A Compromise Proposal for TJPA and CHSRA

by Rafael

over the past six months, San Francisco's Transbay Terminal Center (TTC) project has been the topic of numerous posts on both this blog and the Caltrain-HSR compatibility blog (index at the end of this post). So why am I revisiting this wretched topic yet again?

Well, as Henry Kissinger once famously paraphrased Sayre's Law: "The reason academic politics are so bitter is that so little is at stake." Right now, there's a $400 million grant application from the Transbay Joint Powers Authority (TJPA) to the Federal Railroad Authority (FRA) at stake and, CHSRA is about to ask for $1.28 billion of its own just for the SF-San Jose segment. In addition, the state of California plus several Bay Area counties plus the city of SF are positioned to commit substantial funds of their own on behalf of taxpayers. This dispute is no longer academic, so somehow TJPA and CHSRA need to come up with a face-saving compromise. However, that's no reason to lock in every poor single poor decision each authority has made in this context to date.

My objective is to summarize the problems and, to suggest a variation that may be palatable to all sides (see map at end of post). I doubt this post will actually make a blind bit of difference either way in FRA's decisions on the respective grant applications. However, having stirred the pot vigorously, including off-line contacts with TJPA by way of a member of its Citizens' Advisory Council (CAC), I'd like to at least make sure I didn't leave this last stone unturned. So please, indulge me.

Note: just in case this isn't clear, all of the alternatives mentioned below are based on underground station facilities and approaches to them. (h/t commenter spence)

TJPA

San Francisco's Transbay Terminal Center was conceived as a joint effort by the city of SF, Alameda county's AC Transit and Caltrain to achieve two objectives:

1. to extend the financial district into an area of urban blight south of Mission and,
   
2. to relieve rush-hour congestion at the downtown BART stations (Montgomery and especially, Embarcadero)

The site selected to achieve this is the city-owned Transbay Terminal located roughly at Minna, 1st, Fremont and Natoma Streets. Completed in 1939, the structure was initially served by trolleys running on the lower deck of the Bay Bridge, hence the generous grade-separated access ramps now used by buses. The building isn't worth renovating as it doesn't meet modern seismic code but the ramps do.

To its credit, the city of SF set out to redevelop the entire area with transit access in mind to avoid increasing congestion on both the bridge and city streets. Land near the terminal that is currently used for at-grade parking lots is to be converted to multi-story buildings, a combination of office towers and affordable apartments.

San Francisco voters approved this concept 7:3 via SF city prop H(1999):

SECTION 2. As part of the extension of Caltrain downtown, a new or rebuilt terminal shall be constructed on the present site of the Transbay Transit Terminal serving Caltrain, regional and intercity bus lines, MUNI, and high speed rail, and having a convenient connection to BART and MUNI Metro. Said terminal shall be so designed and constructed as to:

(a) yield the highest possible transit use by residents and commuters;
(b) afford senior citizens, persons with disabilities, and other commuters with the most convenient connections between regional bus lines, MUNI, Caltrain, and BART;
(c) produce the highest density of foot traffic, in conjunction with foot traffic from the Caltrain station, to accommodate mixed use retail development;
[...]
(e) result in the lowest feasible combined costs for construction of the bus terminal and the Caltrain station, without sacrificing the aesthetic qualities of the terminal and station and their interface with surrounding development.

SECTION 3. [...] electrification of the Caltrain line from San Francisco to San Jose prior to or concurrent with the extension of Caltrain downtown [...] tunnel boring techniques [...]

The legal basis for the TTC project therefore requires construction of both a downtown train station for Caltrain and a transbay bus terminal for the benefit of city residents and commuters. The DTX tunnel and train station are neither optional nor were they an afterthought. Note the requirement for the "most convenient" and ADA-compliant pedestrian connectivity between Caltrain and BART/SF Muni subway in the downtown area.

