 1955. was completed in August 1956. as did the
Kingston Bypass in Eastern Ontario. Work began to connect the latter with the
Scenic Highway in 1955. Michigan officials encouraged Ontario to bypass
Highway 3 as the most direct path from
Detroit to Buffalo. By 1956, construction had begun on a segment between Highway 4 in London and Highway 2 in Woodstock, as well as on the section between Windsor and Tilbury. and the Ontario–Quebec boundary, it serves the richest economic region in Canada. In January 1965, it was named by The Honourable
John Robarts, Premier of Ontario, in honour of the two founding architects of the Confederation of Canada, Sir John A. Macdonald and Sir George-Étienne Cartier. This site is located on the last section of construction, consisting of 15 miles between Ivy Lea and Highway 2, which was completed on October 11, 1968.|A plaque near Brockville commemorates the official completion of the highway. In 1958, a section bypassing
Morrisburg was opened to accommodate traffic displaced from a portion of Highway 2 through
The Lost Villages of the
Saint Lawrence Seaway. By the end of 1960, the Toronto section of the highway was extended both eastwards and westwards: first east from Newcastle to Port Hope on June 30; then later west from Highway 25 in Milton to Highway 8 south of Kitchener on November 17. The gap between Woodstock and Kitchener was completed on November 9, 1961, while the gap between Tilbury and London was completed two lanes at a time; the westbound lanes on October 22, 1963, the eastbound on July 20, 1965. The final sections, from west of Cornwall to Lancaster, were opened between 1962 and 1964; two lanes opened to Lancaster on September 11, 1962, but the other two were not completed until July 31, 1964. The last segment, to the Ontario–Quebec boundary, was opened on November 10, 1964. However, by then numerous properties and a tourist industry were established, which had not been present when the parkway originally opened in 1938.
James Auld, MPP for Leeds and the
Minister of Tourism and Information, joined local residents to persuade the DHO to construct an inland bypass. The DHO agreed, stating that it would cost less to build a new freeway than to upgrade the parkway. Construction of the
Thousand Islands Bypass began in 1965, with work proceeding east from Gananoque. The Thousand Islands Parkway was the final two-lane segment of Highway 401. A portion was opened on September 1, 1967, from Gananoque to Highway 137, which was itself built south to the parkway at the same time. The Highway 401 designation was applied along this new route, while the bypassed portion of the parkway was redesignated as Highway 2S. Despite the expected influx of traffic from the United States for
Expo 67 in Montreal, the DHO opted to build the portion east of Ivy Lea after the centennial celebrations. Finally, on October 11, 1968, the
Thousand Islands Bypass opened. Unlike other names later applied to the highway, the "Macdonald–Cartier Freeway" designation covers the entire length of Highway 401. Signs designating the freeway and shields with the letters "M-C" were installed, but these had been removed by 1997. In 2003, 38 years after Robarts' naming of the highway, a
Member of Provincial Parliament attempted to get the "Macdonald–Cartier Freeway" highway name enshrined into law; the bill only passed first reading and was not enacted. In the 1970s, Highway 401 was widened to six lanes in Durham. Between 1977 and 1982, Highway 401 was widened from four to six lanes between Hurontario Street (Highway 10) to Highway 25, with the Jersey median barrier making its debut in Ontario in that segment. For Highway 403, the Highway 410 interchange was a better connection point than the original suggested terminus at the Highway 401-427 interchange, but would also require the widening of Highway 401 between Highway 403 and Highway 427 from eight lanes to an eighteen-lane collector-express system. Plans were submitted and approved in December 1977 by Mississauga city council, and construction began. The first section of Highway 403 between Cawthra Road and Highway 401 was opened August 18, 1980; the original connecting ramps were built on the outer perimeter of the interchange to serve what would later be designated as the collector lanes of both routes, leaving sufficient right-of-way between for future ramps linking the express lanes of both routes. The 1980s saw more sections of Highway 401 widened. Most significant was the new collector-express system between Highway 403 / 410 and Highway 427. This including a new set of flyover ramps from the express lanes to Highway 403 which opened in 1984, while a basketweave transfer between the eastbound collector and express lanes near Pearson Airport was completed in mid-1985. At this time, the Highway 401 express lanes merged/diverged into/from the collector lanes east of Tomken Road which resulted in a temporary left-handed exit/entry for the ramps to/from the Highway 403 express lanes. After the Kennedy Road overpass was replaced, cast-in-place post-tensioned concrete flyover ramps were constructed from 1988 to late 1990 to link up Highway 401 and Highway 410, notably the 11-span
