The Gold Line's eastward extension towards the City of Whittier may proceed via a subway underneath Atlantic Boulevard, should Metro's Board of Directors adopt a recommendation made by staff members.

In February, Metro announced that it was analyzing a potential alignment running north-to-south down Atlantic, as routes along Arizona and Garfield Avenues. All three options would eventually turn east at Washington Boulevard, with a terminus at Lambert Street in Whittier.

A conceptual plan presented to Metro's Regional Service Council's earlier this month indicates that the staff recommendation will necessitates modifications to current Gold Line service patterns. The existing Atlantic Station is located at-grade at the intersection of Atlantic and Pomona Boulevards. This station would be replaced with a new underground stop a short distance south below Beverly Boulevard.

From Atlantic Station, trains would then proceed below street level, with stations at Whittier Boulevard and the Commerce Citadel. After passing beneath high-tension power lines at Tubeway Avenue, the Gold Line would then transition to an aerial structure along Washington Boulevard. Following a stop at Greenwood Avenue, trains would continue towards Whittier on a mixture of aerial and at-grade tracks.

The Whittier branch is one of two Gold Line extensions which received funding through Measure M, the sales tax initiative passed by L.A. County voters last November. The proposed alignment for the second extension, which would run alongside the SR-60 freeway towards El Monte, remains unchanged from the previous report in February.

According to the service council presentation, Metro staff expects that both extensions could be served with a single maintenance facility at a currently undecided location. A connector track would allow trains to travel between the branches.

The two extensions carry a combined budget of $6 billion; onstruction of the first phase of the extension is expected to occur between 2029 and 2035, although Metro continues to explore opportunities to accelerate that schedule.

The northern branch of the Gold Line, which currently runs between Azusa and Union Station, is also on track for an extension.