The King's Highway 401 (also known as the Macdonald-Cartier Freeway) is a highway that extends across Southern Ontario, Canada. It is the longest 400-Series Highway in Ontario, and one of the widest and busiest highways in the world. In fact, the highway has the distinction of being North America's busiest freeway. Together with Quebec Autoroute 20, it is the road transportation backbone of the Quebec City-Windsor Corridor, along which over half of Canada's population resides. Colloquially, the road is known simply as the 401, spoken as "four-oh-one."
On August 24, 2007, the stretch of highway between Toronto (from Highway 404/Don Valley Parkway) and Trenton (from Glen Miller Road) was given the additional name Highway of Heroes, in honour of Canadian Forces personnel killed during the War in Afghanistan. Along the route are several heritage sites, an international bird watching area, saline lakes, as well as regional and provincial parks. Museums and historical markers commemorate the region's history along the highway.
