SR 506 begins at Ryderwood and heads east via Vader to Jct I-5 at Exit 59 just north of the I-5 bridges over the Cowlitz River. It may appear that this interchange is the eastern terminus of SR 506 but it is not. SR 506 continues north up the west side of I-5 to Exit 60 and ends. Before 1992, SR 505 used to begin where SR 506 ends. SR 506 is signed from I-5 at Exit 59, though, not Exit 60. SR 506 is 11.53 miles long.
Before 1964, SR 506 had been SSH 1P.
Primary State Hwys Secondary State Hwys