It is the principal route through the Cahuenga Pass, the primary shortcut between the Los Angeles Basin and the San Fernando Valley.

It is considered one of the most important freeways in the history of Los Angeles and instrumental in the development of the San Fernando Valley.

[2] From its southern end at the Four Level Interchange to its intersection with the Ventura Freeway in the southeastern San Fernando Valley (the Hollywood Split), it is signed as part of U.S. Route 101.

The intersection of the Hollywood, Santa Ana, and Harbor freeways and the Arroyo Seco Parkway, known as the Four Level Interchange, is one of the major landmarks in Los Angeles and a symbol of the city's post-World War II development.

In 1970, the definition was amended to subdivide the portion south of US 101 as "(a) Los Angeles International Airport to Route 90."

In 2015, the state relinquished Highland Avenue to the city of Los Angeles, and the legislature amended the definition to reflect that as well as remove the final unconstructed freeway segment.

SR 170 then continues through the northeastern portion of the San Fernando Valley, finally merging onto northbound I-5.

The next section of the freeway that stretched from the San Fernando Valley to Downtown Los Angeles opened on April 16, 1954 at a cost of $55 million.

[2] A year after the Hollywood Freeway opened, it was used by an average of 183,000 vehicles a day, almost double the capacity it was designed to carry.

[2] The segment through Hollywood was the first to be built through a heavily populated area and requiring the moving or demolition of many buildings, including Rudolph Valentino's former home in Whitley Heights.

[2] Much of the rubble and debris from the buildings removed for the freeway's construction was dumped into Chávez Ravine, the current home to Dodger Stadium.

California's legislature has relinquished state control of the segment of SR 170 along Highland Avenue, and thus that portion is now maintained by the City of Los Angeles.

[12] Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage.