12 December 2015

Optimizing the Midline Overtake

The most important piece of infrastructure required for "blending" HSR with Caltrain on the peninsula rail corridor is an overtake facility, basically a several-mile long stretch of up to four tracks that will enable faster trains to overtake slower trains.  Caltrain studies have shown that the best performance (measured by robustness to cascading delays) can be achieved with a midline overtake  from San Mateo all the way through Redwood City.  Preliminary engineering and environmental clearance for this infrastructure is now resuming, with the recent award of a $36 million contract by the CHSRA to engineering firm HNTB.

The baseline configuration for this overtake is described in Caltrain's blended operations analysis, and assumes rebuilt stations at Hayward Park, Hillsdale, Belmont, San Carlos and Redwood City with four tracks and outside platforms in the tried and true style of the 1930s Pennsylvania Railroad. High-speed trains would use the center pair of tracks to overtake slower trains on the outside pair of tracks, as shown below (click figure to enlarge):


For comparison, the figure also shows a better solution that ensures the highest level of punctuality for all trains using the corridor.  This optimized overtake configuration differs from the baseline configuration as follows:
  • The slow trains run in the middle, so that disruptions to local commuter service (for example, when an incident blocks a track for hours) do not disrupt high-speed service when commuter trains are re-routed around the incident location.  This track configuration is known as Fast-Slow-Slow-Fast (FSSF) as opposed to the traditional SFFS.  Real world examples of FSSF can be seen in train cab videos from Sweden and Australia.
     
  • All commuter stations are built with central island platforms.  This allows commuter trains to use either platform face without confusing passengers, and requires only one set of station amenities (shelters, elevators, escalators, stairs, ticket vending machines, PA systems, train arrival screens, lighting, benches, etc.) because there is only one platform.
     
  • A major new interchange station at Redwood City, with four platform tracks and additional train storage sidings.  This station (described below) would serve as a transfer point for HSR, Caltrain and future Dumbarton trains, as well as non-rail transportation modes.
     
  • A carefully planned future-proofed high-speed rail junction where the Dumbarton rail corridor meets the peninsula rail corridor, preparing for the inevitable arrival of passenger rail service across the Bay.
Here's how it would ideally play out.

Short Term: the San Mateo Grade Separation

Preliminary rendering of new
Hillsdale station with island platform
The next step in the decadal process of grade separating the peninsula rail corridor will soon begin in San Mateo.  A new $180 million grade separation project is in the final stages of planning for 25th Avenue (currently a grade crossing) as well as 28th and 31st Avenues (currently not connected).  Concurrently with this project, the busy Hillsdale station will be moved a bit north of its current location and turned into an island platform.

This project is caught in an interesting political bind.  There is on one hand a rush to complete it by 2019 before Caltrain's electrification project, to minimize disruptions to Caltrain service.  On the other hand, due to its strategic location, this project will form a key building block of the blended system with HSR, which still needs to be environmentally cleared.  It is a near certainty that this portion of the corridor will require four tracks to enable trains to overtake each other, but any attempt to design and build it as such is likely to run afoul of HSR opponents who will accuse the CHSRA of advancing their project through CEQA piece-mealing.

The southern San Mateo grade separation design will have to be very carefully considered to preserve the ability to add two additional tracks with as little disruption as possible.  Road underpass profiles and bridge abutments should be designed for four tracks, as should the elevated structure that will support the tracks.

The choice of an island platform configuration for the new Hillsdale station is either a sneaky way to build a wide four-track embankment in preparation for yet another new station with SFFS outside platforms, or is an excellent choice for FSSF because it allows future tracks to be added without rebuilding the station for a second time.  One hopes the station access (stairs, ramps, etc.) will be designed to allow the platform height to be raised easily from 8" to 50".  An intelligently designed San Mateo grade separation would atone for the terrible failures of the San Bruno grade separation, designed with great hostility towards higher speeds or additional tracks.

Medium Term: Redwood City HSR Station

Amsterdam Bijlmer (photo by tataAnne)
could just as well be the future
Redwood City train station.
While the CHSRA's plans for a mid-peninsula stop have been shrouded with ambiguity for several years, Redwood City stands out as a more optimal location for a new HSR station than Palo Alto or Mountain View, the other two locations in the running.  Unlike its neighbors to the south, Redwood City favors strong urban growth, has a large amount of railroad land available, and is reasonably well-connected to the existing road and transit network.  Redeveloping the antiquated but popular Sequoia Station shopping center would enable the construction of an elevated four-track station with plenty of capacity to support not just HSR but also Caltrain cross-platform connections and future Dumbarton service.

