When I write about cities and cite the bottom-up as well as the top-down forces that shape cities, I usually end up with the conclusion that most of urban form is emergent. Journal referees often challenge all this with references to infrastructure which was presumably installed top-down. The favorite story is usually Manhattan's street grid and the Commissioners' Plan of 1811.
But Los Angeles is different. A friend points me to Reyner Banham's Los Angeles; The Architecture of Four Ecologies, particular its Chapter 4, "The Transportation Palimpsest." There were ox cart and horse trails, including the Camino Real, many of which predated the alignments of railroads. Most of the rails were private, many installed to guide buyers to outlying real estate developments. Many of LA's freeways, most of which came in the 1960s, followed routes quite similar to or nearby the old train tracks.
Banham's Figure 30, "Route Map of the Pacific Electric, 1923" (p. 62-63) has much in common with an LA freeway map of today.
The major spines of the freeway plan are apparently emergent alignments. I would not be surprised if there are stories like this in other places. You can never know enough history.