Planning for SR 56 started in 1956, according to San Diego Councilwoman Barbara Warden. The route was first added to the California State Highway System in 1959 as Legislative Route Number 278 (LRN 278). The routing ran from LRN 2, which later became US 101, all the way east to LRN 198, which is now SR 67. In the 1964 state highway renumbering, LRN 278 was renumbered SR 56 and was designated to run from I-5 to SR 67. On December 30, 1980, the City of Poway included SR 56 in their city plan extending all the way east through the city to a northern extension of SR 125. In 1983, both the cities of San Diego and Poway supported the extension of SR 56 all the way to SR 67, although Poway wanted the route moved and had reservations about the freeway ending in their city. Nevertheless, there are no plans to construct the portion of SR 56 east of I-15; several arterial roads connect the eastern end of the SR 56 freeway with SR 67, including Ted Williams Parkway, Twin Peaks Road, Espola Road (CR S5), and Poway Road (CR S4).