Up here in North County you can forget public transit, believe me I’ve tried; I love public transportation having lived in NYC and San Francisco.
However my husband and I did manage to do just fine with one car and public transportation for five years up here in North County. I don’t work but use the car mostly to get the kids to school, etc.. I would either take my husband to/from work or he’d use public transportationif possible. Sometimes it was inconvenient but whenever I thought about getting a second car it didn’t seem worth it.
Now my husband works in east San Clemente and there’s not a workable public transit option so we got a second car.
The point is that maybe some of these 2+ car families could use public transportation but keep one car for those trips to Mira Mesa at night.
I do believe that in San Diego County it would be impossible to rely solely on public transportation, you do need a car to fall back on.