Along the route, the line also serves the cities of Downey, Hawthorne, and Lynwood, as well as several unincorporated communities in the South Los Angeles region including Athens, Del Aire, and Willowbrook.

The fully grade-separated route (essentially a light metro) runs mainly in the median strip of Interstate 105 (the Century Freeway) for its latitude portion and in a mixture of viaducts, embankments, and an open trench for its western leg.

On November 3, 2024, the C and K lines underwent service changes to accommodate pre-revenue testing at the upcoming LAX/Metro Transit Center station, scheduled to open in 2025.

The LAX Automated People Mover, which will offer a connection to the airport's terminals, will begin service at LAX/Metro Transit Center station in 2026.

The entire route of the C Line is grade-separated, with its tracks mostly following the median of Interstate 105 (the Century Freeway) and an elevated guideway.

At Aviation/LAX station, passengers can transfer to any one of several bus lines from different operators, including LAX Shuttle Route M, which provides free service to Los Angeles International Airport.

Construction began in 1987 on the corridor as a light rail line, envisioned as a connection with the bedroom communities in the Gateway Cities along the Century Freeway with the then-burgeoning aerospace center in El Segundo.

Because Caltrans dropped a plan for the freeway to cross through Norwalk to Interstate 5, the line was denied a connection to the then-new Norwalk/Santa Fe Springs Metrolink station.

[14] Additionally, although planners planned to add a spur to LAX, they did not include it in the initial project over fears that commuters would not use the line if they had to go through the airport on the way to work.

[15] The collapse of jobs in the area and the compromises made during construction limited the line's utility, earning it the nickname "the train to nowhere.

However, since its opening, ridership continued growing steadily, peaking at nearly 13 million riders in 2014, prompting Metro to operate two-car trains.

[17] One of the lessons learned from the line, and the Harbor Transitway built at the same time, was that freeway median stations offer a poor rider experience, requiring customers to descend from bridges or climb stairs from dimly lit underpasses to isolated stations in the middle of a noisy and exhaust-ridden freeway.

[17] While stations generally have elevators as a necessary accessibility accommodation, these sometimes fail,[20] and have been known for having sanitation issues; escalators are also often out for maintenance or, with the C Line in particular, only available downward.

Although some early proposals would've sent trains through all three directions of the wye that will connect the existing C Line with the new segment, this was rejected by Metro because it would cause too much wear and tear on the track switch mechanisms.

[25][26] The approved plan would incur higher operating expenses, but board members argued it would retain better transfer opportunities for South Bay residents.

[29] On June 22, 2023, Metro's board of directors officially approved the implementation of Option 2 based on staff recommendation and public opinion.