Uncrooking San Francisco's Crookedest Tunnel

How do we figure out the best way Caltrain and HSR get to the Transbay Center?
Tearing down a freeway?
Rerouting a planned train tunnel that's already EIR certified?
Build housing and offices on a relocated rail yard?

Crazy? Not really considering there's not enough money for the tunnel.

When the Mayor's Office suggested "Let's be San Francisco and Take Down the Freeway", the earth shifted a bit, but we're used to that in quake prone SF. The proposal calls for tearing down I-280 north of 16th Street and converting the 30 acre Caltrain railyard and (and some freeway land) into a mixed use neighborhood.  At an estimated worth of $228 million, some of that money could help fund the $2.5 billion construction of the downtown extension tunnel (DTX).

Additional Posts on the Caltrain Downtown Extension and the Railyard Redevelopment
Caltrain Railyard Hide and Seek - a look at where to relocate the railyard if the 4th & King yard is redeveloped
(Ped) Tunnel Vision - a look at the pedestrian tunnel options to link the Transbay Center with BART and Muni Metro on Market Street
Poll: Where should BART go in SoMa? - a look at possible alignments from a 2nd Transbay Tube through SoMa and on to Geary Street. Regarding Caltrain, how would a 2nd Transbay Tube best serve Caltrain to the East Bay, and how would two new tunnels with stations in SoMa best serve San Francisco and the region?

Another component of the "Let's be San Francisco" presentation, was considering rerouting the rail tunnel to the Transbay Center. The Caltrain Downtown Rail Extension (DTX) calls for tunneling from the current Caltrain Railyard up to the Transbay Terminal and taking three sharp turns that will dramatically slow trains, increasing travel times and reducing tunnel capacity. Rerouting the DTX tunnel could straighten out much of the tunnel, and improve travel times and capacity.  Might rerouting the DTX tunnel down Mission Street to parallel BART and Muni on Market Street with a new station connecting to Powell or Civic Center create a grand opportunity that makes for a better rail system and fosters more economic opportunity, all while improving the tunnel and coming at no greater cost?

Read on to learn more about the options and see larger versions.

The Challenges
Are these ideas crazy? Ill advised? Misguided? Financially impractical?  Not really considering there's not enough money for the tunnel and there are many other challenges with the current plans to have rail reach the Transbay Transit Center. The current Caltrain DTX and Transbay Transit Center plan has great promise and does many things right. However, there are four critical challenges with the current design.
  1. The 16th Street crossing conflicts: rail, street, freeway, buses, pedestrian and bike don’t mix well under many plans
  2.  Rail capacity is limited due to the I-280 pillars
  3.  The three sharp turns in the DTX tunnel limit speed and capacity
  4.  The tunnel and entire DTX project is currently underfunded and would only receive needed funding by 2022 or later. 
I’ll be going into all the issues related to getting rail to the Transbay Center over several posts. This post will focus on the DTX alignment and alternatives.
Image: Troy Holden via Streetsblog SF

The Current DTX Plan

The current plan calls for Caltrain and HSR trains to travel along the existing rail right of way between the northern Potrero Hill Tunnel portal at Mariposa Street up to the Caltrain railyard between Townsend and King Streets. The DTX plan would have trains take three 90 degree turns before reaching the Transbay Center:
  • Turn east 7th & Townsend in a trench
  • Turn north at Townsend and 2nd Street in a tunnel
  • Turn east at 2nd Street and Howard in a tunnel
That seems like a lot of turns, especially if they have to travel at the speed of a bicycle. Trains would decend into a tunnel beginning at 6th Street and Townsend. An underground Caltrain station at 4th and Townsend would add to the existing Caltrain terminal station at 4th & King. 

Without sufficient funding for the tunnel, we're at a point where it would be prudent to reevaluate the cost, funding and route of the planned DTX. By increasing land value, both tearing down I-280 and relocating the yards could generate more revenue to help fund the project. Could realigning the tunnel and adding a station do the same? Changing the alignment would be an uphill battle to put it mildly. With environmental work finished and engineering planning underway, changing the alignment would cost extra money to conduct a new environmental study and begin new engineering plans.

Even so, maybe one of the alternative routes could prove to be a cheaper tunnel, or generate more funds, or create new connections with other rail systems that would gain support and funding from other groups. 

