The history of California State Route 274
The 1935 Division of Highways Maps of San Diego County and the city of San Diego display Balboa Avenue as a major locally maintained road from Grand Avenue in the San Diego neighborhood of Pacific Beach east to Morena Boulevard. Balboa Avenue as originally configured intersected US Route 101 (then Legislative Route Number 2) at what is now Mission Bay Drive (then Grand Avenue).
Balboa Avenue can be seen extended east of US Route 101 into neighborhood of Clairemont on the 1958 Division of Highways Map. US Route 101 would become part of Interstate 5 in the coming years after the passage of the 1956 Federal Highway Aid Act.
California State Route 274 was designated by way of 1965 Legislative Chapter 2068. California State Route 274 was originally defined as "Route 5 near Balboa Avenue to Route 103." California State Route 274 can be seen for the first time on the 1966 Division of Highways Map as a proposed highway without an adopted alignment. The proposed alignment of California State Route 274 east of Interstate 5 is shown to overlap the existing corridor of Balboa Avenue.