The station complex would feature two shared (HSR or Caltrain) 400-meter island platforms centered between Broadway and Brewster, easily accessible from both streets.  Bus connections would be conveniently located under the station. To the north of the platforms, a pocket turnback track would allow Dumbarton trains to reverse without fouling other traffic.  Similarly, to the south of the platforms, another pocket turnback track would allow southbound Caltrain locals to terminate in Redwood City before turning northwards again to serve the densely-spaced stations of San Mateo County, allowing Caltrain to serve more passengers with fewer trains and crews.  Thanks to the FSSF configuration, all this to-and-fro by commuter trains would stay well out of the way of HSR.

This would be a large train station and quite a tight fit (if you're curious about exactly how large and how tight, download this KML file into Google Earth to view the station footprint and track layout).  It would be a big change for Redwood City, but with a huge payoff: the tracks would no longer form a barrier through town, and the Sequoia Station shopping center would be merged with the station to form a gateway and a destination in its own right that is connected to downtown.  HSR service could make the city a very desirable location for business.  The new station could become the centerpiece of the ambitious revitalization strategy described in Redwood City's downtown precise plan.  But this idea is not without pitfalls, as the size of the station could be compared to plonking a couple of Nimitz-class aircraft carriers in the middle of town.  To use the tired slogan, it needs to be done right.

Medium Term: a New Fair Oaks Station

Approximate location of new Fair Oaks
station island platform, view to northeast.
Overtake would extend just beyond
platform to the right (south).

The key to reliable overtaking on a multiple-track railroad is to ensure that the average speed of the slower train being overtaken is sufficiently slower than the average speed of the faster overtaking train.  One of the ways of ensuring a good speed differential is to have the slower train make station stops that the faster train doesn't; each station stop is worth about 2.5 minutes.  Therefore, locating stations on the four-track overtake section is helpful.

This brings us to a lemon of a station immediately south of the midline overtake: Atherton.  Located in an area of very sparse population and jobs density, Atherton should be permanently closed.  This closure would come not only as a show of appreciation commensurate with the town's support of Caltrain modernization, but especially because census data shows clearly that Atherton is precisely where you would never place a train station.

To replace Atherton, a new Fair Oaks station should be built just 0.6 miles to the north, at the 5th Avenue grade separation.  The overtake section would be extended a bit southwards, just beyond the station, enabling locals to be passed while stopped at the central island platform that can be accessed from either side of 5th Avenue.  The new Fair Oaks stop would be equidistant from Redwood City and Menlo Park, and located in an area with very high population density that could support thriving ridership, in contrast to Atherton.

Longer Term: a Seamless Dumbarton Connection

Dumbarton rail has been an uncertain prospect for decades, with some political backing but insufficient funding.  While it may take another few decades for the money and the will to finally materialize, large concentrations of employment and the need for additional transbay corridor capacity make some form of passenger rail service inevitable.  The Dumbarton corridor also happens to be ideally suited for high-speed rail.

The key node is Dumbarton Junction, which should be reconfigured in such a way that trains can enter and leave the peninsula rail corridor swiftly and seamlessly.  This will likely involve a flyover track, enabling southbound trains to enter the Dumbarton corridor without crossing (and therefore blocking) any of the northbound tracks.  To minimize the altitude of the flyover, the Rte 84 / Woodside Road overpass would be turned into an underpass.  As for the Redwood City station, the fit would be quite tight with a 90-foot corridor width where the flyover track begins.

While the flyover may seem like an expensive solution to a problem we don't yet have, planning for it now (if not actually building it) will save money in the long run when passenger rail service grows.

