Joe Biden administration commits $3.4 billion in funding to San Francisco Caltrain extension

So Caltrain electrifying the corridor is a pretty big deal and will increase ridership. See the section below for more information. And extending an electrified corridor to this station will enable connections to California High-Speed Rail, whose ridership in the San Francisco through Central Valley sections (pp. ES-2) is expected to be about 16.2 million annually base, or a maximum of 53.4 million annually. So that's a lot of people, many of whom would make it all the way to downtown SF.

As for Caltrain specifically, the rolling stock investments they're making for electrification (see below) would not dramatically increase passenger capacity in the car interiors or anything. However, as a result of electrification, they would run quite a few more trains. And if you read Caltrain's executive planning documents, they are quite worried about their low ridership. This connection to the downtown will increase their income substantially and perhaps enable the purchase of more electric trains in the future. Regardless, the electrified line is introducing higher frequencies than present.

Numerically, for the DTX... the San Francisco County Transportation Authority has definitely done ridership forecasts for the Portal/Downtown extension. The document Downtown Rail Extension (DTX) Program Review (2019) says... nothing useful. There were ridership forecasts made in 2019 or earlier, because they're referenced in this document, but without a URL. The content should be somewhere on the TJPA Documents page...

• DTX Design Criteria Dec 2022: DTX Design Criteria Dec 2022 refers to updated ridership estimates still being needed but doesn't actually provide any of the old ones (from 2019 or earlier)
• AHA The CEQA Addendum to the 2018 Transbay Program Final Supplemental EIR: CEQA Addendum to the 2018 Transbay Program Final Supplemental EIR (or use the non-download link) refers to various ridership figures.

The report shows that 63.3 percent of Caltrain riders would use the Transit Center and 36.7 percent would use the Fourth and Townsend Street Station. The 2018 TJPA report also presents an HSR ridership forecast based on the CHSRA’s 2016 Business Plan and a sensitivity analysis test; however, the CHSRA has since updated the HSR ridership forecast using its 2020 Business Plan. The HSR ridership forecast based on the 2020 Business Plan shows that 89.1 percent of HSR riders would use the Transit Center and 10.9 percent would use the Fourth and Townsend Street Station.

As presented in the 2018 Final SEIS/EIR, Caltrain ridership and associated effects on automobile, transit, pedestrian, and bicycle circulation would be reduced in the vicinity of the Fourth and Townsend Street intersection with implementation of the DTX, because passengers would shift to the Transit Center. The TJPA and CHSRA’s latest ridership forecasts confirm that of the total 27,570 daily Caltrain riders and 18,163 daily HSR riders, approximately 33,642 passengers (63.3 percent of Caltrain riders and 89.1 percent of HSR riders) would board at the Transit Center (Cambridge Systematics 2018, CHSRA 2022b). The remaining 12,091 passengers (36.7 percent of Caltrain riders and 10.9 percent of HSR riders) would board at the Fourth and Townsend Street Station. Under a 2040 No Project condition, the Revised Project is not implemented, meaning there would be no Caltrain or HSR passengers boarding in the Transit Center, and all 45,733 Caltrain and HSR riders would board at the existing Fourth and King Station. Implementation of the Revised Project would contribute substantially to reduced ridership at the Fourth and King Station area (due to the shift in ridership to the Transit Center) by approximately 74 percent from 45,733 daily riders to 12,091 daily riders and associated travel demand.

This is from an environmental review, which is why it refers to the reduced ridership of nearby stations. I wish it just said directly what the numbers of new transfers expected at the station would be, but you can judge the potential increase in ridership based on the percent of people using each mode connecting to that station (and nearby stations) to get a sense.