Prop H also mandates Caltrain electrification prior to start of operations and a tunnel that is bored rather than excavated from above via cut-and-cover. The tunnel and railway station infrastructure were subsequently mapped to a second phase of the project because at San Jose's insistence, Santa Clara county refused to commit its share of the electrification funding in light of the sky-high cost of extending BART to Santa Clara. Section 3 explicitly rules out partial electrification, so SF could not proceed until CHSRA offered to come to the rescue. Shoot foot, reload.

TJPA interpreted point 2(c) to mean that the downtown train station would have to be physically underneath the bus terminal to maximize foot traffic and hence, lease revenue from a co-located shopping mall that is supposed to help pay for the project. Amazingly, it also believes this configuration will result in the lowest total construction cost (cp. point 2(e)), even though every tunnel curve excavated under existing buildings is extremely expensive. Shoot other foot.

The option of constructing tracks under nearby Beale Street to create a station that would be intermodal with both the bus terminal and with Embarcadero BART at Market Street was rejected for the following reasons: tunneling risk near the Bay Bridge anchorage, limited width that would require a multi-story station and, potential problems with box sewers under Embarcadero and Mission plus the foundations of older buildings between Market and Mission. There is also a desire to reserve Mission Street for a second BART line served by a second transbay tube, a very expensive project that may one day become indispensable.

An underground station under Main Street (best viewed in satellite mode, zoom in for details of track layout) and land just west of it would permit up to 11 staggered tracks in a single level, seven of them full length (1320'). Afaik, this was never studied, perhaps because it wouldn't generate enough foot traffic for the aforementioned retail outlets. It's all about the shopping, getting from A to B be damned.

The upshot of all this is that the design now features a "train box" with just six platform tracks parallel to Mission Street. The western end of all six lies roughly at the western end of the existing terminal building. In an effort to minimize tunneling cost, TJPA selected an approach via Townsend and 2nd rather than 3rd - let alone one via 7th and Minna or a station under Mission Street. The result is a sequence of three extremely tight curves in the final approach into the train box.



Note that the northern four tracks have since been extended to Main Street at CHSRA's request. The very expensive excavated tail tracks were moved to the southernmost tracks, which are nominally reserved for Caltrain. Harmonizing platform height to the level required for HSR would eliminate hard platform track assignments and hence, the need for tail tracks.

While trains can get around tight curves, this is not at all recommended if their axles are rigid. TJPA cites the example of the main station in Cologne (Germany) whose throat features a minimum curve radius of 550 feet. Please turn up the volume and watch the video below to get a sense of what wheel squeal on the top of the rail sounds like in the real world. Nails on a blackboard have nothing on this. In the TTC, the sound will be even more painful to passenger's ears as the acoustically hard surfaces of a tunnel and underground station tend to concentrate sound volume. The associated wear and tear on both wheels and rails also tends to increase rail/wheel noise emissions all down the line and/or maintenance overheads.



The curve at Townsend and 2nd is similarly tight and, TJPA's engineers and consultants have talked it into needlessly using only straight switches and constructing not two but three tunnel tracks all the way to 4th & Townsend. This forced the use of slow, labor-intensive sequential excavation over a conventional two-track tunnel boring machine.

Separately, Clem Tillier has pointed out problems with the configuration of support columns, including those on the platform tracks which may impede pedestrian flow to and from the island platforms. He has also lamented the lack of architectural grandeur below the surface, imposed by the inclusion of a full concourse level. He cites the interior of Berlin's Central Station as an example of what billions of dollars can buy you.

Note that TJPA claims the orientation of the train box retains the option of one day running trains to the East Bay via a transbay link for standard gauge services. This is not rquired by prop H(1999) and a bit of a crock, at least for HSR, if only because tunneling under the tall buildings between Main and Embarcadero would be prohibitively expensive. More to the point, there is zero room for dedicated HSR tracks between Oakland and Benicia. For the moment at least, there's insufficient demand for single-seat standard-speed service between SF and Sacramento to justify the construction of a fixed link for standard gauge tracks. For the price of just that, you could finance a ton of improvements to Amtrak CC, including bypass tracks and tilt trains for express service between Emeryville and Sacramento.

