In north San Diego County there are nice bikeways parallel to Hwy 78 (Oceanside to San Marcos) and Hwy 56 (Del Mar to Poway). My own commute is about 15 miles along Coast Hwy 101 from Encinitas to the UCSD / Sorrento Valley / UTC / Golden Triangle area. (Various jobs over the decades, all clustered in what is one of San Diego County's largest employment centers.) Others can address commuting in south county, which can also be good. I am simply not familiar with all of the details there.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069