flyover ramp from Highway 401 eastbound to Highway 410 northbound which remains the longest in the Greater Toronto Area, while the Highway 410 southbound to Highway 401 eastbound flyover replaced a loop ramp. In the fall of 1991, alongside the widening of Highway 410 into a full freeway, construction began on the connecting ramps between Highway 403 and Highway 410, made possible by the removal of the loop ramp (see above) which pass under the existing bridge structures carrying Highway 401 which would soon be designated as the collector lanes. In 1993, new overpasses crossing Tomken Road and the connecting ramps between Highway 403 and Highway 410 were constructed for the Highway 401 express lanes, extending Highway 401's collector-express system from east of Tomken Road to just east of Kennedy Road. Plans were made to extend the eastern system from Toronto's Neilson Road to Pickering's Brock Road in the late 1980s, but took over a decade to reach fruition by 1997. This was followed shortly thereafter by the widening of the highway through Ajax and a new interchange at Pickering Beach Road (renamed Salem Road) and Stevenson Road. The 1990s also saw the first step in widening the highway from Toronto to London, by replacing the grass median with the addition of a third traffic lane per direction separated by a tall-wall concrete median barrier. The segment from London to Woodstock received this upgrade first, with the expansion shortly east of the split for Highway 403's newly constructed western segment. A project in the mid-1990s brought the highway up to a minimum of six lanes between Highway 8 in Kitchener and Highway 35 / 115 in Newcastle. Other projects prepared sections for eventual widening. In its 2007 plan for southern Ontario, the MTO announced long-term plans to create
high-occupancy vehicle (HOV) lanes from Mississauga Road west to Milton; by 2011 these plans had been expanded in scope to as far west as Hespeler Road in Cambridge. From the mid-1990s onward, several prerequisite projects were undertaken for the future widening of Highway 401 throughout Milton and Mississauga, although that section of the freeway would retain its six-lane cross section for at least the next decade. This included the new interchange with the upcoming Highway 407 ETR (with a temporary diversion for the eastbound lanes to facilitate construction of the post-tensioned flyovers), a new underpass structure to accommodate Derry Road which was widened from two to six lanes (1996–97), the addition of an interchange with the
Mavis Road extension in 1999, whose overpass was designed to be lengthened with two outer spans, and replacing the Mississauga Road overpass and interchange which began on February 15, 2002 (in a cost-sharing agreement between the province and
Peel Region) and completed in 2003. Starting on August 19, 2009, Highway 401's collector-express lanes in Mississauga have been extended westward beyond its initial terminus at
Highway 410. Tying into this extension of Highway 401's collector-express system, the missing ramps from Highway 401 eastbound to Highway 403 westbound and the opposite movement were completed in 2018 The first phase of this expansion to west of Hurontario Street, a distance of , opened in 2013, while the second phase to the Credit River was completed in 2020. In 2019, an announcement was made for expanding the freeway from the Credit River to Regional Road 25 in Milton to a minimum of 10 lanes, including HOV lanes. This project included extending the existing 12-lane collector–express system from the Credit River to just east of Winston Churchill Boulevard, while another 12-lane collector–express system was built from just west of the Highway 407 interchange to just east of James Snow Parkway, due to the overpasses for Highway 407 and the adjacent Winston Churchill Boulevard not being constructed wide enough to accommodate a continuous collector–express system underneath. Sections of the new expansion were opened overnight throughout the second half of 2022. On August 13 and 14, 2022, the westbound express lanes opened between Highway 407 and James Snow Parkway. The remainder of the westbound lanes, between the Credit River and Winston Churchill Boulevard, were opened several months later on November 13 and 14. The eastbound express lanes between James Snow Parkway and Winston Churchill Boulevard were opened a week later on November 18 and 19, and from Winston Churchill Boulevard to the Credit River on November 29 and 30. The HOV lanes in both directions were opened on December 9, 2022. The remaining works of this project, including final layers of paving, culvert works, and carpool lots were completed on October 19, 2023, thus completing a 14-year project that expands the highway from Highway 410 to Regional Road 25 that started on August 19, 2009.
