Which Los Angeles parkway became part of U.S. Route 66 in 1940?

The Arroyo Seco Parkway became part of U.S. Route 66 in 1940.

The parkway, now also known as the Pasadena Freeway, connected Los Angeles with Pasadena through the Arroyo Seco. Its opening represented an early stage in the transition from traditional surface highways to limited-access freeways.

Route 66 used the parkway as urban freeway construction expanded in Southern California. The road carried traffic toward Los Angeles and the wider metropolitan area, helping modernize the western end of the historic highway.

The parkway is historically significant because it predates the national Interstate Highway System. It also illustrates how Route 66 changed over time: parts of the route were widened, realigned, or incorporated into newer high-speed roads before the original designation was retired.