Design Values

No matter how the midline overtake is ultimately configured, it must reflect design values that are clearly articulated.  One of these values should be compatibility between Caltrain and HSR.  It's not enough to talk about the "blended system" without actually taking the steps to make the two systems seamlessly interoperable, allowing any train to use any track to serve any platform.  This means no tracks can be dedicated to one operator at the exclusion of another.  Everything must be shared, including the platforms at the new mid-peninsula station.  This sharing contributes to another important value, robustness to service disruptions.  The fast-slow-slow-fast track layout is the key to ensuring that a commuter train delayed in Belmont won't create a statewide domino effect that eventually makes a train late in Los Angeles.  A third important value is future-proofing.  Infrastructure like the midline overtake will define what is possible (and not) for generations to come.  It would be short-sighted not to plan for a fast and seamless connection to the Dumbarton corridor, even if its future use isn't well-defined today.

The midline overtake is the key to an effective blended system.  When evaluating its design, ask yourself: is it compatible?  Is it robust?  Is it future-proof?

57 comments:

  1. If the narrow confines of Downtown San Mateo can be accounted for, how much utility would be gained by triple-tracking (or even quad-tracking?) from the Northern extent of your proposed overtake all the way up to Millbrae? If you're already doing 10 miles, adding 5 more to complete the widening between the two peninsular stations might add a great deal of flexibility.

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    1. >how much utility would be gained by triple-tracking (or even quad-tracking?) from the Northern extent of your proposed overtake all the way up to Millbrae?

      A lot, but the area north of SM city is Burlingame. As you're probably already aware, a city that is very hostile to any rail development (especially with the recent spate of suicides involving Caltrain they're having). However, SMC and RWC are both not hostile to HSR (I would even go so far to say supportive) and the area between them, Belmont and San Carlos, have already been grade separated and have space for quadtracking. South of RWC is Atherton, who needs no introduction.

      At least how I see it, Caltrain is focusing on the part of the line that they can most quickly develop. Once SMC-RWC is quad tracked and grade separated, cajoling Burlingame, Atherton and Palo Alto into it will be easier.

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    2. San Carlos does not have space for quad-tracking if the "TOD" scheme, on the exact land used for "shoo-fly" tracks during construction of the current San Carlos station, goes ahead. Per Clem, as best I recall. Clem has a post somewhere, which shows the dumbass[1]-business-as-freight-train-usual catenary going through the buildings.

      [1] as evidenced by specifying AREMA good-for-deferred-maintenace-but-shitty-for-pasenger-train turnouts at all points which aren't "High speed", in CHSRA's relevant Technical Memorandum (TM).
      I might be oversimplyfing, but not much.

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  2. The optimized plan looks far superior to the baseline plan, and may actually cost somewhat less (not taking into account the Dumbarton flyover).

    A minor flaw of the FSSF scheme is noise; with SFFS, you have a few meters more distance. But this can be kept under control using suitably designed noise barriers.

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    1. I doubt that will make much difference. For every southbound that is 15 feet closer to someone's house, there is a northbound that is 15 feet further away. Caltrain top speed will eventually rise to 110 mph, so I really doubt that SFFS vs. FSSF will make an iota of difference where noise is concerned. The real benefit is from the removal of grade crossings and the associated horn blowing.

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    2. I fully agree about the excessive horn blowing (and then also dump that stupid ding-ding-ding at stations…). As said, it is a minor flaw, which can be kept under control.

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    3. Front page of today's Daily Post:
      Atherton eying Caltrain "quiet zone" again

      I get a chuckle out of where the Atherton Councilman Mike Lempres says "a lot of the noise comes from the friction between the train and the tracks" and goes on to point out Atherton can hear train horns blowing for Redwood City crossings when ALL FOUR of Menlo Park's crossings -- Encinal, Glenwood, Oak Grove and Ravenswood -- are closer to Atherton than Redwood City's nearest crossing at Chestnut.

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    4. hi Max,

      My primary interest these days is model trains. But (to steal a quote), I could eat a handful of iron filings, and puke a better design than Caltrain/CHSRA's contractors have done. (Which is not hard; I have many, many photo-books showing European (and Antipodean) Hbf-en. I like to model, or at least plan out, train arrivals, shunting and departures; TEE 6/7 in Basel and cutting off/adding cars to/from Chur &c, is a favourite. (I wish I had space to model that in Spur-1!).

      It really, truly doesn't take much eperience, even at model-operator level, to appreciate how bad the local Transport-Industrial complex is.
      Deal with one stuck turnout, and the DTX design *stinks*.
      Mind you, that's off-topic for the current post.

