The network is situated almost entirely in Southern Ontario, although Highway 400 extends into the more remote northern portion of the province.

Modern 400-series highways have high design standards, speed limits of 100 kilometres per hour (62 mph), with a 110 kilometres per hour (68 mph) limit on select stretches, and various collision avoidance and traffic management systems.

As a result, they currently experience one of the lowest accident and fatality rates comparative to traffic volume in North America.

[6] McQuesten also sought out the economic opportunities that came with linking Toronto to Detroit and New York state by divided roadways with interchanges at major crossroads.

[32] Other major works included the skyway bridges along the QEW and the expansion of Highway 401 through most of Toronto into twelve-lane collector–express systems.

Interchanges tend to be spaced at least 1.5 kilometres apart in urban areas unless there are basket weave ramps or collector lanes to facilitated shorter merge distances.

The Institute of Traffic Engineers subsequently recommended this design to replace the cloverleaf interchange throughout North America.

"[54] A 110 km/h (68 mph) trial was set up on three stretches of highways on September 26, 2019, to test the viability of increasing speed limits.

[57][58] On October 2, 2024, Premier Doug Ford mentioned in a press conference that he had directed Transportation Minister Prabmeet Sarkaria to raise the speed limit on all remaining 400-series highway sections “where it is safe to do so”.

[59] Conforming with the Manual on Uniform Traffic Control Devices, Ontario utilizes green signs for guidance purposes, including distances to nearby interchanges and destinations.

[60] Generally, blue signage is used to list services and attractions at upcoming exits, known as Tourism-Oriented Directional Signing.

[60] The baseline standard for the construction of or expansion to a freeway in Ontario is an average daily traffic count of 10,000 vehicles per day.

[62] The MTO plans and finances the construction and maintenance of the King's Highway system, which includes the 400-series network.

Highway 401 is the longest freeway at 828.0 kilometres (514.5 mi), in addition to being the widest and busiest road in Canada.

In May 2007, the MTO introduced a multibillion-dollar Horseshoe Network Project, which included plans to incorporate HOV lanes into numerous 400-series highways.

The Highway 427 extension, which opened on September 18, included an HOV lane north of Finch Avenue.