SSH 11A was added to the state highway system in 1937. The route was originally described in state law from east to west, beginning at Jct PSH 11 (US 395) at Connell and ending at Jct PSH 3 (US 97/US410, now I-82/US 12/US 97) in Yakima. When the Hanford Reservation was created during World War II, the portion of SSH 11A that crossed the reservation was closed to the public.
In 1957 the portion of SSH 1A from SSH 11G (now SR 17) to Connell was transferred to SSH 11B.
In 1961, the route description in state law was changed to read from west to east. Provisions were made for rerouting SSH 11A east of Cold Creek via a bridge at Vernita, replacing a ferry and opened to traffic in 1965, to Jct SSH 7C (now SR 26) at Othello. Also, provisions were made to drop that portion of SSH 11A from the former ferry landing at White Bluff to Jct SSH 11G (now SR 17) at Mesa from the state highway system upon completion of SSH 11C (now SR 240) from SSH 11A near Cold Creek to Richmond. This link was completed and the provision took effect in 1967.
When the current state highway route numbering system was first posted in January 1964, the Yakima to Othello portion of SSH 11A was assigned the number SR 24. The section of SSH 11A from White Bluffs to Mesa became SR170.
Primary State Hwys Secondary State Hwys