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    5. Max,
      I live at the end of a canyon, a good 3km away from the railway tracks.
      Up a hill, then a right-angle turn and another 750m or so into the canyon. I still get woken up occasionally by horns (though much less than when I lived closer to the tracks.) I certainly hear the UP movements on quiet evenings. They're *loud*.

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  3. Just to understand, is what you're saying what they actually intend to do as the optimized plan, or another example of a better idea being skipped by planners?

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    1. An idea that I hope they consider carefully.

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    2. Have you seen any evidence that either Caltrain's employees or consultants read your blog?

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    3. You (and other technical bloggers) may have more of an audience than you think. Caltrain's RFP for EMUs is suspiciously similar to your blog posts on the subject, and I am inclined to think that it is more than coincidence. Alon Levy's research on subway construction costs has been referenced at fairly high levels throughout the industry and he's just a blogger doing it as a hobby like yourself.

      With that in mind, you should strike while the iron is hot and reach out directly. But there are so many suggestions on this blog that you can't bring them all up at once without getting dismissed as a meddling crackpot. Pick the 1 or 2 most important suggestions, find the head of Caltrain's planning or engineering division, and go for it.

      When choosing the suggestions I would pick ones that are (1) still very much up in the air, rather than settled like CBOSS and (2) have the greatest effect on operations and passenger experience, rather than on costs and community impacts. At least as a starting point, anyway. The reasons being that nobody will care what it cost 20 years from now if it is built right and popular, and community impacts (and indeed the power of the NIMBY lobby) are universally exaggerated.

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    4. Unknown, I pretty sure Clem was being facetious

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    5. CBOSS is — if there were anybody performing any sort of management at SamTrans/Caltrain — indeed "very much up in the air".

      The sunk costs (consultant payola) are indeed staggering.

      But the costs still to come are comparably so, especially as the system isn't working today and is all but designed and guaranteed never to work. It's speciality consultant designed to be unique, after all. Like venereal disease, it will be the gift that keeps on giving and giving and giving.

      Any competent manager, or even any borderline self-preserving self-serving manager, would choke it, strangle the consultants, put out a ERTMS/ETCS/GSM-R RFP (competitive procurement, noooooooooooooo.......), and vigorously finger point at the previous complicit administration (even if it really is the exact same cast with a superficial change in Maximum Leader.) "Mistakes were made."

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    6. You are insinuating that the business model would place a priority on lower cost to taxpayers and better (safer) service for riders.

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    7. And this is the Clem who hopes to influence the Transport-Industrial complex with aforesaid business model?!

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  4. >It would be short-sighted not to plan for a fast and seamless connection to the Dumbarton corridor, even if its future use isn't well-defined today.

    Are you suggesting that Caltrain would run trains to Hayward? I'm not against the idea, but you'd effectively have two BARTs then. At that point, why not also rebuild the rail bridge/pier next to the San Mateo Bridge and run trains across that too?

    I'm just spitballing here though.

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    1. It's not entirely duplicative. Dumbarton rail service would provide access to upper peninsula jobs which are not served by BART.

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    2. Why not? There is no existing RR ROW between Hayward rail lines and Caltrain in the San Mateo Bridge corridor. Dumbarton corridor has one; San Mateo Co. (Samtrans/TA) acquired it from SP/UP about 25 years or so specifically for future passenger/transit rail service.

      Also, today at least, there's a leg of the wye at Redwood Junction which allows trains coming off of (or entering) the Dumbarton line to turn onto (or from) the Caltrain line to the south of Redwood City without reversing. This means you could run trains across Dumbarton to/from Palo Alto, Mountain View and Sunnyvale without reversing.

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    3. Sure, but how exactly would that system work? At least how I see it, the most "realistic" option here would be a VTA extension that runs down Middlefield Rd. to the existing branch, then over the bay, then up Thornton Av. in Fremont. The only problem with this idea is that the train would have to go through a new ROW in Atherton.

      I suggest VTA because running Caltrain from SF to Fremont is redundant (as BART exists), and that east bay residents would want access to the jobs along VTA's lines. Alternatively, Samtrans could run their own light rail from San Mateo to RWC then to Hayward.

      This is all just fantasy though, again I'm spitballing.

