PSH 5 TR became SR 706 in 1964 during the 1964 highway renumbering, in which the Washington State Department of Transportation (WSDOT) replaced the previous system of Primary and Secondary Highways with a new system called State Routes, which is still in use today.
The former PSH 5 TR designation was changed to SR 706 in 1964 as part of a highway renumbering initiative by WSDOT, which shifted from the old Primary and Secondary Highway classification to the present-day State Route system that remains in operation.