Eric Richardson / blogdowntown

The "double-decker" Seventh Street Viaduct opened in 1927, with the new raised span built atop the existing bridge.

DOWNTOWN LOS ANGELES — On September 19, 1927, the first vehicles made their way across the new Seventh Street Viaduct, a 1580-foot span that greatly sped traffic between Downtown and East L.A. by eliminating at-grade rail crossings.

The city paid just 18 percent of the project's $1.4 million cost. The Union Pacific and Santa Fe railroads each paid 25 percent, the county 18 percent, and Los Angeles Railway the remaining 14 percent.

The viaduct was the third to be opened in the late 1920's, following structures over Macy Street and 9th Street. In all, City Engineer Merrill Butler would eventually end up overseeing the construction of at least nine of the landmark crossings adjacent to Downtown.

In appearance, though, the span across 7th Street was unique. The viaduct has a distinctly double-decker appearance thanks to an early form of adaptive reuse: the existing bridge was already modern and sound, so the design for 7th Street simply built on top of it to create the raised viaduct.