Following are maps of the current plan and 4 new alternative alignments, 2 of which were presented by SFCTA. Each alignment has a designated "name" and also referenced by the streets they follow. The names are based on historic elements in the area such as old geographic points (e.g. Steamboat Point at Brannan and 2nd), or actual old street names (6th Street was once called "Simmons Street"). I've named the current planned DTX alignment the "Steamboat Rincon" alignment that follows Townsend and 2nd streets because it passes through the historic Steamboat Point and Rincon Hill.

I looked up the EIR document to see what alignments were originally considered for DTX. As the map shows below, all of them effectively went from 4th and King to the Transbay Center via 2nd, 3rd, Essex, First or Beale streets. None of them considered starting the tunnel earlier or connecting to other transit systems at multiple points.
Whatever tunnel and stations get built, we should be considering what we're asking for and what's most important. Simply stating this is a tunnel to get to the Transbay Center is missing the point. We're creating a valuable piece of infrastructure that should work for at least a century into the future and work for not just Caltrain, HSR, and downtown, but benefit the entire region, including other transit operators, residents and commuters. Below is a list of goals that each tunnel alignment and station location can be measured against.

Goals for Caltrain DTX and station locations

  • Provide reliable, efficient, and comfortable train service (local, regional and intrastate) from San Francisco that serves residents, commuters, travelers, and shoppers
  • Link Downtown San Francisco to the region and state via train (1st to the Peninsula, later to rest of region)
  • Create a rail alignment and train stations that will beneficially serve as much of San Francisco's transit and intercity train needs as possible, but within an achievable cost.
  • Create rail stations (Transbay Center and others) that can best link to other transit systems in the city and the region
  • Create rail stations (Transbay Center and others) that are in close proximity to dense employment centers and dense housing
  • Ensure that each station has high pedestrian connectivity from all directions, that are safe, and attractive to use. Ensure safe and attractive bicycle connectivity as well.
  • Create stations and rail alignments that will be best positioned to link and support with future rail transit (2nd Transbay Tube for BART, 2nd Transbay Tube for HSR, BART to Richmond, etc.)

  • The Solutions

    Rerouting the DTX route and tunnels would greatly improve travel times and rail capacity (due to not having slow trains clogging up the tunnel). Several alternatives considered during an San Francisco County Transportation Authority (TA) design charrette were presented by the Mayor’s Office.

    East Route
    • Tunnel via 4th Street through Mission Bay and on to the 2nd Street Tunnel already planned. The Mission Bay Station is moved 1-2 blocks west to 3rd or 2nd & King.
    West Route
    • Tunnel via 7th Street alongside Mission Bay and arcing through SoMa north of Townsend to the Transbay Center. A Mission Bay Station could exist at a spur to 4th & King, or somewhere along 7th St south of Townsend. 
    Although these are only preliminary alignment considerations, they are filled with opportunities and some challenges, much like the current DTX planned alignment. Before going into the details of the options I want to highlight how solutions to problems are found, and sometimes found with limitations.

    Often when searching for a solution to a problem, the solutions envisioned only address the problem at hand. However, they don't always look at the margins and into the bigger picture, the less obvious or less conventional solutions. Removing I-280 and developing the railyards are a great example. When DTX and the Transbay Center project was planned, never were these two ideas presented over the early years of planning. However, we now see that doing both will not just address funding and street crossing challenges, but also reconnect three neighborhoods (Mission Bay, Potrero Hill, and SoMa) and make for a better place to live, work and play and thus a better city.
    Image: CaHSRA via GreenCaltrain.com
    Readdressing the rail tunnel alignment could create similar global solutions never imagined when only looking to get rail to the Transbay Terminal from the Caltrain Yards.

    The Rail Alignment Options

    As mentioned earlier, the TA and Mayor’s office presented 2 alternatives to the Planned DTX alternative. Both of them considered having a Mission Bay station, but no additional stations, say at 16th Street, or in SoMa, where employment growth continues.
    Image: SF Gate, Razing I-280

    Why not route the tunnel so that it could benefit, not just Caltrain, HSR and the existing stations (4th & King, Transbay), but also promote regional transit with transfers to other modes like BART, Muni Metro, and Muni buses. Similarly, alternatives compatible with a future Second Transbay Tube (HSR/Caltrain and BART) should be considered. Finally we should explore options that might relieve capacity stress on the BART’s two downtown stations (Montgomery and Embarcadero).

    Read on and take a look at the 5 options considered with analysis of their pros and cons and opportunities.

