When the current state highway numbering system was first posted in January 1964, SR began in Central Seattle and headed SE to Renton, then NE to I-90 Exit 15 in Issaquah and ended. Effective April 1, 1992, SR 90 from Central Seattle to the intersection of Martin Luther King Jr Way and Boeing Access Rd at the Seattle/ Tukwila city limits was dropped from the state highway system. Today, SR 900 is 16.20 miles long.
Before 1964, SR 900 had been the Renton branch of PSH 2.
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