 SR 78 begins in Oceanside as a continuation of Vista Way . As it encounters a traffic signal and crosses over I @-@ 5 , the route becomes a suburban freeway traveling east through Oceanside . The freeway loosely parallels Buena Vista Creek before entering the city of Vista . Turning southeast , SR 78 continues into the city of San Marcos near California State University San Marcos and enters Escondido , where it has an interchange with I @-@ 15 . A 2011 Caltrans study estimated that the average commuter encountered a delay of 10 minutes on the portion from I @-@ 5 to I @-@ 15 . After passing the Center City Parkway ( I @-@ 15 Business ) interchange , the freeway abruptly ends at the intersection with Broadway . SR 78 then makes a turn south onto Broadway and continues through downtown Escondido by turning east onto Washington Avenue and south onto Ash Street , which becomes San Pasqual Valley Road . 
