The Ridge Route opened in 1915, with concrete paving completed in 1919. The Ridge Route was designated as US 99 in 1926. Construction of the three-lane US 99/Ridge Route Alternate through Piru Canyon began in 1930 to address the engineering limitations of the orginal Ridge Route and ever-increasing traffic load, and was completed in October 1933. The third (middle lane) was for passing in either direction, a common highway design in the 1930s, and was colloquially known as the 'Suicide Lane'. Widening to four lanes began after World War II and was completed in 1952. Upgrading to freeway/Interstate standards began in 1963 and the eight lane Interstate 5 was finished in 1970. Interestate 5 generally follows the Ridge Route Alternate right-of-way except for around and above Pyramid Lake, where now a section of the Ridge Route Alternate lies submerged. A vast upthrust of eocene shale is seen along the US 99/Ridge Route Alternate in Piru Canyon in Ventura County. April 15, 1937.
Roads--California--Ventura County Geology--California--Ventura County Ventura County (Calif.) Ridge Route (Calif.) Works Progress Administration Collection photographs
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