Metrolink recently updated the maps on their website. They definitely need to emphasize the connections—especially since Metrolink only had ONE rail connection with Metro before the Pomona extension.
I've heard that the Pomona Metro station is showing signs of (passenger) life; anyone notice if the Metrolink station is getting a boost from Metro transfers?

Millbrae Station is going to become one of California's most important rail hubs once High-Speed Rail arrives. Unfortunately, it's also one of the Bay Area's most constrained stations.

Today, Millbrae already serves Caltrain, BART, SamTrans, and SFO. In the future, it will also serve California HSR, requiring more tracks and more space. Also, the BART wye into SFO creates awkward transfers for Caltrain passengers and operational inefficiencies for BART.

My proposal/TL;DR: make Millbrae the Bay Area's primary rail-airport interchange by extending SFO's AirTrain to both San Bruno and Millbrae, while simplifying BART operations.

Phase 1: Extend AirTrain to San Bruno

The first step is extending AirTrain about one mile north from the Rental Car Center/Long-Term Parking to San Bruno BART and Tanforan.

Benefits:

• Creates a second rail gateway to SFO during future construction.
• Provides another BART-AirTrain transfer point.
• Opens opportunities for airport airside expansion (more taxi/apron/runway/terminal space), hotels, and a relocated rental car center, etc.
• Reduces pressure on airport roadways by allowing passengers to transfer outside the terminals.

Phase 2: Rebuild the SFO/Millbrae Interface

Once AirTrain reaches San Bruno, the southern leg of the BART wye can be rebuilt with minimal impact on travelers.

Instead of continuing BART south from SFO to Millbrae, AirTrain would use the same corridor and most of the existing structures to reach a new station adjacent to the Millbrae parking garage, connected directly to the existing mezzanine. This would not affect BART, because BART would continue serving SFO directly from the north into SFO, and maintain separate service to Millbrae.

This simplifies BART operations while giving Caltrain and future HSR riders a much shorter transfer to SFO. BART will also keep paying rent to SFO to have a station at the international terminal, keeping SFO happy.

Phase 3: Rebuild Millbrae Station

With AirTrain moved to the eastern side of the station, space is freed for a more efficient Millbrae layout.

That creates room for:

• Additional HSR capacity (4 tracks!), where BART gives up the western platform of their 3 platforms
• Better Caltrain-HSR transfers (potentially cross-platform).
• Direct mezzanine access to AirTrain.

Millbrae is now the region's primary transfer point for HSR, Caltrain, BART, and SFO, with SamTrans buses feeding Millbrae.

Another advantage is that the AirTrain stations at San Bruno and Millbrae can now also serve as pick-up and drop-off locations, as well as bag check locations, making the experience and operations easier for everyone.

Phase 4: Long-Term Opportunities

Once the project is complete, SFO now has the flexibility to do things like:

• Add AirTrain infill stations serving airport employees and nearby development, e.g., in the industrial area north of the airport, around the FedEx or Costco sites.
• Extend AirTrain west toward the office/hotel/YouTube district near I-380 and/or southeast toward the Bayshore hotels (airport-oriented development, anyone??).
• Relocate airport-support facilities (such as the rental car center) to free up land for future airport expansions or improvements.

What's more, because Millbrae becomes the primary transfer hub, San Bruno Caltrain can now be closed, improving travel times for both Caltrain and HSR while maintaining airport access to that area via the extended AirTrain.

Relevant Links:

• SFO AirTrain system
• Caltrain system
• California HSR system
• BART system & BART to SFO
• SFO future plans/airport development plan
• An old post from Caltrain-HSR Compatibility Blog, but still relevant today
• An old post I made on improving Bay Area airport transit that partially inspired this

PS: Feel free to suggest additional links or other content for me to add to the post for reference!

These are system maps of possible future NorCal regional rail expansions.

Image 1: Shows 4 NorCal-wide networks: Capitol Corridor, ACE, SJJPA, and Monterey Bay Rail.

