A unique running opportunity in San Diego is the ‘coaster”, which involves taking the Coaster train north from Solana Beach and then running back on the Coast Highway. One can go as far as Oceanside, which is 16 miles. There is a shoulder/bike lane along the road most of the way. The road alternates between some lovely oceanside sections and some parts that are a bit inland or where the water is blocked bu homes or businesses. We’ve also used some more local shore roads which are closer to the water in sections. Bring money…and water!
From Solana Beaach, follow the coast highway. In Encinitas, you’ll get off the Coast Highway and follow some local roads (Neptune Ave. for a couple of miles). In Carlsbad, use Carlsbad Blvd. Then use Pacific Ave. in oceanside.
Nicest sections are near Solana Beach, and in Carlsbad. Note: If running from Torrey Pines to Solana Beach, not a very attractive stretch.