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Cloverleaf Interchange

A cloverleaf interchange is a two-level interchange in which left turns (reverse directions in left-driving regions) are handled by ramp roads. The objective of a cloverleaf is to allow two highways to cross without the need for any traffic to be stopped by red lights, even for left and right turns. The limiting factor in the capacity of a cloverleaf interchange is traffic weaving.

They are common in the United States and have been used for over 40 years as the Interstate Highway System expanded rapidly. One problem is that, frequently, large trucks exceeding the area speed limit (i.e., 25 mph; 40 km/h) roll over. Another problem is the merging of traffic. For these reasons, cloverleaf interchanges have become a common point of traffic congestion at busy junctions.