The Hollywood Freeway is one of the principal freeways of Los Angeles, California (the boundaries of which it does not leave) and one of the busiest in the United States. It is the principal route over 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. It is the second oldest freeway in Los Angeles (after the Arroyo Seco Parkway).

State Route 170 is a California State Highway in the city of Los Angeles that runs in a north–south direction. It is composed of two distinct sections. The first is the part of Highland Avenue that starts from Santa Monica Boulevard and ends at U.S. Route 101. The second portion is the northern portion of the Hollywood Freeway, starting at the intersection of 101 and SR 134 and continuing to its terminus at the Golden State Freeway (Interstate 5).

The freeway runs from the Four Level Interchange in downtown Los Angeles to the Golden State Freeway in the Sun Valley district of Los Angeles in the San Fernando Valley. From the Four Level Interchange to its intersection with the Ventura Freeway in the southeastern San Fernando Valley (also known as the Hollywood Split), the freeway is signed as part of U.S. Route 101; thereafter, it is signed as State Route 170.

The intersection of the Hollywood and Pasadena Freeways, 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.

The entire route is part of the California Freeway and Expressway System.

Although Highland Avenue starts from south of Wilshire Boulevard, it does not pick up its State Route designation until it meets Santa Monica Boulevard in Hollywood. This portion is unsigned and the only indications that it is a state highway are several reassurance shields on Highland Avenue. Before the freeway, Highland Avenue passes the Hollywood and Highland shopping center as well as the Hollywood Bowl, whereupon it goes directly onto northbound US 101.

SR 170 resumes its northbound route at the junction with the Ventura Freeway. SR 134 heads to the east and US 101 continues to the west. On the southbound side, a sign wrongly indicates "END Route 170," although this may be referring to the end of the freeway portion. Curiously, there is no interchange from SR 134 West to US 101 South. This connector route was put on hold pending the construction of the Laurel Canyon Freeway, which never came to fruition. Motorists intending to go in that direction must exit SR 134 at Cahuenga Blvd., make a left, continue on Lankershim Blvd. and follow the signs near Universal Studios to re-enter on US 101. Likewise, there is no interchange from US 101 North to SR 134 East. Motorists intending to go in that direction must exit US 101 at Vineland Ave., make a right, make another right on Riverside Dr. and enter SR 134 on the left. This interchange is also known as the "Hollywood Split."

SR 170 then continues through the northeastern portion of the San Fernando Valley, finally merging onto northbound I-5. There is no connector route to I-5 South because the angle between the two freeways is too acute.

There are HOV lanes in operation 24 hours a day in each direction of SR-170 between I-5 and the Hollywood Split interchange. As part of the I-5 improvements, construction has begun on the interchange of SR 170 and I-5 to make the current SR 170 carpool lanes connect with the proposed I-5 carpool lanes. This as well as improve traffic flow in and out of the interchange. When the I-5 improvements are completed, SR 170 carpoolers will be able to connect with the I-5 carpool lanes as well as the SR-14 carpool lanes (from the I-5) without merging into regular lanes.

Plans for the Hollywood Freeway officially began in 1924 when Los Angeles voters approved a "stop-free express highway" between Downtown Los Angeles and the San Fernando Valley. The first segment of the Hollywood Freeway built was a one and a half mile stretch through the Cahuenga Pass. That segment opened on June 15, 1940. It was then known as the "Cahuenga Pass Freeway." Pacific Electric Railway trolleys ran down the center of this freeway until 1952. 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. The final section, north of the Ventura Freeway to the Golden State Freeway was completed in 1968.

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. Actor Bob Hope called it the "biggest parking lot in the world" in his routine.

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. The freeway was also designed to curve around KTTV Studios and Hollywood Presbyterian Church. 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.

In 1967, the Hollywood Freeway was the first freeway in California that had ramp meters.

Near the Vermont Avenue exit, there's a seemingly over-wide center strip now filled with trees. This is where the never-built Beverly Hills Freeway was to merge with the Hollywood Freeway. Plans for the Beverly Hills Freeway were halted in the 1970s.

The Hollywood Freeway is an expansion of the original Cahuenga Parkway, a short six-lane freeway that ran through the Cahuenga Pass between Hollywood and Studio City. The Cahuenga Parkway featured Pacific Electric Railway "Red Car" tracks in its median, but by the 1950s these tracks were out of service due to radical reductions in Red Car service. The Pacific Electric right-of-way later accommodated an additional lane in each direction.

The Hollywood Freeway is Routes 101 and 170 from Route 110 (Four Level Interchange) to Route 5.

SR 170 was originally supposed to run from the I-5 interchange to I-405 near the Los Angeles International Airport as the Laurel Canyon Freeway under the Laurel Canyon Boulevard, Crescent Heights Boulevard and La Cienega Boulevard alignments of today. In fact, a portion of La Cienega Blvd. alignment between Manchester Avenue and Rodeo Road was constructed to freeway standards, although it is now an expressway maintained by Los Angeles County.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The entire route is in Los Angeles, Los Angeles County.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The entire route is in Los Angeles, Los Angeles County.