Summary of legitimate complaints against TJPA:

• failure to anticipate that the catchment area of the SF HSR station spans multiple counties, meaning that high ridership depends critically on excellent connections to all existing high-capacity rail transit systems
  
• failure to commit to an ADA-compliant pedestrian passage to BART/SF Muni
  
• loud wheel squeal (and associated wear and tear) due to three tight curves
  
• extremely long station throat (= low throughput)
  
• extremely expensive three-track tunnel to compensate (= stupendous cost)
  
• poor aesthetics of and possibly poor pedestrian flow to and from platform level
  
• doubtful claim of option for future standard-gauge fixed link to East Bay

CHSRA

One reason there is now such tension between TJPA and CHSRA is that that latter agency was hamstrung by a four-year delay in getting prop 1A(2008) onto the ballot, compounded by a year spent on a starvation budget imposed by Gov. Schwarzenegger who was dissatisfied with the lack of private investors in the funding plan. Since he who pays the piper calls the tune, this massively weakened CHSRA's leverage in negotiations with TJPA while it was making decisions on the underground portions of the project.

In particular, CHSRA failed to insist on an underground pedestrian tunnel all the way to a BART/SF Muni subway/streetcar station, even though HSR ridership will depend heavily on excellent connection to these existing high-capacity rail services and prop H(1999) actually requires something along these lines. Forcing many thousands of passengers to hoof it across busy city streets every day is not an acceptable outcome for a multi-billion dollar project.

For order-of-magnitude reference, BART delivers about 60,000 transbay passenger trips on a normal weekday Labor Day weekend Monday (more on regular weekdays, h/t commenter mike), AC Transit buses just 12,000. GG Transit buses come in at around 9,000 and GG Ferries at a surprisingly high 6,000. SF Muni metro and the F streetcar line deliver 170,000 trips per day, about half the number of all of BART.

One reason CHSRA may have been reluctant to kick up a fuss years ago is this telling assertion in the Bay Area to Central Valley Final Program EIS/EIR (chapter 8, pp20 PDF):

The capital costs needed for the HST component of the Transbay Transit Center (including the 1.3-mile extension) is estimated to be similar to the estimated costs for the 4th and King option. Since the rail component would be shared with Caltrain services, the Transbay Joint Powers Authority funding plan assigns only a portion of the rail related Transbay Transit costs to the HST system.

As if an HSR station at 4th & King wouldn't be shared with Caltrain! Given that facility is at grade and has 12 platform tracks, CHSRA evidently believed at the time that the HSR project's share of the cost of the anyhow-planned DTX tunnel and train box would be quite small, but it failed to get that in writing from TJPA. Now, the forecast for the underground portion is on the order of $2.8 billion and TJPA wants the HSR project to fund the lion's share of that on top of Caltrain electrification. Section 2704.04(2) of AB3034 turned CHSRA's preference for the TTC into a hard mandate. Shoot foot, reload.

CHSRA is also locked into the idea that San Francisco is the end point of a train trip from Southern California. It insists on dwell times of 30-40 minutes in the TTC, even though AB3034 mandates feasible headways of no more than 5 minutes for the entire HSR network. With just four platform tracks at the TTC, dwell times above 20 minutes - including the time needed to traverse the throat twice - are out of compliance. Unfortunately, instead of trying to bring down dwell times, CHSRA is now looking for ways to secure more platform tracks in SF. AB3034 limits the network to 24 stations and 4th & King is too far from downtown for anyone to argue with a straight face that it could somehow be considered part of a modified TTC design. A relatively cheap tunnel + station with four straight full-length platform tracks, intermodal with Civic Center BART/SF Muni, with an option for four more under 8th (h/t to commenter Andrew), is now also out of the question for HSR.

Worse, since TJPA already has a Record of Decision on its design, any major changes at all would jeopardize its grant application against the $8 billion HSR portion of ARRA and invite the wrath of an entire city. Shoot other foot.

Ergo, CHSRA should get cracking on reducing dwell times to below 20 minutes so it can make do with four full-length platforms. One way to achieve that is to redefine the route of any given train as SoCal to SF and back again. This would preclude cleaning and light housekeeping of the seating areas in SF, but then Amtrak doesn't do that nor reprovision the cafe cars every 400 miles, either. The restrooms could be cleaned one-by-one en route in the SJ-SF-SJ segment. Cleaning staff could use Caltrain to commute if required. A little lateral thinking by CHSRA would go a very long way here.

Summary of legitimate complaints against CHSRA (in this narrow context):

• incorrect/naive assessment of cost exposure to TTC project during HSR program-level EIS/EIR process
  
• failure to analyze any alternatives to create a single Central Railway station served by HSR, Caltrain, BART, SF Muni subway and SF Muni streetcars
  
• inefficient operations concept, leading to excessive dwell times and need for more platforms than TJPA could reasonably make available while still meeting its commitment to Caltrain under prop H(1999)
  
• failure to focus technical complaints on genuine design flaws
  
• failure to raise the alarm early enough

Compromise Proposal

For better or worse, the political reality is that CHSRA's chances of getting TJPA to abandon its train box under the bus terminal are now slim to none. In part, that's a result of Gov. Schwarzenegger's actions but there's plenty of blame to go around.

A reasonable approach might look as follows:

1. Accept that at least some HSR trains are going to have to use the TTC train box, warts and all. In the early years of operations, make that 100% of HSR trains. Change operations concept to reduce dwell times in SF to below 20 minutes and ensure compliance with the 5 minute headway requirement in AB3034.
   
   
2. Get the city of SF to commit to a second, separate EIS/EIR for constructing a dedicated underground pedestrian passage between Embarcadero BART/SF Muni and the HSR tracks under Main Beale Street (this was already studied in 2007 but remains unfunded). Design it complete with bright lighting, moving walkways and security staff, to actually implement the spirit of section 2(b) of prop H(1999). In addition to connecting to the concourse level, consider also connecting to the BART island platform from below to address existing pedestrian flow constraints there. Those will only get worse as the financial district expands south of Mission. Start of operations would have to be concurrent with that of the TTC train box.
   
   
3. Consider using Talgo equipment, since that is the only manufacturer to offer both double-deck commuter and suitable high-speed trains with very short cars, individual axles for each wheel and passive steering of each wheelset. That means they can negotiate very tight corners with reduced squealing (the tractor cars still have conventional rigid axles). If other trains vendors are chosen, prioritize the development of dry lubricant strategies that are compatible with EMU traction and don't reduce line capacity by increasing emergency braking distances. Apparently, that's a non-trivial problem or Deutsche Bahn would be using such a system in Cologne today. What's available on the market may be suitable for coasting through at speed, but in a station throat braking and acceleration are required.
   
   Note that TJPA has no authority to de facto make train vendor decision for Caltrain and/or CHSRA, nor should it. All I'm saying is that as long as the three curves in the approach remain this tight, Caltrain and CHSRA will have no choice but to somehow mitigate the inevitable consequences. If the aural experience of the SF train station is negative, ridership will suffer.
   
   
4. Consider harmonizing the platform height of Caltrain locals at HSR levels and assigning platform tracks on real-world demand, eliminating the need for tail tracks. Optionally, extend the southernmost platform tracks (#21+22) as far as Main Street as well.
   
   
5. Irrespective of platform height harmonization, consider letting Caltrain run strictly regional HSR trains between SF and SJ as long as there is spare capacity on the HSR tracks in the SF peninsula.
   
