 SR 78 is part of the California Freeway and Expressway System , although only the metropolitan section of SR 78 is a freeway . The section of SR 78 from the western junction of SR 79 to the western junction with SR 86 is designated by the California State Legislature as eligible by law for the State Scenic Highway System ; however , only the section in Anza Borrego Desert State Park has officially been designated by Caltrans as being part of the system , meaning that it is a substantial section of highway passing through a " memorable landscape " with no " visual intrusions " , where the potential designation has gained popular favor with the community ; it gained this status in 1971 . SR 78 from I @-@ 5 to I @-@ 15 , and from the eastern junction with SR 86 to the eastern junction with SR 111 is part of the National Highway System ( NHS ) , a network of highways that are essential to the country 's economy , defense , and mobility . In 2013 , SR 78 had an annual average daily traffic ( AADT ) of 670 between the San Diego – Imperial county line and the western SR 86 junction , and 163 @,@ 000 between Twin Oaks Valley Road and Nordahl Road , the latter of which was the highest AADT for the highway . 
