The 400-series highways always have a minimum 4 lane cross-section with grade separation at all junctions. Interchanges tend to be spaced at least 1.5 kilometres apart in urban areas unless there are basket weave ramps or collector lanes to facilitate shorter merge distances. In rural areas, interchanges tend to be spaced at least 3 kilometres apart, although exceptions exist. When the cross-section of highway is larger than 10 lanes, the road is usually arranged into a
local–express lane system, which exist on sections of Highways 400, 401, 403, 404 and 427. On all but a few interchanges in the whole system, ramps merge freely on the highway except if there are
ramp meters in use, and stop or yield controlled ramps are rare. An interchange with stop-controlled ramps onto Highway 400 at Canal Road was permanently closed on 10 June 2025. While older freeways have some lapses in safety features, contemporary 400-series highways have
design speeds of ,
speed limits ranging from to , various collision avoidance and traffic management systems, and several design standards adopted throughout North America. Of note are the
Ontario Tall Wall median barrier and the
Parclo A-4 interchange design, the latter which became standard in the design for the widening of Highway 401 through Toronto in 1962. The
Institute of Traffic Engineers subsequently recommended this design to replace the cloverleaf interchange throughout North America. Ontario highways rank fourth in North America for fatality rates, with 0.61 fatalities per 10,000 licensed drivers in 2017. However, this also includes two-lane provincial highways. On May 1, 2019, the government of Ontario was looking towards raising the speed limits of the 400-series highways up to
Jeff Yurek, Transportation Minister at that time had stated that "The 400-series highways were built for, I believe, a speed limit of 120 km/h safely." A trial was set up on three stretches of highways on September 26, 2019, to test the viability of increasing speed limits. The three trialed sections along with three more sections were permanently changed to the higher speed limit on April 22, 2022, and two more sections were trialed. The two trialed sections were made permanent along with 10 more sections on July 12, 2024. 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”. Conforming with the
Manual on Uniform Traffic Control Devices for Canada, Ontario utilizes green signs for guidance purposes, including distances to nearby interchanges and destinations. Generally, blue signage is used to list services and attractions at upcoming exits, known as
Tourism-Oriented Directional Signing. However, several exceptions exist, notably blue guidance signage for toll highways such as
Highway 407, in addition to the
collector lanes of highways. The MTO plans and finances the construction and maintenance of the King's Highway system, which includes the 400-series network. The system includes of freeways. Highway 401 is the longest freeway at , in addition to being the widest and busiest road in Canada. Highway 420 is the shortest of the routes at .) and therefore is built to 400-series standards but lost its QEW designation after being downloaded to the City of Toronto. The section of
Highway 7 between the town of
Carleton Place and its junction with Highway 417 is also built to 400-series standards, but a 400-series designation has yet to be applied.
Highway 69 between Sudbury and Key River is built to 400-series standards in anticipation of it becoming part of Highway 400 once the gap between the two freeways is filled.
Highway 115 north of Highway 35/Highway115 concurrency and Peterborough is also built to 400-series standards, however a 400-series designation has yet to be applied. Most other freeways and expressways in Ontario that lack a 400-series designation have lower construction standards, lower design speeds and lower speed limits. == High-occupancy vehicle lanes ==