07 May 2016

Caltrain Has a Dwell Time Problem

Actually, Caltrain has two dwell time problems. The first is that station dwell times are too long, and the second is that station dwell times are too unpredictable.  Both of these problems will prove fatal to the blending of Caltrain and HSR services on "primarily two tracks."

To help visualize why, let's use position-versus-time string diagrams, often discussed on this blog.  Imagine trains following each other on a single track that runs from San Jose to San Francisco (ignore the other direction for now).  This red line is a local train making a lot of stops.  It leaves San Jose, and a while later arrives in San Francisco.  If you looked really closely you might see the individual station dwells, small horizontal kinks that occur whenever the train is stationary and time passes, but when you squint, it looks pretty much like this:
Every once in a while, this local train comes to a station where Jane, a wheelchair user bound for San Francisco, would like to board.  Because we don't have level boarding, getting Jane on board the train involves manually deploying lifts or ramps to ascend the several steps from the platform into the train.  Conductors must help Jane through the mechanics of the boarding process, which can easily take several minutes but feels like an eternity, even for Jane.  Timetable planners allow for riders like Jane by making sure that no other trains are scheduled right behind each other, to absorb these randomly occurring super long dwells without causing a train traffic jam.  They call it padding.  Here's what padding looks like, in pink:
This being a blended system on "primarily two tracks," we've got express trains and even high-speed trains using the same track as Jane's local.  A faster train looks like this blue line:
The blue line is steeper because the express train can cover the same distance from San Jose to San Francisco in much less time.  Here comes the express behind the local:
The timetable planners don't want the express to be delayed.  That's why they left a big gap between the trains, giving the local a good head start out of San Jose so that the express won't catch up to it before San Francisco.  Alternately, here is the local departing San Jose right behind the express:
Once again, a big gap opens up behind the express because the local is so much slower to arrive in San Francisco.  Now it's rush hour, and this is what "blending" soon looks like (not to scale):
In one hour, six trains can arrive in San Francisco.  Our string diagram is full of gaps, which means we are making very poor use of the capacity of our single track.  How do you fix this?

First, you electrify Caltrain.  While this isn't cheap, one of the main advantages of electrification is that EMUs start and stop much more quickly, so that on average, a local can get to San Francisco several minutes sooner while still making the same station stops.  The local will have a higher average speed than it did before.  Compare:
See how the new EMU local train shows up as a steeper line?  That's because it spends less time moving between stations.  (Note to Atherton: electrification is not just an emissions thing.  Tier IV diesel trains can't pull off this neat trick like an EMU can.)  Now this is what the "blended" rush hour looks like:
If you compare it carefully to what we had before, we can now fit eight trains in the span of one hour, instead of six, because those dreaded gaps are shorter.  By increasing the average speed of the locals, we were able to squeeze in more trains (and more passenger capacity).  Caltrain seems content to declare victory and live like this happily ever after.  This is what they envision as the "blended system".  Whenever Jane decides to ride the train, the pink padding still ensures that following trains aren't delayed too badly.

It's better, but still kind of mediocre.  Especially for Jane.

What if the local train could spend less time standing still at each station?  Dwell time can be reduced by level boarding, a step-free and gap-free configuration where you simply walk on or walk off the train, just like when you ride BART.  For a given number of passengers getting on and off the train, level boarding shaves off about 1/3 of the station dwell time since they can all shuffle on and off more quickly and seamlessly.  The magic of reducing dwell times is that while the train's actual speed is no higher, it still gets to San Francisco sooner, because it saved a few seconds during each station stop.  A few seconds here, a few seconds there, and pretty soon you're talking several minutes.  The average speed went up without the actual speed increasing!  The string for an EMU local with level boarding now looks like this:
If the local arrived in San Francisco ten minutes earlier thanks to electrifying Caltrain, it can arrive another five minutes earlier than that by having level boarding at all stations.  Electrification saves time between station stops, and level boarding saves time during station stops.  The two work together as perfect complements to each other.

