The Four Level Interchange, first stack interchange in the world opened in Los Angeles.

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.

Los Angeles, often referred to by its initials L.A., is the most populous city in the U.S. state of California, and the commercial, financial, and cultural center of Southern California. With an estimated 3.88 million residents within the city limits as of 2024, it is the second-most populous in the United States, behind New York City. Los Angeles has an ethnically and culturally diverse population, and is the principal city of a metropolitan area of 12.9 million people (2024). Greater Los Angeles, a combined statistical area that includes the Los Angeles and Riverside–San Bernardino metropolitan areas, is a sprawling metropolis of over 18.5 million residents.

September 22 is the 265th day of the year in the Gregorian calendar; 100 days remain until the end of the year.