The Transbay Terminal / Downtown Extension can fully accomodate the blended system

When Caltrain electrification and the first phases of High Speed Rail were funded this past summer by the California legislature, the new plan raised questions about whether the Transbay Terminal in San Francisco would be able to accommodate the “blended system”, where by High Speed Rail will use Caltrain’s tracks, largely within the existing right of way.

Under the previous plan, less than half of Caltrain service would start and end at the Transbay Terminal in downtown San Francisco, which is near many more job sites and has much richer transit connections than Caltrain’s current 4th and King flagship station. This was a poor plan for Caltrain and San Francisco. In order to provide the best service for riders, and the highest ridership and revenue for Caltrain, the best plan would be to have almost all trains start and end downtown (with the exception of special Giants trains that can stop at 4th and King).

The mismatch between the plans for Transbay Terminal and DTX are of major concern, since work on the Transbay Terminal is moving forward, although the Downtown Extension of the tracks to Transbay is not yet funded.

Friends of Caltrain asked the technical team at the Transbay project about the mismatch between the old Transbay plan and the blended system. What we learned was very encouraging, but important compatibility issues between Caltrain and High Speed Rail have yet to be resolved.

The good news is that the Transbay Terminal and Downtown Extension will be able to accommodate 100% of the planned service envisioned in the “blended system.” According to Caltrain’s analysis of the potential capacity of a blended system, the corridor can handle up to 6 Caltrain trains per direction per hour, and up to 4 High Speed Rail trains per direction per hour, with the addition of some passing tracks. The DTX/Transbay design can handle this capacity, so there is no need to truncate Caltrain service at 4th and King.

The limit to the number of Caltrain trains that DTX/Transbay can fit is defined by the speed with which Caltrain can turn around trains at the end of the line. The current estimate is that it will take Caltrain 15-20 minutes to turn a train. By contrast, BART can turn trains in 5 minutes – if Caltrain was able turn trains around faster, they could get even more service to and from downtown San Francisco.

Another issue is that the earlier designs reserved some platforms exclusively for Caltrain and others for High Speed Rail. But with the blended system, it is not clear how much High Speed Rail capacity will be needed initially. Caltrain’s analysis shows that without passing tracks, the current tracks can handle 1-2 High Speed Trains per hour per direction, and with additional passing tracks, the capacity is 3-4 High Speed Trains per hour per direction. The first High Speed Trains are not expected to reach San Francisco until 2029 at the earliest. So why reserve capacity for an unknown level of need?

The Transbay engineering team handle this issue by designing the “box” in the building so that platform allocation decisions do not need to be made until later. Once the level of service for Caltrain and High Speed Rail is known, they can assign platforms to the appropriate services.

But why do Caltrain and High Speed Rail need completely separate platform areas in the current designs? It would be much better if any train would be able to stop at any platform, and if riders would be able to transfer between long-distance and local trains simply by walking across platforms. Consistent platforms would also make the system more resilient in emergencies; in case of a backup, a train could stop at any platform.

The main reason is that currently, Caltrain and High Speed Rail have not agreed to have consistent platform heights. The Caltrain High Speed Rail Compatibility blog covered the platform height issue in 2009 and how to solve it in 2010. Even if they had consistent platform heights, they are currently planning segregated platforms because unlike European high speed rail services, California plans to have airport-style security theater.

Now that Caltrain electrification and High Speed Rail are moving forward, it is now time to address the platform issues – we’ll write about that in a separate post shortly.

Throughput into Transbay is being improved moderately by increasing the radius of the throat, from 500 feet to 650 feet, addressing some of the concerns about extremely tight curves. This moderate design change increases the speed to 22 mph in the station throat, and 35 mph in the remaining curves. That is still quite slow.

Is the current S-curve alignment, which is technically challenging to build, and requires trains to go very slowly, really the best and most cost-effective solution? Transbay project observers have been asking that question for years, and now the City of San Francisco has gone public with their concerns about the proposed alignment.

So, good news about the basic capacity of the Transbay Terminal / Downtown Extension to handle the full Caltrain schedule. But there are more issues to address regarding platform height compatibility and perhaps the alignment itself. Stay tuned.