 The road's westernmost segment was previously named "Post Road" and was extended to Paine Field in the late 1960s, a few years after its interchange with I-5 was opened in 1965.SR 96 was added to the state highway system and codified in 1991, traveling east from I-5 to SR 9 via Mill Creek.Seattle Hill Road was bypassed to the south by Cathcart Way in 2004, planned by the county government since 1978 to redirect traffic on the two-lane SR 96.