The Richards Boulevard Underpass is a concrete structure that carries railroad traffic over Richards Boulevard with a simple, industrial character. The load is carried by means of steel I-beams which rest on concrete abutments to support a wood plank floor on which three sets of tracks are laid. It was built in 1917 by the California Highway Commission as part of State Route 6, with the cost being born equally by the State and the SP Railroad Co. Although the materials in the floor and the ties, etc. have been replaced many 4 times, the structure possesses a high degree of integrity, location, materials, workmanship, design, feeling and association. In the context of highway construction in California, it appears to be one of the oldest surviving examples of the use of I-beam construction on a railroad grade separation and the oldest in association with the SP system in California. Most grade separation projects undertaken in the pioneer era of state highway construction have been destroyed by subsequent highway widening projects, a concept repeatedly defeated by Davis voters prior to its designation on the National Register. State Route 6 was replaced by US 40, and signs along the “Historic US Hwy 40” are now up, including the route through Davis. The route was also part of the Lincoln Highway for a time and concrete markers designate that route as well.