COMPASS cameras In early 1991, Highway 401 was equipped with a traffic camera system called
COMPASS. 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.
Advantage I-75 Between June 1990 and 1998, Highway 401 and
Interstate 75 were used for a pilot project named
Advantage I-75 to test the reliability and versatility of an automated tracking system for transport trucks. Termed "MACS" (Mainline Automated Clearance System), it allows a truck to travel from Florida to Ontario without a second inspection. MACS was initially tested at two truck inspection stations in
Kentucky, with transponders installed in 220 trucks. Exact time, date, location, weight and axle data were logged as a truck approached an equipped station. Following initial tests, MACS was deployed at every inspection station along I-75 from Miami to Detroit, and along Highway 401 from Windsor to Belleville in 1994.
"Carnage Alley" The section of Highway 401 between Windsor and London has often been referred to as
Carnage Alley, in reference to the numerous crashes that have occurred throughout its history. The term became more commonplace following several deadly
pileups during the 1990s. The nature of that section of highway, described as a mainly straight road with a featureless agricultural landscape, was said to make drivers feel less involved and
lose focus on the road. In winter, the area between Woodstock and Chatham is also subject to sudden snow squalls from lake-effect snow. Several collisions have resulted from motorists deviating from their lane and losing control of their vehicles. Various other names, including
The Killer Highway circulated for a time, but
Carnage Alley became predominant following an 87-vehicle pile-up on September 3, 1999 (the start of
Labour Day weekend), the worst in Canadian history, that resulted in eight deaths and 45 injured individuals. with then-
Highway 98 (now Provincial Road) in the foreground, and the split at
Dougall Parkway in the background. This segment would be reconstructed in 2008–10. Only a few days prior, then-Transportation Minister
David Turnbull had deemed the highway "pleasant" to drive. On the morning of September 3, the local weather station reported clear conditions due to a malfunction, Immediately following the crash, the MTO installed paved shoulders with
rumble strips and funded additional
police to patrol the highway, a move criticized as being insufficient. Beginning in 2004, of the highway was widened from four asphalt lanes to six concrete lanes, paved shoulders were added, and a concrete Ontario Tall Wall median was installed, which was the solution the
Canadian Automobile Association promoted in 1999. From 2008 to 2010, with joint funding from the provincial and federal governments, the section of Highway 401 from Dougall Parkway (the former Highway 3B) to Provincial Road (the former Highway 98) was widened to six lanes, necessitating the replacement of several underpasses including those of Walker Road and Provincial Road. The loop ramp from Provincial Road southbound to Highway 401 eastbound was removed, although the rest of the interchange remained unchanged. As part of that project, the Dougall Parkway split with Highway 401 was reconfigured, replacing a one-lane 1950s-era underpass tunnel with a modern high-speed flyover ramp from Dougall Parkway that joins the eastbound freeway lanes on the right-hand side. The old interchange had reduced Highway 401 eastbound traffic to one lane as it merged with the left-hand on-ramp from Dougall Parkway, whereas the new interchange allows three lanes per direction of Highway 401 to pass through. West of the reconstructed Dougall Parkway onramp, Highway 401's grass median was replaced with a concrete barrier but continued to be striped for two lanes per direction until the North Talbot Road overpass was replaced and Phase One of the Highway 401 extension (
Rt. Hon. Herb Gray Parkway, formerly
Windsor-Essex Parkway) (see below) opened in 2015, allowing for a continuous six lane freeway cross-section.