    The Grand Curve: 7th Street to Transbay

    The Grand Curve is 7% shorter than the planned Steamboat Rincon alignment. Such an alignment could still provide a Mission Bay Station, but on the neighborhood's west side (on 7th St) rather than its north side (on Townsend). A SoMa station is possible, although placing it at Moscone Center may be too close to the Transbay Center to be practical. A pedestrian tunnel should be constructed to link the Transbay Center to Embarcadero or Montgomery BART stations to allow for and encourage transfers between BART and Muni Metro with Caltrain and HSR.

    Pros Cons
    Curves & Tunnel Capacity
    • Large curve from 7th & Townsend to Howard and 4th  
    • No sharp curves  
    • Greatly improved train speeds due to wide curve

    • May require 1 medium curve from Howard to Transbay Center between 3rd and 2nd streets.
    • Mission Bay 7th Street Station. 
    • Potential Moscone Howard Station.

    • Removes  4th & Townsend Station 
    • Moscone Howard may be too close to Transbay Center to be a practical station
    Tunnel Alignments
    • Path goes below private land and buildings. Buildings, including Hall of Justice and Moscone Center could be affected either structurally or by vibrations unless tunnel is sufficiently deep.
    Access Opportunities
    • Access to Mission Bay & Potrero Hill and UCSF. Transfers to 22 Muni BRT
    • Access to Moscone Convention Center and Yerba Buena District
    • Transfers to T-Third at Moscone Station.

    • No direct access to North Misson Bay or South Beach
    • No stations close to AT&T Park.
    Length (19th Street to Transbay Center)
    • 2.2 miles, ~800 feet (-7%) shorter than Townsend 2nd Route
    • New EIR and engineering for the entire route
    • Possibly cheaper construction than planned DTX tunnel due to tunnel boring the entire length.

    • New EIR and engineering for entire route
    • A Moscone Station would add to cost.
    • Removing freeways has a strong track record in San Francisco
    • A Moscone station on Howard may be enticing.

    • Changing tunnel is politically challenging
    • Moscone and other building owners may protest deep tunnel under  them.
    The Grand Curve is not a bad idea. However grand it is, it may just go below too many buildings for those owners. If just a few small (or large) owners banded together, this alignment could fall apart politically.

    Mint Harris: 7th Street to Mission Street

    Linking BART/Muni to Caltrain here allows residents north and east of Civic & Center and Powell to shorten their bus/train ride by up to 10 minutes. This could be a greater savings when traffic on Market Street is factored in. Linking Caltrain at Civic Center/Powell also reduces stress at BART's Montgomery and Embarcadero stations which are virtually at capacity. If the only link between Caltrain and BART is at Embarcadero, then Embarcadero will easily become overcrowded. 

    Creating a station at 6th & Mission gives South Bay and Peninsula commuters better access to the emerging Mid-Market job center as well as Civic Center area. Conversely, commuters from the Richmond, Sunset, and Haight would be able to transfer to Caltrain much earlier, and avoid crowded buses shuffling down Market Street all the way to the Transbay Center. Finally, BART commuters transferring to Caltrain could choose either the crowded Embarcadero or the less crowded Powell Street. We can assume most East Bay BART commuters might transfer at Embarcadero (unless it is still very crowded), but folks coming from the 16th St Mission, 24th St Mission, Glen and Balboa Parks, would transfer at Powell Street to reach Caltrain.

    Although the route is 8% longer, the opportunites created by a Mission 5th Street Station may outweigh the extra length and costs associated with rerouting DTX.
    Pros Cons
    Curves & Tunnel Capacity
    • 1 major curve at 7th & Mission
    • Improved train speeds
    • Mission Bay 7th Street Station between 16th and Mission Bay Blvd. 
    • Mission and 5th Street between 6th & 5th.
    • Removes current 4th & King Caltrain station.
    Tunnel Alignments
    • Follows under streets much of its journey.
    • Path goes below private land and buildings at 7th and Mission, and near Transbay Center. 
    • Possibly goes under Moscone Center.
    Access Opportunities
    • Access to Mission Bay, Design District & Potrero Hill. 
    • Transfers to N-Judah and 22 Muni BRT. 
    • Access to Union Square, Mid-Market & Civic Center. Transfers to T-Third at Union Square Station. 
    • Links to BART & Muni Metro at 2 stations.
    • No access to South Beach. 
    • Railyard development farther from a train station than 4th & Townsend station. 
    • AT&T Park not as close.
    Length (19th Street to Transbay Center)
    • 2.3 miles
    • ~900 feet (+8%) longer than Townsend 2nd Route
    • New EIR and engineering for the entire route
    • Possibly cheaper construction than planned DTX tunnel due to tunnel boring most of the length.
    • New EIR and engineering for the entire route. 
    • Building extra stations (e.g. Mission & 5th St) adds cost.
    • Removing freeways has a strong track record in San Francisco. 
    • A Mid-Market/ Moscone station on Mission may be enticing.
    • Changing tunnel is politically challenging. 
    • Building owners may protest deep tunnel under them.
    This option gets almost everything you could possibly want, save for the need to do an EIR and design of the tunnel.

