Fortunately, California has a (rarely-enforced) mandatory sidepath law for pedestrians, but not for cyclists. When the City of Solana Beach added a Class I multiuse path along the east side of Coast Highway 101, the San Diego County Bicycle Coalition was able to convince them to retain the Class II on-road bike lane, although they went with a code-minimum 1.5M / 5 ft width, even though wider paths are recommended in areas with such heavy bicycle traffic. Across the San Elijo Lagoon, Encinitas has a multiuse trail along the west side of Coast Highway 101. Although the Class II lane here is discontinuous, I always choose the street in both locations, for safety, enjoyment, and efficiency.

In contrast, Oceanside has a wide, lightly-used trail along the San Luis Rey River, roughly paralleling the 65mph Highway 76 expressway. Because of the latter's high-speed merges and diverges, I strongly prefer the multiuse trail, which passes under all major intersections, in this case.

Context ... context ... context!