Highway of Heroes On August 24, 2007, the MTO announced that the stretch of Highway 401 between Miller Road in Trenton and the intersection of Highway 404 and the Don Valley Parkway in Toronto would bear its additional name,
Highway of Heroes (French:
Autoroute des héros), in honour of Canadian soldiers who have died, though Highway 401 in its entirety remains designated as the
Macdonald–Cartier Freeway. This length of the highway is often travelled by a
convoy of vehicles carrying a fallen soldier's body, with his or her family, from the military airport at
CFB Trenton to the coroner's office at the
Centre of Forensic Sciences in Toronto. Since 2002, when the first fallen Canadian soldiers were repatriated from
Afghanistan, crowds have lined the
overpasses to
pay their respects as convoys pass. for the Highway of Heroes|alt=A Highway of Heroes reassurance marker with a red poppy flower in place of a number. Above that is the text
Highway of Heroes, and below it
SUPPORT OUR TROOPS. The origin of the name can be traced to an article in the
Toronto Sun on June 23, 2007, by columnist Joe Warmington, in which he interviewed Northumberland photographer Pete Fisher. Cobourg resident Ron Flindall was responsible for organizing the first bridge salutes following the loss of four soldiers on April 18, 2002. Warmington described the gathering of crowds on overpasses to welcome fallen soldiers as a "highway of heroes phenomena". This led a
Cramahe Township volunteer firefighter to contact Fisher on July 10 about starting a petition, leading Fisher to publish an article which was posted to the
Northumberland Today website. The online article eventually caught the attention of London resident Jay Forbes. Forbes began a petition, which received over 20,000 signatures Following the announcement on August 24, the provincial government and MTO set out to design new signs. The signs were erected and unveiled on September 7, On September 27, 2013, the
Highway of Heroes designation was extended west to
Keele Street in Toronto, to coincide with the move of the coroner's office to the new Forensic Services and Coroner's Complex located at Highway 401 and Keele Street.
Highway improvements and safety concerns London and Kitchener and
Wellington Road in
London. Additional widening west of Highway 402 is planned. Between 2006 and 2008, Highway 401 was widened from four to six lanes between Highway 402 and
Wellington Road in London. This included reconfiguring the Wellington Road interchange from a cloverleaf to a Parclo A4 while replacing the original 1956 overpass with a longer and wider structure. The project included the installation of a tall-wall median barrier, straightening curves and adding additional interchanges on the freeway, allowing it to be easily vacated in an emergency event.
Greater Toronto Area Beginning in 1998, several projects were initiated on Highway 401 within Toronto. In 2000, near the Allen Road interchange, the westbound express-to-collector transfer (meant to serve motorists on the express lanes wishing to get off at Keele Street, but turned out to be lightly used) was closed off and replaced by a new collector-to-express transfer. From 2005 to 2007, the Hogg's Hollow bridges were rehabilitated and the Yonge Street underpasses were replaced, with the structure carrying the eastbound collectors being widened from two to three lanes through the interchange with Yonge Street.The most significant construction work was widening the route from six to eight lanes though the Highway 427 interchange in 2005, which necessitated the replacement of the Highway 27 underpass, although the rest of the junction's flyovers could accommodate the expansion. and rehabilitating the flyover ramps of the Highway 401 / 400 interchange. . On August 10, 2008, following a series of
explosions at a propane facility in Toronto, Highway 401 was closed between Highway 400 and Highway 404 as a precautionary measure, the largest closure of the highway in its history. The highway remained closed until 8 p.m., though several exits near the blast remained closed thereafter. In Oshawa, exit 416 (Park Road) was replaced by a new interchange at exit 415 (Stevenson Road). The contract, which began September 7, 2005, included the interchange and the resurfacing of of the highway between Oshawa and . The westbound ramps were opened in mid-September 2007 and the eastbound ramps in mid-2009. The resurfacing was completed mid-2010. The interchange to Highway 412 opened on June 20, 2016. Highway 401's interchange with Highway 418 (East Durham Link) opened on December 9, 2019, alongside the opening of an eastern extension of Highway 407.