    Long Bridge: 4th Street to 2nd Street

    This route was proposed at the SFCTA design charrette. Baseball fans will especially like this alignment as it gets fans even closer to the ballpark than the current 4th & King station. The main advantages of this alignment are being the shortest and 13% shorter than the current planned Steamboat Rincon alignment. In addition, this alignment would only require new environmental and engineering work from Brannan Street south - approximately half the tunnel length. 

    The 3rd and King Station could be situated such that the south end is located south of Mission Creek and McCovey Cove, while the north side is at King Street in North Mission Bay.

    Pros Cons
    Curves & Tunnel Capacity
    • 2 major curves at 16th & 4th and 2nd & Howard
    • 1 minor curve at 2nd & Townsend
    • Improved train speeds
    • 1 tight curve at 2nd & Howard entering the Transbay Center.
    • 3rd & King Station
    • Moves current Caltrain station 1 to 2 blocks east. 
    • No additional stations.
    Tunnel Alignments
    • Path remains below street the vast majority of its length.
    • Path goes below private land and buildings at Mission Creek, including AT&T Park.
    Access Opportunities
    • Access to Mission Bay & South Beach.
    • Transfers to T-Third and N-Judah at King Street station. 
    • Close to AT&T Park and Mission Rock development.
    • No access to 16th Street Corridor. 
    • No additional access to BART
    Length (19th Street to Transbay Center)
    • 2.0 miles, ~1500 feet (-13%) shorter than Townsend 2nd Route
    • New EIR and engineering for tunnel south of Brannan
    • Possibly cheaper construction due to 13% shorter tunnel.
    • New EIR and engineering for tunnel south of Brannan.
    • Removing freeways has a strong track record. 
    • Half of the tunnel would not be changed (north of Brannan)
    • Changing tunnel is politically challenging. 
    • AT&T Park and other building owners may protest deep tunnel under them.

    The route roughly follows the "Long Bridge" that once crossed Mission Bay. However, Long Bridge actually follows what is now 3rd Street.

    Simmons Howard: 6th Street to Howard Street

    Although this route has challenges, it could meet most of the needs. Transfers with the Muni T-Third are accomplished at Howard 4th Street station next to Moscone Center. Transfers to BART are accomplished at the Transbay Center. Finally, the new development on the old Caltrain railyards has a station sitting in the middle of the development.

    This option also allows for the Mission Bay Station to straddle Mission Creek, providing access to both sides. The downside of the option is that a Mid-Market BART transfer is not possible as Howard Street is too far from Market Street for a practical pedestrian link. In addition, the two turns in Mission Bay at each end of Owens Street are mild, but would in some ways still slow down service.
    Pros Cons
    Curves & Tunnel Capacity
    • 1 major curve at 6th & Howard
    • 2 minor curves  at 16th and Owens and at Mission Creek
    • Improved train speeds

    • May require 1 medium curve from Howard to Transbay Center between 3rd and 2nd streets.
    • 6th and King Street Station between Townsend and Mission Creek. 
    • Howard and 4th Station.

    • Moves current Caltrain station 1 to 2 blocks west.
    Tunnel Alignments
    • Path remains below streets most of its length.

    • Path goes below private land and buildings at 7th and Mission, and near Transbay Center
    Access Opportunities
    • Access to Mission Bay, SoMa & Design District.
    • Transfers to N-Judah.
    • Access to Union Square & Mid-Market. 
    • Transfers to T-Third at Moscone Station.

    • No access to 16th Street Corridor or South Beach.
    • No additional links to BART.
    Length (19th Street to Transbay Center)
    • 2.1 miles, ~250 feet (-2%) shorter than Townsend 2nd Route
    • New EIR and engineering for the entire route
    • Probably equal cost of construction.

