A cloverleaf interchange is a two-level interchange in which all turns are handled by slip roads. To go left, vehicles first continue as one road passes over or under the other, then exit right onto a one-way three-fourths loop ramp (270°) and merge onto the intersecting road. The objective of a cloverleaf is to allow two highways to cross without the need for any traffic to be stopped by traffic lights. The limiting factor in the capacity of a cloverleaf interchange is traffic weaving.
A typical cloverleaf interchange with collector/distributor roads in Cutlerville, Michigan, located at: 42°50′56″N 85°40′43″W / 42.848912°N 85.678689°W / 42.848912; -85.678689
The Kathipara Cloverleaf interchange in Chennai, India
Many old cloverleaf interchanges elongate the ramps in the direction of the surface road. This one in Alhambra, California has been supplemented with collector/distributor roads, 34°04′18″N 118°07′23″W / 34.071659°N 118.122938°W / 34.071659; -118.122938
Opening Europe's first cloverleaf (October 1935) at Slussen, Stockholm, 59°19′14″N 18°04′21″E / 59.32063°N 18.072501°E / 59.32063; 18.072501
In civil engineering, grade separation is a method of aligning a junction of two or more surface transport axes at different heights (grades) so that they will not disrupt the traffic flow on other transit routes when they cross each other. The composition of such transport axes does not have to be uniform; it can consist of a mixture of roads, footpaths, railways, canals, or airport runways. Bridges, tunnels, or a combination of both can be built at a junction to achieve the needed grade separation.
An example of the potential complexity of grade separation, seen in the Jane Byrne Interchange in Chicago
Seven various overpasses for grade separation in Spain near Barcelona
Rail-rail grade separation in Xiaoshan, China
The concept of grade separation includes all transport modes, such as a simple pedestrian bridge over rail tracks.