   
6. Eliminate the 4th & Townsend station from the DTX tunnel. Instead, have tracks descend at 3.5% gradient immediately after crossing Mission Creek through the curve near 7th & Townsend. Use switches to create an underground station with two short platform and two through tracks on 4th & King property. If absolutely necessary, stack additional platform tracks on top of those.
   
   
7. Limit tunnel to two tracks between 4th & Townsend to 2nd & Folsom and use a single TBM to excavate that. Deploy crossover switches in the last section, followed by two Y plus one reverse Y switches to branch into three platform connector tracks. Just north of Tehama, use switches and diamonds to implement turnoffs toward the TTC train box. Dead-end the through tracks for now.
   
   
8. Negotiate HSR and Caltrain ridership conditions that would require the city of SF to kick off a third phase of the TTC project, subject to a third EIS/EIR process. This would implement an "auxiliary terminal" featuring three additional full-length platform tracks at level -2 under 2nd Street between Market and just south of Howard. This would be intermodal with the existing Montgomery BART/SF Muni at Market plus city and GG transit buses at 2nd/Mission and also permit a future second BART line along Mission at level -3. Note that the available width under 2nd, including sidewalks, is 75 feet.
   
   A second pedestrian connector passage, similar to the first but above e.g. Minna Street between 1st and 2nd, would be included in the scope of the EIS/EIR auxiliary terminal.
   
   
9. The auxiliary terminal concept would be considered part of the TTC but remain unfunded for the time being. Let's see Caltrain and HSR actually achieve something approaching their rosy ridership forecasts first.

View Aux Terminal under 2nd in a larger map

NOTE: I've edited the map to move the phase 2 pedestrian passage from Main to Beale Street since TJPA already studied that alignment in April 2007. It has languished for lack of $105 million in funding, something the HSR project can and IMHO should help provide if it ends up using TJPA's TTC train box as designed.

---

Links to previous posts related to the Transbay Terminal on this blog:

Sep 21 CHSRA Staff Recommendation on Phase 2 Stimulus Funding
Sep 18 Deputy AG Letter Supports CHSRA's Transbay Position
Sep 16 What's Up With The Transbay Terminal/
Aug 25 California Applies For $1.1 Billion In HSR Stimulus Funds
Jun 06 SJ, SF Mayors Push Transbay, Diridon, Caltrain Upgrades
Apr 29 New Transbay Terminal Renderings
Apr 14 Quentin Kopp on Transbay Terminal
Apr 05 Transbay Terminal Redux
Mar 24 BruceMcF On Transbay Terminal
Mar 14 Your Weekend Transbay Terminal Update
Mar 03 Tight Squeeze At Transbay Terminal?

On Clem Tillier's excellent Caltrain-HSR Compatibility Blog:

Sep 19 Platform Height
Jun 13 Future Transbay
Jun 06 Build Me A Train Box
Mar 25 Focus On: SF Transbay Transit Center

Deputy AG Letter Supports CHSRA's Transbay Position

Yesterday the California Attorney General's office responded to an August 21 letter from the Transbay Joint Powers Authority. The TJPA letter argued that it is "legally improper" for the CHSRA to study any alternatives to the Transbay Terminal as the San Francisco terminus. Deputy AG Christine Sproul, writing on behalf of AG Jerry Brown, explained the AG office's position that CHSRA is entirely correct to study other alternatives. The letter is reproduced below:

Deputy AG Transbay Letter to CHSRA ED 91709

I have to run and catch a train here in Sacramento, but I wanted to get this up there for everyone on the blog to read and react to. Obviously this means the dispute between CHSRA and TJPA is not going away anytime soon. I continue to believe that political leadership, particularly from San Francisco's powerful federal representatives, is desperately needed to bring CHSRA and TJPA to the table to develop a workable solution.