    • New EIR and engineering for the entire route.
    • Building extra stations (e.g. Mission & 5th St) adds cost.
    • Removing freeways has a strong track record in San Francisco. 
    • A Moscone station on Howard may be enticing.

    • Changing tunnel is politically challenging.
    • Moscone and other building owners may protest deep tunnel under them.

    The Simmons Howard has the great challenge, much like the The Grand Curve, of going right under Moscone Center. That being said, it's still shorter than the current planned Steamboat Rincon alignment, the Mission Bay station wouldn't shift too far from the current one, and a SoMa station on Howard would provide new regional transit access to this growing part of SoMa.

    Steamboat Rincon - The Planned Route: Townsend to 2nd Street

    The currently planned route, as shown before follows Townsend and 2nd Street and passes through three very sharp turns. Note that the current plan calls for the tunnel to start on Townsend at 6th Street, not at 16th Street as would be necessary if I-280 is torn down.

    Pros Cons
    Curves & Tunnel Capacity
    • 3 sharp curves: 7th & Townsend, Townsend & 2nd, and 2nd & Howard.
    • Very slow train speeds through entire path.
    • 4th & Townsend Station between 5th and 4th streets.

    • No 16th Street station or SoMa station.
    Tunnel Alignments
    • Follows under streets most of path. 
    • All right of ways have been cleared.

    • Requires additional tunnel between 16th St and Townsend.
    Access Opportunities
    • Access to North Mission Bay and South Beach. 
    • Close to AT&T Park. 
    • Transfers to T-Third and N-Judah at 4th & Townsend Station.

    • Access to UCSF Mission Bay requires crossing bridges. 
    • No access to 16th Street Corridor, or Potrero Hill. 
    • No new access to BART.
    Length (19th Street to Transbay Center)
    • 2.2 miles

    • Will require additional tunneling to go beneath 16th St and Mission Bay Blvd.
    • EIR complete and certified. 
    • Engineering planning already begun.

    • New EIR may be required for tunnel between 16th Street and Townsend.
    • $2.5 billion

    • Funding gap exists. 
    • Waiting for Federal Funding. May not be available until 2022.
    • All political forces in the city and state are in support of DTX.

    • Congress not reliable with funding. 
    • Removing I-280 politically difficult due to perceived traffic challenges.

    Advantages of TWO LINKS to BART

    As mentioned before, having a transfer link to BART/Muni Metro at the Transbay Center would greatly benefit regional transit. Although no link is actually funded or planned right now, there have been calls for it in previous Transbay studies. Such a connection could connect to Embarcadero, Montgomery or both stations. Unfortunately as BART recently showed, these two stations are nearly at capacity, as shown by their consideration of adding new platforms under the "saddlebag" proposal. If the only link between BART and Caltrain in San Francisco is at the Transbay Center, the BART stations may become overly impacted.

    That said, creating a second link between BART/Muni Metro and second Caltrain Station somewhere on Mission Street would reduce the demand such a transfer would have at Embarcadero or Montgomery. By spreading out transfer traffic to two stations, BART stations and the Transbay facility will not become overly crowded. Even if they don't become immediately crowded, having the two stations would allow for much more growth than the current DTX plan.

    In addition to transfer benefits, providing a Mission Street station linked to Powell or Civic Center would also allow for Peninsula and South Bay commuters to reach workplaces in the Mid-Market and Civic Center job centers. Likewise, shoppers could easily get to the Union Square and San Francisco Centre shopping centers.  All of this would add value to San Francisco's livability, workability and land value.

    2 Station solution spreads out transfer demand over 2 stations.

    One station transfer at Transbay could create capacity challenges at BART stations,.

    Final Thoughts

    Any of these ideas would create a great improvement in transportation on the Caltrain corridor and in San Francisco. The question is, if money isn't lined up now, and it may not be for a while, can we put the current plans on hold and find out if another tunnel alignment might just be better. Secondly, may of these plans may be better than the current plan. However, the cost to step back and redo environmental studies and new engineering plans may prove too costly. That said, without a reasonable review of said costs for each alternative, we don't know whether or not rerouting the tunnel is a fool's errand or a stroke of genius. 


    1. Just a little background - I've also created an 8th Street Mission alignment (Showplace Price alignment?). Much like the other Mission Alignments it would have a 7th Street Mission Station, but the Mission street station could be between 7th Street and 6th Street. This is near the Trinity Place Apartments and the new Federal Building. In addition it would only be three blocks away from the Twitter Headquarters at Mission and 10th Street. In addition it would be very close to all the Civic Center government buildings.

