Fantastic 360 view of driving Ontario's HWY 400

King's Highway 400 is the primary north-south highway route from Toronto to Central and Northeastern Ontario's vast recreational and resort areas. Since the highway's completion between Toronto and Barrie in 1952, the highway has steadily increased in importance, and it has now become one of Ontario's most essential transportation corridors. The road carries thousands of holiday-bound motorists every weekend, in addition to countless numbers of weekday commuters who work in the Greater Toronto Area but prefer the leisurely lifestyle of cottage country. The highway also carries a considerable volume of trucks to and from Ontario's resource-rich north. This highway has had a profound impact on the accessibility of northern recreational areas for tourists and cottagers alike.

The new Highway 400 provided a fast through route which bypassed all of the towns between Toronto and Barrie. Initially, the entire highway was four lanes, with two lanes provided for each direction of travel. The dual carriageways were separated by a narrow grass median. Two new highway service centers, a first for Ontario, were constructed along Highway 400 in 1953-1954. One was located at the King City Sideroad Cloverleaf, selling Shell Oil Products, while the other was located at the Cookstown Road (Highway 89) Cloverleaf selling British-American Oil products. The Cookstown Service Centre operated continuously for nearly 60 years until it was closed and relocated to a new site further north in 2013. The King City Sideroad Service Centre was closed and relocated to a new site near Kirby Road during the 1970s.

The completion of the Trans-Canada Highway to Sudbury in the late 1950s prompted highway designers with the DHO to plan for a northerly extension of Highway 400 to provide improved access to Sudbury. The Highway 400 Extension continued north from Barrie and joined up with the Trans-Canada Highway near Coldwater. The Highway 400 Extension was initially completed as an undivided two-lane highway. Still, sufficient right-of-way was acquired so that the highway could be expanded to four lanes in the future. The Highway 400 Extension from Barrie to Coldwater was completed and opened to traffic on December 23, 1959. Initially, the DHO had envisioned Highway 400 continuing northeasterly from Coldwater to Gravenhurst. In the early 1960s, the proposed highway corridor was surveyed, and plans for the new CAH were designated. The new route would have connected to Highway 11 just south of Gravenhurst. However, the proposed highway corridor between Coldwater and Gravenhurst was never built. By the mid-1970s, the proposed Coldwater-Gravenhurst route had been superseded by a new route for Highway 400 from Coldwater to Waubaushene, linked directly to Highway 69. It was felt that this new Highway 400 route via Waubaushene, in conjunction with improvements to the Highway 11 corridor, would best serve the highway transportation needs of this area.

Highway 400 was also extended southerly from Highway 401 to Jane Street in the mid-1960s as part of creating a large network of freeways across Toronto. The Highway 400 South Extension to Jane Street was officially opened to traffic on October 28, 1966. The plan to extend Highway 400 south from Jane Street towards Downtown Toronto was extensively revised during the 1970s when many of the proposed Toronto freeway projects were being canceled. The proposed Highway 400 Extension to Weston Road was scaled back considerably. Ultimately, it was constructed as a limited-access arterial road in the late 1970s and early 1980s. The road was known initially as the Northwest Metro Arterial Road but was later renamed Black Creek Drive. The province transferred ownership of Black Creek Drive to Metropolitan Toronto on February 25, 1982.

The speed limit on Highway 400 is 100 km/h (60 mph) unless posted otherwise.