The red line was part of the metro rail system, the red cars were the first and fastest rail cars in the early 1900s, they are still using the tracts of the old red car systems. It was the first mass rapid transit system and still using the same tracts for parts of today’s Metro Rail.
LA was the hub and tracks ran out from the center to locations like San Diego, Riverside, and other Southern California areas. Much like a big hub with the spokes running out to major cities. It was pressure by Goodyear Tires and the car industry that got LA to abandon the system.