      Let me know if you'd like to see this map.

    2. This is a great idea. While I do worry that the so much TOD density has appeared near the current 4th/King station, and moving the station could negatively impact those people nearby, these plans would improve the trip for everyone and vastly improve accessibility. I'm not sure why they weren't considered before, but they should be! This project is a massive one, so let's think big about all the options!

    3. Excellent post with some lovely graphics.

      Rather than go to the expense of building a second downtown SF station, why not create pedestrian tunnels between BART/Muni at both Embarcadero and Montgomery stations? That would help distribute transfers without requiring too much extra expense.

      Personally I would go for a 7th/Mission station followed by a long smooth curve to Transbay. The highest priorities for the DTX should be speed and capacity.

    4. Evan, you're right that moving the Mission Bay Caltrain station too far from 4th & King would reduce their easy access to Caltrain. However, the Long Bridge and Simmons Howard plans only move it 1 or 2 blocks away which would have no real impact. Moving the station to 7th St between 16th Street and Mission Bay Blvd or even Townsend would be a bit farther. I agree such a move would be a negative for them if they relied on Caltrain. However, if the N-Judah were extended to the Mission Bay 7th Street station then they would still have easy rail access. Not as good as before, but still accessible.

      Jon, creating a tunnel to BOTH Embarcadero and Montgomery from the Transbay Center is possible, and it would presumably spread out some of the demand and thus reduce the stress on each station. That would probably address the capacity issues at BART stations, although since they're already at capacity, adding ANY demand is a bad thing until demand is spread out over more stations downtown. That's the whole reason of adding the 5th & Mission/Powell or 7th & Mission/Civic Center links. They allow for better access to more parts of downtown and don't cause overdemand at one station. Unfortunately adding one station on Mission Street with a tunnel link to BART would be a big additional cost. So I would propose that a realignment of DTX be built so that an additional station could be added at a later point.

      1. Sorry, by 7th & Mission I meant Mission Bay on 7th St, as in your Mint Harris alignment.

        The question then is, do you have a smooth curve from Mission Bay to Transbay, or two straights and a sharper curve, allowing a station to be added on a straight (e.g. under Mission) at a later date? Personally I would go for the former in the interests of speed and capacity. BART's capacity issues will eventually need to be solved by a second transbay tube.

      2. Jon, thanks for the clarification about the 7th & Mission Bay station idea. Interesting you bring that up, since I have often felt that naming stations "Mission Bay + a street name" could prove confusing with BART's current 16th St Mission Station. Imagine, if we had two new Caltrain "Mission" stations plus the 2 existing statinos AND a Transbay Center on Mission Street, we'd have a lot of confused travelers.

        • Mission Bay/ 7th Street
        • Mission 5th Street
        • 16th Street Mission
        • 24th Street Mission
        • Transbay Center (on Mission Street).

        That's why I've dropped the idea of using 16th Street in a Mission Bay station name. Having a 16th Street Mission Bay Station AND a 16th Street Mission Station is asking for trouble!

        I would hope that only one ped tunnel between Caltrain and BART would be sufficient. I just think that many new opportunities, and likely many more transit riders would be created with a Mission 5th St / Powell link. Hopefully adding new platforms would address all capacity issues at BART's downtown stations, even with added Transbay Center transfer traffic.

    5. First, kudos on all this grand thinking and graphic work. Your maps are par excellence. I would just like to point out that the "western" alignments, (e.g. Mint Harris, Grand Curve, and even Simmons Howard) I think are fatally flawed at the outset because of the buildings they would run under/through that could not be demolished or otherwise accommodate train running through them relatively shallow underground. Anything that shows an alignment cutting through/under Moscone, SFMOMA, the Pacific Telephone building, or major affordable housing sites (e.g. at 4th/Howard) are almost certainly non-starters. The train would have to be relatively shallow in these locations (<100 feet below ground) due to its approach to the max 60'-deep train box at Transbay, and you're just not going to obliterate these major institutions and buildings which have extensive below-ground facilities at or very nearly at the same depths your're looking at. While I'm not a rail engineer, the very tight S-curve approaching Transbay in the Grand Curve also looks very challenging, but I could be wrong. In my (not totally un-educated) estimation, the only possible re-alignments would involve an alternative Mission Bay alignment that still connected to the planned 2nd Street alignment north of Townsend. I just don't see any alternative way to get into Transbay without blowing up a huge swath of the southern side of downtown. So of the options you show, I think only a version of "Long Bridge" is practically feasible. Also, why aren't you showing the freeway-take-down version that eases the curve (along the freeway ROW) into the planned 4th/Townsend station? That is probably the most likely and practical re-alignment of all this.

