Wash. Rev. Code § 47.36.022
The duration of a yellow change interval at any traffic control signal must be at least as long as the minimum yellow change interval identified in the manual of uniform traffic control devices for streets and highways as adopted by the department under this chapter.
RCW 47.36.022
Findings-Intent- 2012 c 85 : "The legislature finds that it is in the interests of the driving public to continue to provide for a uniform system of traffic control signals, including provisions relative to yellow light durations, fine amounts for certain traffic control signal violations, and signage and reporting requirements at certain traffic control signal locations. The legislature further finds that a uniform system of traffic control signals greatly enhances the public's confidence in a safe and equitable highway network. Therefore, it is the intent of the legislature to harmonize and make uniform certain legal provisions relating to traffic control signals." [2012 c 85 s 1.]