The Vexed DTX Tunnel

Just a techie tidbit note today regarding the DTX tunnel that is at the heart of the engineering side of the dispute between CHSRA and TJPA on whether the current design meets CHSRA's future needs. I know we've been over this too many times already, but somehow the issue needs to be put to bed such that everyone can save face and focus on maximizing California's share of the $9.5 billion in federal dollars already on the table. Protracted tiffs don't do much for the confidence of the general public, let alone potential private investors, in either TJPA or CHSRA.

My objective for this post is to suggest a tunnel sharing and operations timetable strategy that might help bridge the gap. First, a quick recap of the saga so far.

Issues Related to Planning and Funding

TJPA has been planning the entire Transbay Terminal since SF voters approved prop H in 1999, with the objective of bringing not just Caltrain but eventually also HSR under the same roof as a large number of bus services. The old building dates to 1939, has seen better days and is anyhow no longer up to seismic code. The only part that will be re-used are the bus ramps that once allowed electric trolley cars to run across the lower deck of the Bay Bridge. The underutilized neighborhood south of the new building will also be redeveloped.

The DTX tunnel is the bit between Caltrain's existing terminus at 4th & King Street and the basement of the new terminal building. As designed, it features three tracks under Townsend and 2nd Streets and widens into a curved throat section to reach six platforms tracks accessed via an underground concourse level and three full-length wide island platforms. Of these, two will feature the level boarding height to be chosen by CHSRA and the other the one chosen by Caltrain. The outside tunnel tracks are to be shared by both services and are permanent as inbound and outbound tracks, respectively. The center track will apparently alternate between inbound and outbound traffic.

CHSRA has recently raised a red flag regarding the design, claiming it couldn't support the 12 HSR trains per hour (tph, meaning that number each way) during peak periods claimed in the most recent ridership forecast for 2030. There seems to be fairly broad agreement among the readership of this blog that this is a new and excessive demand made public only after TJPA decided to bypass CHSRA in seeking a slice of the HSR dollars in the recent stimulus bill. Quentin Kopp is concerned this would set a precedent and cause CHSRA to lose control of project cost.

TJPA claims its plans are based on a previous estimate of just 4tph and a minimum dwell time of a full hour. The latter is itself a highly questionable requirement, given that terminal stations in Europe manage to turn HSR trains around in 6-10 minutes. They are treated as through stations that happen to require trains to reverse direction, generally with a change of driver. Old-fashioned terminus stations are grand buildings providing small town folk with access to a metropolis, reached after many hours or even days on the move. Thanks to high speed, even San Diego-SF-San Diego will amount to just a single eight-hour shift for employees, so in that sense SF could indeed be considered a through station along out-and-back routes originating in SoCal and Sacramento.

The Authority would be on much firmer ground if it stuck to AB3034, which point blank requires that the entire network must support headways of no less than 5 minutes. This refers to the time interval between the nose of one train and the next one running in the same direction on the same track. The technically required minimum is a function of speed and emergency braking distance at that speed. For moderate speeds, experienced operators of modern train control infrastructure can make do with as little as 2.5 minutes, so the legal target set by the bill is conservative. As will become evident shortly, the link between short headway capability and system throughput is not always straightforward.

Technical Issues and Solution Concepts

The beef that Clem/Richard Mlynarik, BruceMcF and yours truly have with the current design of the DTX tunnel is twofold:

a) at just 500 feet, the two curves in the tunnel will prevent at least the HSR trains from running them at much more than bicycle speed. In addition, we expect screeching noises as the long wheelbase trucks needed for high speed stability are dragged kicking and screaming around the corner. Passengers on board and especially, anyone present on the platforms would hear a sound reminiscent of fingernails on a blackboard, just much louder. Special lubricants might help keep both the noise and the wear and tear down, but no brand-new design should need them. The radii are also too tight for off-the-shelf Japanese shinkansen designs, which need ~925 feet. Even for European designs, 500 is the number the marketing department made the engineers sign up to, not one they'd recommend for brand-new track.

b) the slow speeds combined with the tunnel layout combined with train lengths of 660-1320 feet mean that during peak periods, inbound and outbound trains of both operators will block each others' paths to such an extent that the "throat" between the tunnel proper and the platform tracks becomes the throughput bottleneck. It's highly unlikely that HSR could achieve 5 minute headways during Caltrain's rush hour with that design.

