Isn't the Expo successor line to the old Pacific coast line?
The present line, from the point where it turns right from alongside the Harbor Freeway to Santa Monica, mostly follows the alignment of the Pacific Electric's Santa Monica Air Line, a very eccentric curiosity for many years. As early as the 1940's it was down to one trip a day (M-F, inbound AM, outbound PM), which PE tried for many years to abandon (I forget just when they finally succeeded, possibly the late -50's; the primary rail service to Santa Monica was provided on 20-minute headways all day by PE's Venice Short line, mostly in center reservation on Venice Blvd.). As to Mr. Norman's comments above, there is a striking correlation between LA Metro/Metrolink and the old PE; the Blue Line is PE's Long Beach Line; the Red Line essentially duplicates PE's San Fernando Valley Line (albeit in subway) as far as North Hollywood, as does the Orange Line (busway) westward from there; the Green Line is in the median of a freeway which takes a little diagonal dogleg southeast of LAX which occupies a little bit of PE's Santa Ana Line. The Gold Line follows the route of the Super Chief through Pasadena as far as Azusa. Interesting how LA got rid of so much they have since had to restore. As a side note, the old Subway Terminal, now about the only building still standing on Hill St. between 4th and 5th, has been converted to some very upscale rental apartments, with an impressive lobby featuring some PE memorabilia; they make a big selling point of the building's history. In fact, I think the building is still called Subway Terminal, with the original name carved in stone on the front.