Due to congestion, several alternatives are being discussed to expand the freeway portion past its current end in Newport Beach.

Following the 19th Street intersection, SR 55 becomes an eight-lane below-grade freeway that bisects the northbound and southbound lanes of Newport Boulevard until the Mesa Drive undercrossing.

Following this, the freeway continues almost due north until reaching its northern terminus at SR 91 near the Santa Ana River.

A HOV lane has been built along the entire freeway portion from I-405 to SR 91, with some direct access ramps, including one for I-5.

However, congestion is still very prevalent throughout the day, as is the norm with many Orange County freeways; Route 55 experiences a peak daily traffic volume of 262,000 vehicles and 17,292 trucks.

It was built from the southern terminus of SR 1 (the Pacific Coast Highway, or "PCH") and continued northbound on roughly the same route it follows today,[10] following Newport Road (today Newport Boulevard) northeast to Tustin, and then Tustin Avenue north to near its current terminus at SR 91.

Between 1996 and 2002, the fifth lane in both directions was constructed between I-5 and SR 91, funded with a sales tax of half a cent approved by Measure M.[16] In April 2007, the Orange County Transportation Authority approved funds to study the feasibility of extending the Costa Mesa Freeway south to 17th Street via tunnels or flyover ramps.

[19] On May 21, 2021, a road rage incident occurred in which the perpetrator fatally shot 6-year-old Aiden Leos, a passenger in his mother's car as it was traveling on the 55 Freeway.