The Arroyo Seco Parkway

California's First Freeway

The Arroyo Seco Parkway (Pasadena Freeway) was the first divided-lane, high-speed, limited-access road in the urban western United States and the first stretch of road for what would become the extensive Los Angeles freeway network. The approximately six-mile initial stage of the 8.2-mile roadway, completed in 1940, was envisioned as both a scenic road traversing the Arroyo and a vital traffic conduit linking the expanding cities of Pasadena and Los Angeles. Engineers and planners attempted to blend landscaping and native plants into the overall design while implementing safety features appropriate for high-speed travel.

Construction proceeded alongside the installation of the federally assisted Arroyo Seco Flood Control Channel, necessary to ameliorate seasonal flooding. As road construction proceeded southward towards downtown Los Angeles in the early 1940s, the road began to more closely resemble a high-speed freeway. As a prominent example of the evolution from recreational parkways to more utilitarian high-speed freeways, the Arroyo Seco Parkway marks an important stage in the history of American transportation engineering. The Arroyo Seco Parkway was signed as U.S. Highway 66 from December 30,1940 until October 19, 1963, when AASHTO approved the elimination of U.S. Highway 66 from the Jct. of U.S 95 at Needles to Santa Monica.

In 1999, the Arroyo Seco Parkway from Los Angeles to Pasadena was designated by ASCE as a National Historic Civil Engineering Landmark. On July 23, 1999, the Los Angeles Section of ASCE and Caltrans District 7 staged a plaque-unveiling ceremony at the Casa De Adobe, 4605 North Figueroa Street, Highland Park. The plaque provided by ASCE was unveiled by Dr. Delon Hampton, ASCE's 1999 President-Elect, assisted by Tony V. Harris, District Director of Caltrans District 7.

It was District 7's intent to install the plaque in a public open space near the freeway, but upon inspection of various locations Caltrans was unable to find a location considered safe and convenient for public access, and consequently, the plaque was never installed and was placed in storage at District 7 Headquarters at 100 S. Main Street, Los Angeles, where it has remained since 1999.

The Los Angeles Section's History & Heritage Committee has made plans to install the plaque in a Los Angeles city park adjacent to the freeway near the southerly border of South Pasadena in celebration of the Route 66 Centennial in 2026.

The links below provide specifics of the proposed plaque installation and detailed information on the Arroyo Seco Parkway.

Caltrans Announcement	Caltrans Newsletter	1999 Plaque Unveiling	Recording Project	HAER Report (85 pages)	InterpretiveDrawings (23)

Proposed 2026 Plaque Unveiling Ceremony