      1. Dear Practical Not Quite A Rail Engineer, but Educated,

        You raise many good points, many of which I thought about but didn't fully highlight in the post. You're right that all the western alignments would require going under some buildings that shouldn't be destroyed (if a shallow tunnel were used), or that a deep bore tunnel couldn't make the slope from required depths to reach the somewhat shallow 60' deep Transbay train box.

        I'm no engineer, not a train engineer or a tunnel engineer. However, as you point out, there are some basic geometric considerations that we can work with. By my estimation, if the western alignments were deep bore (100' or deeper) most buildings and probably all buildings would not be affected by a tunnel at that depth. With the Moscone Center 40 feet below ground and the Central Subway 60-70 feet deep at Mission Street (and less deep at Howard), I would assume such a deep bore tunnel would work - even with 60 feet separating Moscone and a tunnel.

        However, you raise a big challenge. If a DTX tunnel is deep bore, is there sufficient length to change underground elevation from 100' deep at 4th Street and rise 40' feet to the 60' train box. I wish I knew the steepest "acceptable" slope for a train. With a 2000 feet separating 4th & the train box (~ 1/2 a mile), could the trains make the 40 foot climb? I don't know. And, as you point out, even if they could, at New Montgomery, and at 2nd Street, they would be a lot closer to 70 or 60 feet deep and likely affect the taller buildings near there (Pacific Telephone Building, Academy of Art), making the tunnel impossible without tearing down buildings - which is a nonstarter.

        The only other possibly way around this problem would be to have a western alignment follow Mission Street all the way to the Transbay Center. What I'd imagine would be one of two options (or both). To reach the train box at Transbay Center, the tunnel would have to turn at New Montgomery Street, going where some 3-6 story buildings are. I imagine the buildings would have to be condemned, unless there was some engineering way a building of that height could survive a 60 foot tunnel underneath it.

        The other idea would have the rail station go under Mission Street. I think this isn't practical considering the current box is already under consideration. I do however believe that one day, if a western alignment were created, that added capacity could be created with a Mission Street station at Transbay, but that's not for a long time.

        In conclusion, if a deep bore tunnel is not practical due to requiring too steep a slope to reach the Transbay Center, or the alignment would infringe on too many buildings close to the Transbay Center, then the Long Bridge alignment may be the best.

        With the Transbay Center’s train level 60 feet below grade

      2. "With a 2000 feet separating 4th & the train box (~ 1/2 a mile), could the trains make the 40 foot climb? I don't know."

        The answer is yes- 40/2000 is 2%, which is manageable by both the new Caltrain EMUs and High Speed Rail. High Speed Rail are planning a 3.3% sustained grade going over the Tehachapis, so anything less than that should be okay.

        That said, the Central Subway is so deep that you might be better with a shallow DTX tunnel under Mission and above the CS, and dive down an extra level to hit the train box.

    6. Thanks for posting this! However, won't any of the alignments passing beneath Moscone Center be considered moot due to the work being already done to connect both sides of the Moscone Center?

      1. Dear Moscone,

        Glad you like the post. I've tried to find some more information on the Moscone Center expansion plans. From the little I can find, it appears much of the expansion will be ABOVE ground, building more exhibition space and services at the current driveways on Howard Street. Underground, my hunch is that the area will be reworked, but nothing will go deeper than the current underground convention center facilities already under Howard Street.

        That all said, the same points and challenges I described in the reply to Practical Non-Engineer still apply.

    7. If you think about, they should have the extension with the "grand curve" and it should only be one station, at the Transbay Terminal since they are dubbing it as "the Grand Central" of the west. You dont want to diffuse ridership across 2 stations, Transbay Terminal will be able to handle the Massive amount of people coming from the peninsula and the rest of california. The reason for the curve, since it will handle high speed rail and you want it to go at a decent speed before it arrives at the "grand Central" of the west.

    8. Interesting subject.

      Tunnel? Don't be ridiculous, there's enough of that nonsense already.

      Why does the train station have to go to Market? You realize of course that the peninsula train station has been in that area since the 1870s or so. Suddenly it's a problem? There's a metro line, muni, a jitney, and taxis serving caltrain from downtown.

