State 90 is a rather odd route as they go in the LA area. 90 was planned to be a full freeway from State 1 in Marina Del Rey to State 91 along Slauson Avenue and Imperial Blvd. Only two small segments were ever built. One is known as the Marina Freeway (Johnny Carson’s famous “Slauson Cutoff”) and the Yorba Linda Freeway. Both segments are very short and serve little purpose as freeways. The Yorba Linda Freeway was built in 1962 with one interchange at Kellogg Drive. The rest of the freeway is two lanes wide with no grade crossings from Yorba Linda Blvd to Esperanza Road. Part of the freeway was built along a Pacific Electric Railway alignment. This section was upgraded to a four lane divided roadway, albeit a narrow one, a couple of years ago.
The Marina Freeway is a full freeway from Culver Blvd to Slauson Avenue. Interchanges exist at I-405 and Centinela Avenue. It was built in stages from 1967 to 1972.
The rest of 90 exists along Imperial Blvd from Beach Blvd (SR-39) to State 91 and is a conventional highway. Imperial is four lanes or more along that segment.
Eastern State 90: Orange County
Western State 90: Los Angeles County