Wash. Rev. Code § 47.17.595
A state highway to be known as state route number 405 is established as follows: Beginning at a junction with state route number 5 in the vicinity south of Seattle, thence northeasterly to Renton, thence northerly east of Lake Washington to a junction with state route number 5 north of Seattle.
[ 1970 ex.s. c 51 s 120.]