It replaces the original Colorado Street Bridge, built in 1913 by the City of Pasadena and Los Angeles County.
Strict limitations of topography and a deep ravine within a few hundred feet of the main business section of a city of 100,000 necessitated placing ramps and curves on the deck of a structure whose size and location would ordinarily dictate the design and planning of the entire project.
The immediate proximity of the 1913 structure make the selection of type and architectural design more difficult than usual.
Technical design calculations are further complicated by the curvature and superelevation, excessive width, asymmetry of arch ribs and the magnitude of the structure.
An extensive overview of the planning and engineering of the new freeway bridge can be found in the January-February, 1951 issue of California Highways and Public Works.