ATSF's subsidiary did from 1888 to 1895, but...it got washed out to sea every winter. However Metrolink and OERM put most of what's left to good use!

Also it wouldn't reduce traffic much, as only four or so freights run the LOSSAN, and at that they don't come into play until the Olive Sub flows in at Orange (save for the 5th La Mirada but that never affects anything). They aren't long ones either, on Sunday for example the M-SDGBAR was comprised of two engines and five cars when it passed San Juan, and was running about three hours early (no work in Stuart Mesa).

The big issue is commuter trains, especially those which lay over on the main line. Metrolink has a number of trains which stopover at various points on the line. The worst offender has to be Irvine--despite having only three or four trains making turnarounds there, unlike Mission Viejo or Fullerton it has no pocket tracks for a turning train--the station is thus effectively reduced to single track. That should change when a third main from CP Bake to CP Aliso is installed.

I think the rest of the reductions in travel time will be from reducing the amount of single track. Pulgas - Don and several of the lagoon doubletrackings come to mind. And north of LA you have Raymer - Bernson being upgraded too!