1991 was before Metrolink, before the Alameda Corridor, and before the ATSF-BN and SP-UP mergers, all of which have brought big changes to the railroad infrastructure in Southern California.
In 1991, Los Angeles Union Passenger Terminal had only Amtrak service, and was controlled from the signal towers. In 2011, there is Metrolink and Metro Gold Line Service in the main terminal area, with CTC control by Metrolink. IN 1991, the various approach lines were owned by Santa Fe, Southern Pacific and Union Pacific, and controlled by their respective dispatchers in distant locations. Now, all are controlled by Metrolink dispatchers in Pomona, with many more tracks to work with than before..
In those twenty years, SP's Taylor Yard and Diesel Shop have disappeared, and the Metrolink Maintenance Center appeared. Tracks have been at least doubled to the Van Nuys area. Metrolink stations have been added..
Tracks have been relocated in Soledad Canyon, higher track speeds introduced, and Metrolink stations added.
The erstwhile Santa Fe Pasadena line is now the Metro Gold Line to east Pasadena, and is becoming the Metro Gold Line further east. East of Pomona, the line has been subsumed by the Metrolink San Gabriel Valley Line
In 1991, there were the SP State Street Line, the SP Baldwin Park Branch (much of it 10 mph track), and part of the Santa Fe Pasadena Line, all soingle track. Today's heavy-duty commuter line, with many Metrolink stations, is a vastly different place.
The UP-SP merger, and the Alameda Corridor East, have added connections and double track segments, and created grade separations at many road crossings.
This single-track former Pacific Electric line has become part of the Metrolink San Gabriel Valley line.
Metrolink and the SP-UP merger have resulted in more tracks, more track connections, and the addition of Metrolink stations.
The advent of Metrolink has changed a single track line into a largely triple-track line with Metrolink stations.
Transfer of ownership from Santa Fe to Metrolink has resulted in doubling of the track and the addition of many Metrolink stations.
In 1991, there was one UP line, one Santa Fe line, and two SP lines (with two branches) to the harbor from the rest of the trackage in the area. In 2011, the advent of the Alameda Corridor, replacing one of the SP lines, has changed everything, with none of the other lines carrying through traffic, although all are still there. In the harbor area, Harbor Belt Line once provided some of the terminal service, but now Pacific Harbor Lines, which has replaced HBL, provides all of the terminal service south of the Alameda Corridor, in a much more coordinated fashion.
The major change here has been the addition of a third track from San Bernardino to Cajon Summit, for freight capacity reasons, plus the post-merge addition of the Silverwood Connection to the Palmdale Cutoff line.
SP had started to add extra track over Beaumont Hill, but UP has accelereated the process.