Both post authors and commenters have propsed a wide range of solution concepts on both this blog and Clem's. Here's a recap:

• terminating some or all HSR trains at 4th & King
  
• a central rail station at Market & 7th instead of the Transbay Terminal
  
• redefining the Transbay Terminal to include a narrow two-level heavy rail station under Mission Street, reached via a short underground pedestrian passage and featuring moving walkways along the 1/2 mile concourse level
  
• keeping the tracks in the basement, but redesigning the DTX tunnel as a one-way single-track loop through the building from east to west; any future second transbay link would then be BART down Mission Street
  
• redesigning it to run up 3rd Street to increase curve radius for just two - possibly individual track - tunnels
  
• minimally, some tweaking of the curve radii and the use of curved switches in the throat of the official three-track tunnel design
  

Dedicated Single Tunnel Tracks

In the vein of this last concept, I'd like to add one more suggestion to the list. Since HSR and Caltrain are supposed to get dedicated platforms and platform tracks anyhow, I figured why not give each of them a single, dedicated track in the DTX tunnel as well. That would at least get the operators out of each others' hair. A third track should be avoided to keep the tunnel engineering as straightforward as possible so the curve radii can be increased without breaking the bank.

The idea is really quite simple: each operator sets the signals in the tunnel track to outbound and runs a group trains out in quick succession. The timetable is arranged such that an equal number of inbound trains arrives at the mouth of the tunnel just as the last of the outbound trains clears it. The operator sets the signals in the opposite direction, the platforms tracks fill up again and the process repeats.

The advantage is that as long as traffic is guaranteed to be one-way, headways as small as three minutes are quite realistic. No outbound trains blocks any inbound one, no HSR train any Caltrain and vice versa. In other words, there is no throat in the classic sense, just two independent tunnel tracks that fan out to two resp. four platform tracks that are alternately used in one direction or the other for a well-defined period of time.

The disadvantage is that each operator's timetable would feature a number of trains in quick succession, followed by a period without service in that direction. Note that in each of these groups of trains, the fastest service classes (e.g. express) come first, followed by the slower ones (e.g. semi-express). This ensures headways do not decrease below three minutes in nominal operations. For two consecutive trains of a slower class, it may go back and forth from the minimum value to a higher one.

Spreadsheet Model

To get a better sense of the kind of timetable this would produce, I made a number of assumptions and plugged them into a spreadsheet. In addition to the three-minute headways, I assumed that the cumulative delay for an outbound group of trains would be no more than one minute. For inbound groups, I allowed a three-minute buffer and assumed a two-minute dwell time for trains making a stop between San Jose and SF. Finally, I assumed Caltrain's commuter EMU equipment would traverse the 1.3mi tunnel in two minutes (39mph average speed thanks to high acceleration and short wheelbase trucks), whereas HSR trains would take three (26mph average).

For service patterns based on half-length trains (660ft or less), the first inbound train would proceed to the end of the platform track. The second would stop before colliding with the first. However, since it's a terminal station, the later arrival would have to be the first one to leave, resulting in uneven dwell times. Also, I assumed a platform track would be cleared entirely before trains from the next inbound batch are admitted. This is how an operator would use the facility during rush hour. At off-peak periods, the ends of the platform tracks can be used for parking.

The results were as follows:

• For HSR service based entirely on single trainsets, I assumed a group size of four trains occupying one track on each island platform. The first two were express, the second two semi-express trains on the SJ-SF segment. This affects the length of time the track needs to be reserved for inbound traffic. Note that I did not consider service class impacts south of San Jose for this preliminary analysis. Instead, I assumed appropriate service groups would be created via wait states in San Jose.
  
