Wikipedia site states:
A 3.7-mile (6.0 km) section of the Arroyo Seco Parkway opened on July 20, 1940, connecting Orange Grove Avenue in South Pasadena with Avenue 40 in Los Angeles. The remainder in Los Angeles, from Avenue 40 southwest to the Figueroa Street Viaduct at Avenue 22, was opened on December 30, 1940, in time for the Tournament of Roses Parade and Rose Bowl on New Year’s Day. However, the highway through South Pasadena was not completed until January 30, 1941, and landscaping work continued through September. The final cost of $5.75 million, under $1 million per mile, was extremely low for a freeway project because the terrain was favorable for grade separations.
The Arroyo Seco Parkway, also known as the Pasadena Freeway, is the first freeway in the United States. It connects Los Angeles with Pasadena alongside the Arroyo Seco. It is notable not only for being the first, mostly opened in 1940, but for representing the transitional phase between early parkways and modern freeways. It conformed to modern standards when it was built but is now regarded as a narrow, outdated roadway. A 1953 extension brought the south end to the Four Level Interchange in downtown Los Angeles and a connection with the rest of the freeway system.
The road remains largely as it was on opening day, though the plants in its median have given way to a steel guard rail, and it now carries the designation State Route 110, not historic U.S. Route 66. Between 1954 and 2010, it was officially designated the Pasadena Freeway. In 2010, as part of plans to revitalize its scenic value and improve safety, Caltrans renamed the roadway back to its original name. All the bridges built during parkway construction remain, as do four older bridges that crossed the Arroyo Seco before the 1930s. The Arroyo Seco Parkway is designated a State Scenic Highway, National Civil Engineering Landmark, and National Scenic Byway. It was listed in the National Register of Historic Places in 2011.
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