The Metro zone fare policy is praised for being simple, and indeed it is, even if it’s still wedded to the idea that all the jobs are in Seattle (Metro, unlike Sound Transit, doesn’t have different zones for East and South King County). If you cross the Seattle City Line, you pay a two-zone fare.
But what happens when a route drives along the city line? I found out the answer when I found myself on the 124 to the Museum of Flight. In this stretch, the east side of the road is in Seattle but the west side is in Tukwila.
Metro has resolved this dilemma by charging you a two-zone fare when you leave the border area, regardless of which direction you go. If you think it through, it’s a solution that successfully avoids any possible fare-avoidance shenanigans using Link.