      But if you need to build a new train terminal, feel free, here is a good architectural model to emulate:


    9. The benefit of the powell street station connection is a little overrepsented here. If you're in the mission, it would be easier to take the 22 or 48 to 22nd street station. If you're further south on the bart line, then you should transfer at millbrae. So the only ones left are people from height/inner sunset that would benefit.

    10. Tak,
      Great comment. You raise an important issue. Sometimes when a great idea is promoted, its benefits are "overrepresented". Take the BART to San Jose extension for example. Ridership at Downtown San Jose is projected to equal current day Montgomery by 2030. It could happen, but I think this is a gross overestimation. (The numbers may not match up exactly, but Dwtn SJ is projected to be one of the top 5 stations in the system.)

      So I've been doing some number crunching to look at your point from a time point of view. I don't have the final numbers yet, but I'll have a comparison of how long it takes to get to Caltrain currently, to Transbay and to potential stations - all from various points in San Francisco. That will give us a time comparison, and a number of transfers comparison.

      That all said, I still believe that creating a 2nd Market Street or at least 2nd Downtown Caltrain station would greatly INCREASE ridership and use of Caltrain by San Franciscans. To speak to your point, I believe that many folks don't take Caltrain from the Mission or Noe Valley because they have to schlep on a bus to a dark and shady train station. In addition, my understanding is that transfers at Milbrae are not timed at all - but I'll have to check the schedules.

      Thanks for your comment. I'll have the travel time analysis in an upcoming post.

    11. So stick with me here cause I know I am going to be laughed at. What I would prefer to do is to link the stations in to one and instead of cal train to the east bay I would send it along the embarcadero north with a transbay tunnel into sausalito. Then push the SMART train south and have them connect so you could get from cloverdale to gilroy on the same train. The gauges are the same and minimal change would need to be made to accomadate becuase the new caltrain trains are similar to the SMART cars that are being purchased. Go ahead and tell how implausable it is that the Northbay communites would be ok with this but I honestly think that someday it could happen. I also understand that the tunnel would be longer then the current transbay tunnel and would cost a lot but I think it would be good for the north bay. Also they could propabbaly just tunnel the whole way instead of building a tube. Why build another transbay tunnel for a system that would have to start fresh in the east bay. I also dream of a treasure island bart station if they can ever develop the land and the bridge on ramps and off ramps correctly. Also does anyone know if they will combine the diridon station with bart? Because all the animation I have seen makes it seem like it will be accross the street from diridon.

    12. Congratulations on having a good transit brain. The only thing I do not like is that you are rather loose about the number of stops.
      It's fine for bus lines to have many stops; it's already a problem if BRT has many stops. Light rail should definitively have fewer stops than a bus line, but this can be comparable to the number of stops a BRT would have. A MuniMetro line should have fewer stops than a light-rail line, while an actual Metro would have fewer stops than a MuniMetro line. Regional Rail would have fewer stops than a Metro, but the distinctions between both can at times be hard to distinguish. Rail (Caltrain and HSR) should have fewer stops still (if they want to grow to their optimum state) or mix up their service (but they can severely hamper one another).
      Imagine taking the bus from SF to Los Angeles and it stops on every corner - no one would take that bus, not even for free.
      While I'm here: There is no such thing as transit. There are many different transit products and they all behave best in their own environment. MuniMetro is, for instance, a bad idea, because both the best of a light rail and the best of a Metro outperform MuniMetro individually. The benefits from a Metro (long trains, fast service) are not repeatable on the local streetcar lines; the benefits from the local streetcar lines (going to many different places, multiple lines do not bother each other) become a burden when all lines are pushed inside one tunnel.
      Rail is extremely expensive to build and the product must be optimized first before one can look for additional benefits. San Francisco should have just one rail stop for HSR (and Caltrain), except if there is an extremely good reason to stop elsewhere. Having a stop at 22nd Street because there is a bus stop is not an extreme benefit. A stop at a regional transit node would be a good reason (one could make the argument for 4th Street, Central Subway connection). But there is never a reason to add a third stop in the mix, wasting the core of the supposedly very fast product.
      A transit product is optimized when it attracts the most passengers. Just because MuniMetro is loaded to the max doesn't mean it attracts the most passengers; a real Metro (every train four cars long) would attract more passengers (and would also not leave the underground tunnel but have transfers to light rail lines with people getting home on average five minutes faster than today).
      Thank you for sharing your transit brain, this was fun for me to look at. You are right that the crookedest line is not a good idea.


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