An Unavoidable Bottleneck

 

A cloverleaf interchange is a two-level interchange common in the United States for over forty years as the Interstate Highway System expanded rapidly. In 1929, the first cloverleaf interchange built in the United States was the Woodbridge Cloverleaf at the intersection of the Lincoln Highway (Route 25) and Amboy—now St. Georges—Avenue Route 4—now U.S. 1/9 and Route 35—in Woodbridge Township, New Jersey. The first cloverleaf west of the Mississippi River opened in 1931, at Watson Road and Lindbergh Boulevard near St. Louis, Missouri, as part of an upgrade of Route 66. The primary drawback of the classic design of the cloverleaf is that vehicles merge onto the highway at the end of a loop immediately before other vehicles leave to go around another loop, creating conflict known as weaving. Weaving limits the number of lanes of turning traffic. Most road authorities have since been implementing new interchange designs with less-curved exit ramps.