Ontario Highway 401

Highway 401
Macdonald–Cartier Freeway
Highway 401 highlighted in red
Route information
Maintained by the Ministry of Transportation of Ontario
Length	828.0 km[1] (514.5 mi)
History	Proposed 1938 Opened December 1947 – October 11, 1968[2] Extended June 28 and November 21, 2015
Major junctions
West end	Ojibway Parkway – Windsor
Major intersections	E. C. Row Expressway – Windsor  Highway 402 – London  Highway 403 – Woodstock  407 ETR – Milton   Highway 403 / Highway 410 – Mississauga  Highway 427 – Toronto  Highway 400 – Toronto  Highway 404 / Don Valley Parkway – Toronto   Highway 35 / Highway 115 – Clarington  Highway 416 – Johnstown
East end	A-20 – Quebec border
Location
Country	Canada
Province	Ontario
Major cities	Windsor, London, Kitchener, Cambridge, Mississauga, Toronto, Oshawa, Kingston and Cornwall
Highway system
Ontario provincial highways Current Former 400-series
← Highway 400 → Highway 402
Former provincial highways ←  Highway 400A

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,^[3] is a controlled-access 400-series highway in the Canadian province of Ontario. It stretches 828 kilometres (514 mi) 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,^[4][5] and one of the widest.^[6][7] 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 (MTO) and patrolled by the Ontario Provincial Police. The speed limit is 100 km/h (62 mph) throughout its length, with the only exceptions being the posted 80 km/h (50 mph) limit westbound in Windsor and in most construction zones, along with a 110 km/h (68 mph) speed limit between Windsor and Tilbury.^[8]

By the end of 1952, three individual highways were numbered "Highway 401": the partially completed Toronto Bypass between Weston Road and Highway 11 (Yonge Street); 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 11.8, 54.7, and 41.2 km (7.3, 34.0, and 25.6 mi), respectively. In 1964, the route became fully navigable from Windsor to the Ontario–Quebec border. In 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 817.9 km (508.2 mi) length. Since 2007, a portion of the highway between Trenton and Toronto has been designated 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.

Highway 401 previously ended at Highway 3 (Talbot Road) upon entering Windsor. In 2011, construction began on a westward extension called the Rt. Hon. Herb Gray Parkway (formerly Windsor-Essex Parkway). This extension runs parallel to Highway 3 (Talbot Road and Huron Church Road) 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 8-kilometre (5.0 mi) section of the parkway, east of the E. C. Row interchange, opened 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 to Townline Road in Cambridge to at least ten lanes was completed by 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 Oshawa. The expansive twelve-plus-lane collector–express system through Toronto and Pickering, and partially across Mississauga, was extended west to Milton in December 2022.