Image 2: The SJJPA currently runs 2 lines: Bakersfield -> Sacramento and Bakersfield-> Oakland. CAHSR will the system mostly obsolete. This is how it could change, with 3 new lines. Focusing on the fats growing northern Central Valley, Gold Runner can increase daily services between merced and Sacramento. The map shows the possible alignment which goes through historic downtowns of every city it serves. A local service can even serve smaller towns like Atwater, Delhi, and others. Gold Runner will be the main Merced to Sacramento Spine that hits up those smaller cities and towns not served by HSR, acting as 'last mile' esque service. But SJJPA's more prominent services would be Delta Runner. This would be the Stockton to SF and Oakland trips. The Stockton -> Oakland service is mostly identical to the current Gold Runner line, but has several additional stations and ends at Stockton Cabral. The second Delta Runner line would utilize the much anticipated Regional Rail Tube that will connect NorCal rail to San Francisco's SalesForce Transit Center. Here, Delta Runner's SF route goes further into the Peninsula terminating at Millbrae/SFO, giving the Stockton area a direct rail line to the SFO airport.

Image 3: ACE is currently one of the poorest rail agencies in the state. But here is how its service lines can be improved. The current Stockton -> San Jose route should be extended to Sacramento. It would also get some new stations. The new Merced-> SF line will be ACE's big thing. While the line won't compete with HSR between SF and Merced, it offers the cities on the route the ability to travel between these cities. A direct San Joaquin County-SF route would be astronomical, and compliment BART. it also connects the South San Joaquin County-Tri-Valley area to major cities like SF, Oakland and Merced directly via rail. ACE will not run Merced to Sacramento, that's where Gold Runner comes in, and they serve many of the same cities so transfering is easy.

Image 4: The Monterey Bay area has fought for rail for a while now. Besides Amtrak Coast Starlight and Caltrain until Gilroy, it has no rail. Here, a Caltrain operated rail service can include 3 lines/branches that meet in Gilroy and terminate in San Jose. First, the Salinas route would follow the in-progress Caltrain Monterey extension, with stations in Watsonville and Castroville. I've also added an Aromas station. Second, a Monterey spur line would be wildly popular, connecting a major beach town to the rest of the region. It would have 2 stations and run to San Jose. lastly, Hollister would get a short shuttle line to Gilroy where passengers can transfer to the Monterey line, Salinas line, or the South County Commuter line.

Image 5: Lastly, Capitol Corridor would be updated with 2 lines and more stations. More importantly, it would have a new route that crosses the Bay and goes into San Francisco and terminates at SFO.

Image 6: The last picture shows all 4 NorCal-wide services with Bay Area-only services like Caltrain and SMART. But even those have expansions. Ideally, Bay Area transit and rail is consolidated, making Caltrain and SMART simply lines under a single agency. New lines area also added like: Dumbarton lines, North Bay lines, Vallejo/Napa lines. with new infrastructure: rail bridges and the regional rail tube.

Notes:

• This network would be worked in with BART, this is why Walnut Creek and San Ramon areas do not have any lines because they would theoretically get BART.
• BART does not go to North bay in this proposal. Regional rail has been given dominion over the North Bay with 3 crossings.
• This map does not show potential express services or special service stations
• This map does not include California High-Speed Rail
• This map does not include the North Valley Rail Project that would extend Gold Runner and ACE to Chico. Ideally, those services would also be in existence.
• This map does not include national Amtrak lines like CA Zephyr and Coast Starlight
• This map uses the same ROW for Gold Runner and ACE in the Stockton to Sacramento segment. ACE currently wants to use an ROW that goes through Sac City College and Midtown to be able to go to Chico. I wanted ACE to go to Sac Valley Station so I didn't include that line, but it is a possibility.
• I have also experimented with a Sacramento area commuter rail system. That is not included here. I can post it separately.