  After allowing four trains to leave, four new inbound ones would be admitted, followed by the other four trains still in the station and four inbound ones to replace them. The period for this pattern of 8 trains each way works out to exactly 60 minutes, i.e. 8 tph. The minimum dwell times for the trains in each group worked out to 38, 44, 36 and 42 minutes, respectively. Because of the buffers built into the schedule, they could be up to four minutes longer.
  
  
• I also looked at HSR service based exclusively on full-length trains. With a group size of four, this also works out to 8 tph - but each of train would now have twice as many seats! The snag is that the minimum dwell times are down to just 11, 11, 9 and 9 minutes, respectively. As discussed above, that is considered enough for a terminal in Europe. However, if a large fraction of seats is actually occupied in SF, seat reservations and some pedestrian flow control would be highly advisable to avoid delays. Evidently, trainset utilization rates are much higher if full-length trains are used. Note that it's very easy to couple and uncouple HSR trainsets at stations, so operators could transparently switch to single trainsets during off-peak hours.
  
  
• HSR service based on full-length trains and a group size of just two yielded a throughput capacity of 7.06 tph, with minimum dwell times of 21 minutes.
  
  
• Separately, I looked at Caltrain local service based on 8-car trains that would be used during rush hour. With a train group size of four, throughput worked out to a very respectable 9.23 tph. Minimum dwell times were 6, 12, 6 and 12 minutes, respectively.
  

Fiddling with the parameters, it quickly became apparent that the minimum headway had the greatest effect on throughput, followed by the time required to traverse the DTX tunnel, dwell time at through stations down the line. Doubling the cumulative buffer period allowed for inbound Caltrain groups from 3 to 6 minutes resulted in a loss of only 1 tph in throughput.

Overnight Parking

Note that CHSRA still needs a solution for overnight parking of additional trainsets, as the first ones of the day will take some time to arrive from Merced and LA. The old Brisbane yard near Bayshore Caltrain would do nicely and could double as a transshipment center for High Speed Cargo trainsets that ride piggyback on single passenger trainsets during off-peak hours. Toward the end of the day, selected passenger trains would terminate at Millbrae/SFO.

Conclusion

Provided that inbound trains are grouped neatly and operators are willing to accept that consecutive trains in the same direction may run anywhere from 3 minutes to 13, 17 or even 21 minutes apart, aggregate throughput of over 17 tph is possible with this concept. For reference, a single loop track serving all six platforms with a minimum headway of 3 minutes would support 20 tph and provide more flexibility if CHSRA and Caltrain decide on a common platform height after all.

Cost Containment Opportunity

Just for kicks, I also looked at the possibility of saving some money in phase I by extending the dedicated single track for HSR beyond 4th & King to Bayshore. Caltrain already has four short tunnels in that stretch, CHSRA intends to bore new single track tunnels to either side of that. The CHSRA web site gives a time of 13 minutes for Transbay Terminal to Millbrae/SFO, so I figured it would take about 9 out to Bayshore. This longer single-track section caused HSR throughput to decrease from from 8 to 5.71 tph (4.14 tph for full-length trains with a group size of two but minimum dwell times of 33 minutes). For the single-trainset scenario with a group size of 4, minimum dwell times went up by 12 minutes. For full-length trains with the same group size and throughput number, they were unchanged.

In other words, it would be possible to shift some tunneling overheads south of 4th & King from phase I to phase II of the overall bullet train project, given that 4.14-5.71 tph will be enough for HSR operations for a while. Note that running northbound HSR trains east of Caltrain in that section would currently force UPRR trains to cross the HSR track. By the time HSR needs dual tracks between Bayshore and 4th & King, it's entirely possible the mighty Port of SF will no longer be served by UPRR's South City Switcher - a freight train running in streetcar mode.