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    4. Ideally the rarely used Oakland Subdivision (the set of tracks that goes right next to the BART stations in Alameda County, Oak Coliseum to Union City) could be taken over and used exclusively by the CC/Dumbarton Rail. The main problem I see with Dumbarton Rail is that as soon as you get into Fremont, you're sharing trackage with UP that they will jealously fight tooth and nail over.

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    5. As far as I can tell, the most "direct" route from Newark to Fremont BART is along the existing line that ACE uses. Assuming UP or ACE won't play ball, the line could just be run up Thorton Av.

      Alternatively, it could make a northward turn, and go along Fremont Bvld. into the Capitol Corridor's Hall station or into Union City BART. The goal here is to avoid UP's tracks entirely, especially when a newer line provides better connectivity/access to areas not served by CC or BART.

      Alternatively, it could also run up Hesperian up to Oakland Intl, as a slower BART.

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  5. Interesting that the grade separation plans for Hillsdale are for a center platform while the mid-line overtake plans are for outside platforms. Since the 25th Ave/Hillsdale grade separation will likely happen first, maybe they'll redesign the mid-line overtake with center platforms FSSF. (Plus then Belmont Station wouldn't have to be rebuilt either!)

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    1. I sure hope that will be the case. Unfortunately there is a fairly entrenched (but totally mistaken) view that FSSF would cause express trains to "slalom" around Caltrain stations. The physics of very large curve radii does not bear this out.

      It's the horizontal version of something that we saw in the preliminary engineering back in 2010, where the vertical profile was kept artificially flat (resulting in long viaducts on stilts) to avoid a "roller coaster" effect that didn't exist.

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    2. So I dredged up an old post about roller coasters. I might have to write another one about slaloms...

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    3. "slalom"? Clem, just how little grasp are you insinuating that the denizens of the Caltrain Bunker have of basic high-school Newtonian dynamics?

      "None at all" seems to be what you're saying. Am I mistaken?
      F = d(mv)/dt = m(dv/dt0 = ma, a = v^2/r

      Centripetal force... and the of rest Newton's Principia, is all Greek to Caltrain?

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    4. IIRC, Caltrain's objection to FSSF was that it would require a miniscule amount of additional property acquisition.

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    5. While I support FSSF, I don't know how Caltrain would transition from SFFS (like it is at Lawrence and Bayshore) to FSSF. Even if they're in different places, it seems to be confusing to have SFFS and FSSF tracks on the same line.

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    6. There should not be much of a problem, because the 4-track section is "self contained" (well, more or less), which means that it spreads from a two-track section and joins again into a two-track section. For the passengers of the local trains, there is not much of a difference anyway… through an underpass and up to the platform.

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    7. For passengers, FSSF to SFFS is the same as doors opening on a southbound train on the west side at Hillsdale, east at Belmont, and west again at San Carlos. For trains, as F and S trains will still be sharing tracks at some locations, it's an issues scheduling to merge and unmerge the trains.

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    8. And scheduling to merge and unmerge trains, of course, has nothing to do with SFFS or FSSF.

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    9. Switching between SFFS and FSSF is a non-issue particularly when there are two track sections between them.

      Doors sometimes open on the right, sometimes on the left.

      And so what? ... this already occurs on Caltrain, and is very common on systems around the world.

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    10. I think the concern might be what happens when one four-track section is extended to meet another. When there isn't a two-track section in between, suddenly SFFS meets FSSF and we have problems.

      To that, I would say that the very short SFFS sections that currently exist (Bayshore, Lawrence) can be reconfigured for a tiny fraction of the costs that would be incurred in quadrupling such a large portion of the corridor. It is a fallacy to think that the new midline overtake should be SFFS simply because Bayshore and Lawrence were built that way.

      Another argument that one could make is that the blended system will use primarily two tracks (that law isn't a joke, is it?) so that the situation of two four-track sections being extended to meet each other would never arise in the first place.

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    11. Would Bayshore really be a problem going from FSSF to SFFS? I'm thinking that HSR won't be traveling that fast that switching on approach to Bayshore wouldn't be a problem. In fact, this is exactly what happens today when the Bullet overtakes the local at Bayshore. On the shared northbound track leading into Bayshore, the Bullet switches to the inner passing track to bypass Bayshore (SFFS). So a northbound HSR on the outer track (FSSF) would simply switch over to the inner track leading into Bayshore becoming SFFS there.

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    12. A switch between FSSF and SFFS is, for all practical purposes, a two track section.

