Phase 3 was not implemented, and planning stopped after 2009. Phase 3 ran through dense residential areas, so alignment must be considered carefully to avoid adversely impacting those neighborhoods. CTA estimated that Phase 3 would be far more costly than Phase 2 due to its being underground. After a number of alternate plans were evaluated, in 2009 CTA adopted the "locally preferred alternative" (LPA), which stopped Circle Line work after Phase 2, and Phase 3 was relegated to a "long term vision".