It breaks the rules, and probably symbolizes how the Bay Area fancies itself above the law and beyond censure. I-238 is more amusing than irritating to me, mainly for the reaction it provokes. No eastbound lanes are required. The purpose of this road is to gradually thin out the horrendous traffic caused by commuters coming from the Pleasanton area to the South Bay, by convincing them to drive I-338. California Department of Transportation, November 1984.
Unnamed sources are either maps or personal experience.