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    13. A less practical switch between SFFS and FSSF would be a 2x2 tunnel or viaduct. While it keeps a continual quad track with the width of a double track, the approaches on one end of the tunnel would have to be demolished and rebuilt if Caltrain is looking to use only FSSF or SFFS. Also I think that a 2x2 structure isn't as earthquake resistant.

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    14. What's a "2x2 tunnel or viaduct"?

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    15. ... and how do you mean it allows a less practical switch between SFFS and FSSF?

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    16. I thinks Daniel Kufer is referring to a setup with flyover/unders. But the current amount of SFFS track is so small that nothing like that could ever be justified on a cost basis.

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    17. This is what I meant: http://caltrain-hsr.blogspot.com/2010/02/stacked-nonsense.html

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  6. A sensible plan, but looking at the existing grade separations it's hard to see how you could add two outside tracks without significant property takes on the east side of the alignment. In many places the tracks are right up against Old County Road, in other places there are properties right next to the elevated tracks.

    A better approach might be to build the two new tracks on the west side of the alignment, which mostly consists of parking lots and wasteland. This approach would be compatible with either FSSF or SFFS.

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    1. When adding two tracks you bump out in whatever direction (east or west) that is easiest (least costly/painful). So yeah, in some cases your 4-track "footprint" bumps out to west and maybe in other areas to the east ... or some combination thereof.

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    2. That's an excellent point. Tracks, signals and overhead electrification can be rejiggered as needed to fit whatever substructure (e.g. grade separation) is feasible to build based on the available space and constraints to the right of way. To think of tracks, signals and poles as unmovable once they are placed isn't correct--it's a pain, but they can be moved.

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    3. Tracks are easy enough to move; I was more thinking about the platforms. If you consider a station like Belmont, where it clearly makes more sense to build another two tracks on the west side of the station, you have several choices.

      You could create a duplicate of the existing two tracks plus island platform to the west of the existing station, giving you an express train compatible station that works with either FSSF or SFFS.

      Or, you could demolish the existing platform, move the existing southbound track next to the existing northbound track, build an island platform in the space freed up by by the southbound track, and add two new tracks to the west, giving you an island platform FSSF local station.

      Or, you could demolish the island platform and move the existing northbound track next to the existing southbound track, build an outside platform in the space freed up by the northbound track, and add two tracks plus an outside platform to the west, giving you a SFFS local station.

      Or, you could just do a bunch of property takes to the east of the existing station, and add a track to the east and a track to the west for a FSSF local station.

      I don't know which option is the cheapest and most constructable with the fewest community impacts, but I suspect this will be a significant factor in what ultimately gets built. This time round CAHSR will be on a tighter budget and will not want to alienate the Peninsula any more than they already have done.

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    4. That exact sort of trade-off exercise will have to be conducted at every station where quadruplication will occur.

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  7. One thing of note: all the improvements suggested by Clem can be apply to SFFS operations as well except for the tail tracks at Redwood City, where they would be located outsides of the Slow tracks instead of in the center.

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    1. And most station should be reconstructed with two island platforms, instead of side platforms as in the Caltrain's Blend Operation Analysis.

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    2. And this exemplifies one of the reasons to prefer FSSF - if you have the local trains on the outside, then short turns conflict with basically everything.

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    3. Depends on how much money you want to spend.

      https://en.wikipedia.org/wiki/North_Brunswick_(NJT_station)

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    4. Okay sure. You can short turn trains without eating capacity on all tracks if you have a flyover. Which makes sense for NJT, because the NEC is SFFS anyway. But in CalTrain's case all this is more or less built from scratch.

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    5. Don't have to change ends with a flyover/duckunder.

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    6. In what world is that actually an overruling concern?

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    7. If a nice four track line has 14 15 maybe in some dystopian future, 16 or 17 trains an hour why is four or five trains an hour crossing the tracks a problem?

      There's other solutions besides flyovers/duckunders. Two island platforms, the train that is turning can follow the express to the center tracks and turn around in the pocket tracks.

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    8. Or you can just build it FSSF and be done with all that, just sayin'

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  8. Just an update: mid-Peninsula station is no longer being considered
    http://mv-voice.com/news/2016/05/06/high-speed-rail-team-makes-whistle-stop-in-mv

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