We will be passing through Los Angeles Union Station (LAUS) at least once per day during our six days in Southern California.
LAUS is the Amtrak station. Serving the station are the Pacific Surfliners, Coast Starlight, Sunset Limited/Texas Eagle combination, and the Southwest Chief. Except for those Pacific Surfliners that run both north and south of Los Angeles, LAUS is an endpoint station. The run-through Pacific Surfliners must change directions and leave in the direction in which they entered the station area. Those going to or from San Diego must negotiate a 180-degree turn.
All but one of Metrolink's commuter lines start or end at LAUS. (The one that doesn't serve LAUS is the Inland Empire-Orange County Line). None of them are through-routed to another line, most likely due to the 180-degree turn as mentioned above.
There are plans to create run-through tracks that would continue south over US 101 and provide more direct access to and from points south and east, thus elminating the bottleneck that now exists. However this is years away. It would be used by Pacific Surfliners to and from San Diego, the Southwest Chief, and Metrolink's 91 and Orange County Lines.
Many buses serve the station as well, either along the surrounding streets, or at the adjacent Patsaouras Transit Plaza. Amtrak Thruway buses, primarily those that run to/from Bakersfield (connections with the San Joaquins) serve the north side of the station and not the transit plaza.
Finally, it is also served by Los Angeles County Metropolitan Transit Authority (LACMTA, or Metro) trains. The Red and Purple Lines heavy rail stops at a station underneath LAUS, which for the forseeable future is its endpoint station. The Gold Line light rail uses an island platform at the same upper track level as Amtrak and Metrolink, specifically the platform between Tracks 1 and 2. The Gold Line runs north to Pasadena, and as of June 27th, east to East Los Angeles. Thus the transfer between the Red/Purple Lines and the Gold Line is a rather tough one that involves a few levels and some distance between them.
The station itself has 12 tracks one level above the concourse. Tracks 1 & 2 are for the Metro Gold Line, while 3 through 12 are shared by Amtrak and Metrolink trains.