Regarding the discussion about the Pacific Electric Red Cars, it's important to note that a lot of the lines ran on very different service levels.
Many of the longer ones, such as that giant line out to San Bernardino, were "interurbans." These are rather similar to what we think of today as "commuter rail," such as Metrolink.
Look at this record of the timetables at
http://www.erha.org/pelines/pensb.htm
10 trains from SB to LA, and 10 trains back, per day.
Now look at today's Metrolink service from SB to LA. 19 trains in, 19 out. Plus, more trains that go SB to OC, Riverside to LA, etc.
Now, obviously it's not quite S-Bahn or RER level service (which is really what any commuter rail service should be pursuing) but you get really reliable frequencies on close in stations that are serviced by multiple lines. Glendale, Norwalk, Downtown Burbank, etc you get trains every 5-10 minutes at rush hour, and at a so-so pace throughout the rest of the day.
I think that, plus the 56 miles of Metro "Liner" (Orange and Silver lines) gives a more complete view of the rapid transit network.