Arroyo Seco Parkway

The Arroyo Seco Parkway, formerly known as the Pasadena Freeway, is the first freeway in California and the western United States. It connects Los Angeles with Pasadena alongside the Arroyo Seco seasonal river. 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 It conformed to modern standards when it was built, but is now regarded as a narrow, outdated roadway.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 most recently to concrete barriers, 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.