Rt. Hon. Herb Gray Parkway , opened in 2015, showing the below-grade portion with tunnels and greenspace. It will connect to the
Gordie Howe International Bridge. Highway 401, as originally completed, did not have direct access to the Canada–United States border, as upon entering the Windsor city limits, the route terminated at a
semi-directional Y interchange where the freeway defaulted into Highway 3. Traffic continuing to the border had to follow the non-express Highway 3 routing along Talbot Road and Huron Church Road which had a dozen traffic lights. The approach to the
Ambassador Bridge was heavily built up making it impractical to twin the existing crossing and reconstruct the approach as a freeway to meet growing demand for cross-border traffic, even though Ambassador Bridge owner
Matty Moroun had long lobbied for this. In 2004, a joint announcement by the
federal government of the United States and
Government of Canada confirmed that a new border crossing would be constructed between Detroit and Windsor. The Detroit River International Crossing (DRIC) was formed as a bi-national committee to manage the project. The MTO took advantage of this opportunity to extend Highway 401 to the Canada–US border and began an
environmental impact assessment on the entire project in late 2005. On February 8, 2008, the MTO announced it had begun purchasing property south of the E. C. Row Expressway, upsetting many area residents who had purchased properties in the years prior. On March 3, 2008, the
Michigan Department of Transportation and the MTO (in partnership with
Transport Canada, the
Federal Highway Administration of the United States and the Detroit River International Crossing group) completed a joint assessment on the soils along the Detroit River and determined they could indeed support the weight of a new bridge; the stability of the underlying soil and clay and the impact of the nearby
Windsor Salt Mine had caused concern for all parties involved in the project. Despite protest from area residents, as well as a dismissed lawsuit from Ambassador Bridge owner Matty Moroun, On November 28, 2012, the Ministry of Transportation announced that a Federal
Order in Council was passed to change the name of the parkway to the "Rt. Hon. Herb Gray Parkway", in honour of
the Right Honourable Herb Gray, a
Member of Parliament from Windsor. The Highway 401 extension (
Rt. Hon. Herb Gray Parkway, formerly
Windsor-Essex Parkway, MTO internal designation of Highway 7901 The Highway 401 extension would have six through-lanes, and the section parallel to Highway 3 is below-grade with 11 covered tunnels ranging from in length. The Highway 401 extension features of green space and over of recreational trails, with seven bridges and two tunnels separating the trails from roads. Interpretive signage includes information about
First Nations in Canada,
Tallgrass prairie and the
Carolinian landscape. Initial construction of a
noise barrier from North Talbot Road to Howard Avenue began in March 2010; full construction began on August 19, 2011. The original North Talbot Road overpass was demolished on August 20, 2011, to make way for the widening of the existing freeway from four through-lanes, however the replacement bridge was closed in December 2013 due to faulty concrete girders and rebuilt by May 2014. Progress on the freeway extension was delayed as the construction consortium disposed of over 500 concrete girders (including the 320 girders already installed), after a Ministry of Transport investigation found that these girders manufactured from a partnership of Freyssinet and Tierra Armada did not meet standard, and replaced by those from Prestressed Systems Inc. at no cost to the public. The Highway 401 extension was built on a new alignment while Highway 3 (Talbot Road) was also rerouted, so the old interchange of Highway 401 at Highway 3 remained in service until it was bypassed once the extension and replacement interchange opened. The old interchange as well as the signalized intersection at Outer Drive has since been removed. In early 2015, it was announced the first phase of the Highway 401 extension would open to traffic between Highway 3 and Labelle Street (near the E. C. Row Expressway) in the spring; an section was opened to traffic on June 28, 2015, extending Highway 401 as far west as the E. C. Row Expressway, the first new segment of Highway 401 to be opened since the Thousand Islands Parkway bypass in 1968. The first phase of the Highway 401 extension provides an express bypass to