Cloverleaf Interchange - Overview

Overview

Cloverleaf interchanges, viewed from overhead or on maps, resemble the leaves of a four-leaf clover. In the United States, cloverleaf interchanges existed long before the interstate system. They were originally created for busier interchanges that the original diamond interchange system could not handle. Their chief advantage was that they were free-flowing and did not require the use of such devices as traffic signals. This not only made them a viable option for interchanges between freeways (where such devices are typically not an option), but they could also be used for very busy arterials where signals could present congestion problems.

They are very popular 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 (see below). For these reasons, cloverleaf interchanges have become a common point of traffic congestion at busy junctions.

At-grade cloverleaf configurations with full four leafs and full outside slip ramps are extremely rare, though one exists in Toms River, New Jersey. Any other intersections with merely one, two, or three leaf ramps with outer ramps would not be designated a "cloverleaf" and simply be referred to as a Jughandle intersection.