A system interchange is a three-dimensional intersection providing continuous and rapid traffic conversion functions between highways, and primary roads with trunkline functions.

It is located at intersections of two or more highways and is exclusively used for vehicle transitions between highways. Generally, it does not have toll stations and does not connect with local road networks.

The system interchange serves as a three-dimensional intersection for the mutual crossing of highways or other multi-lane roads with trunkline functions. It functions as the highest-level node in the road network system, facilitating the critical role of traffic flow conversion between trunk highways.

The system interchange adopts a three-dimensional intersection type to ensure all traffic flows freely. The access forms of entering and exiting traffic flows on the intersecting roads mainly involve merging and diverging, ensuring that through traffic has absolute priority.

Typical system interchanges include the three-fork Y-type, three-fork T-type, four-fork direct-cross type, turbine shape, complete cloverleaf shape, modified cloverleaf shape, and combination types.

Intersections are critical points in traffic management, providing convenience for vehicles and pedestrians to adjust their directions. However, the presence of traffic signals at intersections somewhat reduces the road's capacity.

While roundabouts can alleviate traffic congestion at intersections, they may still be inadequate when facing high traffic volumes. Analysis suggests that when the traffic flow at an intersection reaches 4,000 to 6,000 vehicles per hour, a three-dimensional intersection, commonly called an "overpass," is needed. Its primary advantage lies in avoiding time constraints imposed by traffic signals, allowing traffic from different directions to flow independently without interference.

The interchange overpass has relatively complete traffic capacity and functionality among various forms of overpasses. Also known as a system interchange, it connects multiple roads with ramps, allowing vehicles to change directions on roads at different heights and orientations quickly.

While the traffic capacity of system interchanges is significant, they require extensive space and investment. Depending on traffic characteristics, incomplete system interchanges can be designed by limiting turns in specific directions or reducing the number of ramps.

System interchanges can be classified into various types based on design and functionality. Examples include cloverleaf interchanges suitable for highways or suburban ring roads, trumpet interchanges for three-fork intersections, directional interchanges with multiple dedicated lanes commonly used for highways, and spiral interchanges ideal for extending the route of left-turning vehicles.

Round interchanges are more suitable for complex intersections with multiple forks, ensuring smooth flow through traffic on main roads.

In summary, different system interchanges have distinct functions, and their design should be based on actual traffic conditions.