Secondary State Highway 5I

SSH 5I was added to the state highway system in 1937. This route began at Jct SSH 5H in Yelm and headed northwesterly, ending at Jct PSH 1 (US 99) in Tumwater. In 1959, the route was changed so that the highway ran from Yelm via Lake St. Clair to Jct PSH 1 (I-5/US 99) at Exit 107 in Lacey. In 1967, the northwest terminus of SSH 5I, by now signed as SR 510, was moved again, this time to Jct PSH 1 (US 99/US 410) in the Hawks Prairie area on the east side of Lacey. The following year the terminus was moved a fraction of a mile north to Jct I-5 when the I-5 freeway opened between Exits 109 and 114. Today, SSH 5I is SR 510.