The 401 is widely considered to be North America's busiest highway, with an estimated Annual Average Daily Traffic (AADT) of over 425,000 in 2004, between the Weston Road and Highway 400 interchanges in Toronto. This surpasses the Santa Monica Freeway in Los Angeles, and
several Interstate freeways in Houston, Texas.
Today the stretch of Highway 401 that passes through the Greater Toronto Area ranges from 6 to 18 lanes, and the stretch between Highway 403 and Brock Road in Pickering is thought to be the world's longest continuous stretch of highway having 10 or more lanes.