Ok, and it shouldn't have been this hard for me to find the actually quite accessible report on the Final EIS (from 2018), but it says:

The 2004 FEIS/EIR included qualitative and quantitative estimates of changes in transit ridership as a result of the Caltrain extension to the Transit Center. Overall, it was estimated that ridership would increase for Bay Area Rapid Transit (BART) to the East Bay, Alameda–Contra Costa Transit District (AC Transit), and Golden Gate Transit as a result of the increased connectivity between the providers. Similarly, the addition of HSR service to downtown San Francisco would bring more riders (in addition to any new riders resulting from Caltrain service) to the transit providers that operate nearby (FRA 2010a). FRA’s 2010 Final Program EIS Reevaluation, updating the 2004 FEIS/EIR, increased high-speed train ridership estimates over those from the 2004 FEIS/EIR and identified the means of access to the Transit Center. In the 2010 Final Program EIS Reevaluation, forecasts of the number of passengers per day arriving by different transit operators to serve the high-speed train alone in 2035 (FRA 2010a) include San Francisco Muni, 12,000; BART to/from East Bay, 2,000; AC Transit, 2,000; and Golden Gate Transit, 1,000.

Those numbers are a little bit old, but they get the point across.

CAPACITY AND ELECTRIFICATION-RELATED REMARKS

Caltrain is not at ridership capacity. Its ridership is still below that of pre-pandemic levels. Caltrain projects about "20% growth [in ridership] with electrification and 10% annual growth through FY33." This will result in about 80% of pre-pandemic ridership, assuming no other changes to the system are made. This is a high-level planning document and not the actual analysis.

In general (simplifying), we have these things to consider about hard train system capacity:

• Number of distinct tracks on which to run trains without colliding
• Spacing of trains between each other (headway); the more tightly you can safely operate trains, the better
• Speed of trains at any particular time (average speed is most useful, though maximum is flashy)
• Number of actual trains in service at any particular time, and at peak hours
• Number of cars per train, which can be different per-line or at different times of day
• Per-car passenger capacity: number of seats (or standing areas) per car

Headway and train throughput is, in practice, influenced by:

• Station platform layout and scheduling practices
• Grade-separation from automobiles and pedestrian traffic
• Enough tracks to separate service from freight trains and other agencies' passenger trains
• Optimization of track alignment/layout (including sidings) and signaling systems to reduce delays
• Fast acceleration and deceleration times at stations (braking times particularly)
• Boarding/alighting times (level boarding platforms, wide doors, many doors, etc. improve throughput)
• Mechanical necessities, like engine changes for hybrid systems (e.g. Amtrak in Washington DC)
• Weather and general maintenance practices

Ridership is influenced by factors including:

• Train availability/frequency (number of trains per hour through a particular station; more = higher ridership)
• Train on-time reliability (track record of being more on-time = higher ridership)
• Train convenience/usefulness (whether the train goes to useful locations; more useful = higher ridership)
• Train speed (faster = higher ridership)
• Train ticket cost (lower fares = higher ridership)
• Multi-modal transportation options, like bicycle storage
• Miscellaneous amenities and subjective qualities irrelevant to this discussion

...most of which are influenced as far as the rider is concerned in some way by train system capacity, which is in turn influenced by government funding.

Caltrain's Electrification and Modernization project specifically influences the following metrics:

• More service
  • Caltrain will be offering trains at a higher frequency (up to six per hour)
  • This is possible because electric trains are faster and cheaper to operate than diesels, so for the same amount of money spent on staff wages, you can have more service
• Faster travel times (up to 25%)/system reliability
  • Electric trains are lighter than diesel ones, which improves acceleration/deceleration times.
  • Electric trains have fewer mechanical failures than diesels, which improves on-time reliability
  • Positive train control: a better signaling system that will safely allow for better train interactions, such as smaller headways and higher maximum operating speeds (and thus higher average speeds)
• Better... experience?
  • Electric trains are much quieter and have fewer vibrations that diesel trains, making for a more comfortable ride
  • The new trains are pretty good-looking, which does influence ridership (humans are not strictly utilitarian)
  • Electric trains do not spew toxic gases and maybe that is a cool wow factor for some people

I don't know if Caltrain is specifically investing in much longer trains (probably not for now), but they could if they had enough ridership and funding. That would probably necessitate longer station platforms for optimal operations; ideally passengers can get on or off from any car rather than just a few. My impression is that Caltrain Electrification does not involve dramatic changes to the interior layouts of cars or the number of cars per train, or else I think that would have been expressed more clearly in marketing materials.

In general, few American transit agencies truly operate at maximum potential. I do not think that Caltrain is anywhere near hard capacity. Even established electrical train systems like Philadelphia's SEPTA run at much lower throughputs than European equivalents that have similar track configurations in stations.