Though signs along the portion from Vermont Avenue west to Pacific Coast Highway (SR 1) in Hermosa Beach along Artesia Boulevard are still signed as SR 91, the California Department of Transportation (Caltrans) no longer controls this portion of the highway, as this segment was relinquished to local jurisdictions in 2003.

In 1997, the California government dedicated the portion of SR 91 between Alameda Street and Central Avenue to former assemblyman Willard H. Murray Jr.

During the 1984 Summer Olympics, a 25 km (16 mi) stretch of the highway was home to the cycling men's road team time trial event.

[9] As the only freeway to link Los Angeles, Orange, and Riverside counties, SR 91 is one of the most heavily congested routes in Southern California.

A weigh station for both directions is located between the Imperial Highway and Yorba Linda Boulevard/Weir Canyon Road exits.

In 2015, Caltrans permanently closed off the Grand Boulevard eastbound exit and westbound entrance to accommodate the widening of the freeway.

The primary purpose of the toll lanes is to provide a faster output for drivers due to the congestion the highway experiences during peak hours, and to promote carpooling.

Entry and exit points for the 91 Express Lanes are only located at their west and east ends, and at the Orange–Riverside county line where the toll road originally terminated before 2017.

In the Riverside County segment, drivers are tolled using a congestion pricing system based on the real-time levels of traffic.

[13][14] The "Silver Lake cutoff", which would save about 90 miles (145 km),[15] was proposed by 1920,[16] and completed in 1925 as an oiled road by San Bernardino County.

The route was added to the federal-aid secondary system in 1926,[24] which helped pay for a mid-1930s widening and paving, including some realignments (parts of the old road are now known as Arrowhead Trail).

There it turned west along US 101 Alternate to near downtown Long Beach, where it ended at SR 15 (Atlantic Avenue), at a terminus shared with US 6.

This development is occurring in or around existing cities such as Riverside, Corona, Moreno Valley, Lake Elsinore, Murrieta, and Temecula.

[41] Typical peak period delays were 30–40 minutes in each direction in the ten miles (16 km) of the tollway before construction.

This original section of the 91 Express Lanes operated between the Costa Mesa Freeway (SR 55) interchange in eastern Anaheim and the Orange–Riverside county line, a distance of about 10 miles (16 km).

In April 2002, the Orange County Transportation Authority (OCTA) reached an agreement in concept to purchase the private toll road project for $207.5 million.

The OCTA took possession of the toll road on January 3, 2003, marking the first time the 91 Express Lanes was managed by public officials.

The clause, which was negotiated by Caltrans and never was brought to the legislature, prevented any improvements along 30 miles (48 km) of the Riverside Freeway to ensure profit for the express lanes.

CPTC filed a lawsuit against Caltrans over freeway widening related to the interchange with the Eastern Transportation Corridor, which was dismissed once the purchase with OCTA was finalized.

[49][50] In 2005, evaluations were made about the feasibility of constructing two tunnels through the Santa Ana Mountains which could carry 72,000 cars per day and allow for a commuter rail service between Corona and Irvine.

Additional study of the Irvine Corona Expressway tunnel project has been deferred until such time as financial considerations improve and/or technological advancements warrant reexamination.

[51] If built, the Irvine-Corona Expressway would follow a similar route to the 91 Freeway and is designed to reduce the growing traffic congestion on SR 91 that prompted the construction of the 91 Express Lanes.

If completed, the Irvine-Corona Expressway is projected to be the longest traffic tunnel in North America, approximately 11.5 miles (18.5 km).

[52] Numerous other projects by the Orange County Transportation Authority are currently underway or in the planning phases for distant completion, some as far out as the year 2030.

[53] 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.