The Four Level Interchange is the first stack interchange in the world. Completed in 1949 and fully opened in 1953 at the northern edge of Downtown Los Angeles, California, United States, it connects U.S. Route 101 to State Route 110. In 2006, the interchange was officially renamed in the memory of Los Angeles traffic and weather reporter Bill Keene.

A directional interchange, colloquially known as a stack interchange, is a type of grade-separated junction between two controlled-access highways that allows for free-flowing movement to and from all directions of traffic. These interchanges eliminate the problems of weaving, have the highest vehicle capacity, and vehicles travel shorter distances when compared to different types of interchanges.