much of (but not all of) Highway 3 en route to the Ambassador Bridge. The E. C. Row still lacked direct access to the London-bound portion of Highway 401, however, the indirect connection using Huron Church Road was reduced to a short distance (with one traffic light) between the Parclo A4 interchange with the E. C. Row and the slip ramps to the first phase of the Highway 401 extension. The second phase of the Highway 401 extension to Ojibway Parkway was opened on November 21, 2015 completing the Highway 401 extension as far as the planned bridge approach and border plaza. Crossing the Detroit River, the new bridge will extend Highway 401 across the Canada–US border to a spur connection through Delray to I-75. Construction on projects related to the Gordie Howe International Bridge began in 2015 with an initial completion date in 2019–20. The Gordie Howe International Bridge was substantially completed in early 2026, with an opening date to be announced. in response to the higher-than-average accidents occurring on the "Carnage Alley" stretch including the 1999 Labour Day weekend pileup. West of Essex County Road 42 on the west of Tilbury, the highway has been widened to six lanes with a concrete divider in anticipation of the Rt. Hon. Herb Gray Parkway. As of 2022 the MTO has initiated studies on widening 118 km of the freeway from four to six lanes between Tilbury and London through four contracts. Around London the traffic volumes are expected to increase considerably, so the province established an extensive plan to widen and reconstruct the London corridor between 2006 and 2021. This included building a new interchange with
Wonderland Road which opened in November 2015 to help improve access to Highway 401 westbound from the city's southwest end and involved replacing the Westminster Drive overpass to allow the highway to be widened. A reconstruction of the outdated
cloverleaf interchange at
Colonel Talbot Road and widening Highway 401 from four to six lanes between
Highway 4 and Highway 402 is also proposed. The MTO is also planning on widening Highway 401 from six to eight lanes through part of the London corridor. Alongside the extension of the Veterans Memorial Parkway (formerly Airport Road) south of the freeway to Wilton Grove Road in 2017, the Parkway's trumpet interchange was reconfigured from a trumpet to a Parclo with the replacement overpass able to accommodate future freeway expansion. In the Kitchener/Cambridge area, the widening of Highway 401 from six to twelve lanes from Highway 8 (King Street) to Highway/Regional Road 24 (Hespeler Road) commenced on June 8, 2015, and concluded in summer 2019. The new HOV lanes from Highway 8 to Townline Road opened on December 22, 2023. Just west of the Highway 8 interchange, the freeway's existing six-span Grand River Bridges (opened in 1960, restriped in the early 1990s from two to three lanes per direction) are being replaced with two new four-span structures, a project scheduled for completion in 2025. The new Grand River bridges are a prerequisite to the planned expansion of the Y-junction between Highway 401 and Highway 8 Expressway from a partial to an all-directional interchange, with proposed flyover ramps linking eastbound Highway 401 to Waterloo-bound Highway 8 and the opposite movement to bypass the existing non-express connection using King Street. A Transportation Environmental Study Report was completed on widening highway 401, extending the collector-express system easterly through to the Highway 412 interchange in Whitby, then ten lanes easterly to Liberty Street in the Municipality of Clarington. The assessment was completed in March 2015. To support this widening, all of the original overpasses dating back in the 1940s and 1950s built through Whitby and Oshawa were replaced with new overpasses as part of contemporary highway safety standards and to allow for a future highway widening.
Eastern Ontario East of Durham, the MTO widened parts of Highway 401 to six lanes. as well as the Salmon River bridge between Belleville and Napanee. By 2020, the highway was widened to six lanes for through Kingston between exits 611 and 623, 16 years after it started back in 2004. Construction began in 2014 to expand the highway to six lanes approximately east of exit 474 in Cobourg.
Proposed tunnel On September 25, 2024, Premier
Doug Ford announced that the Ontario government has launched the technical evaluation for the proposed construction of a new driver and transit tunnel expressway under Highway 401. == Services ==