The diagram above is actually wrong, and here's the second amazing thing about level boarding: Jane can get on and off the train like everybody else.  Not only does this give Jane the dignity and equal treatment that she deserves, but it saves everybody else the grief of those randomly occurring Jane delays.  Because dwell times are now predictable, timetable planners can get rid of the padding they applied in case Jane wanted to ride before.  Like this:
If you like probability distributions, here is the effect of level boarding on the probability distribution of dwell time:
Caltrain commissioned a study of station dwell times, which found that across a sample of 5149 station dwell observations, the median duration from wheel stop to wheel start was 49 seconds.  The median excludes abnormally long dwells, such as those occurring when Jane wants to ride.  The average dwell time does account for Jane and is 58 seconds, practically an eternity.  That was back in 2010.  Today, with the system bursting at the seams, average dwells are getting so long that the timetable was recently adjusted to make chronically late trains into slower on-time trains.  With level boarding, typical dwell times could easily be cut to 30 seconds.

Level boarding really improves the situation for rush hour:
We're really cooking now.  We can squeeze 12 trains through in one hour on the same track.  That represents a massive capacity increase, with the combined effect of reduced and predictable dwell times providing a similar benefit as electrification alone did.

Caltrain staff just doesn't seem to get this, and they are certainly not helping their board of directors understand the issue. They think of level boarding as primarily an optional comfort feature. Here is their view of level boarding, from a recent board meeting quarterly update:

First of all, they don't even call it level boarding. Dual doors!  What a pain!  Requested by interloping stakeholders, or imposed by those annoying HSR people!  Ew, it's so complicated!  It costs $30 million to equip the new fleet!  It's almost as if they are disowning the very idea of level boarding, and reluctantly trying "not to preclude" some unspecified future decision because this stuff is just too hard to think about.  Presented this way, you couldn't blame the board or the public for thinking this is a stupid idea.  Where's the upside?

The upside is this: dual doors are the only realistic path for Caltrain to achieve level boarding, and level boarding is the only way that the blended system can work on "primarily two tracks."

This issue cannot be taken lightly, because the next opportunity to start a Caltrain conversion to level boarding will not occur until 2050, when the new fleet reaches the end of its useful life.  That's because the new fleet, as about to be ordered, cannot provide level boarding at a platform height of 25 inches.  The entire system would have to be shut down for the trains to be modified and all platforms to be rebuilt at that height.  So, doing nothing today and blindly kicking the can down the road until 2050 is not an option.  A prudent and strategic $0.03 billion down payment for a gradual transition to level boarding is minuscule as a fraction of the $2.2 billion modernization budget, and unlocks great potential for quicker and more punctual commutes as soon as the next decade.

Dual doors are a customization that amounts to less than 5% of the price tag for new trains ($30 million out of $648 million bid price).  They can hardly be used as an excuse for the massive increase in the cost of Caltrain modernization.  They will help to address Caltrain's dwell time problem.

Caltrain has a dwell time problem.  The first step is for everyone (staff, board and public) to understand it.

13 February 2016

Train Control Update

There have been two recent and important developments in the area of train control systems, the safety systems known in U.S. parlance as "Positive Train Control" or PTC.  Both of them have a direct impact on the future of the peninsula rail corridor.

CBOSS Goes Sideways

Caltrain's CBOSS project, criticized for years on this blog, is in ever deeper trouble.  According to Caltrain's latest project update, the $231 million previously allocated for this project are nearly spent, but the project is way behind schedule and struggling in the most perilous and delay-prone phase of all: testing of the integrated system.

Not Ready for FRA
Testing is where it all finally comes together, not in the carefully controlled environment of a lab test bench, but in the real world with all its ugly imperfections, annoying glitches, and external influences.  In each segment of the railroad, three things have to happen in sequence: (1) everything has to be fiddled with until it works; (2) when everything works, a dry-run of the official acceptance test, known as "Pilot Testing," is performed; and (3) the system is formally accepted after passing the official FRA-witnessed test of all its functions.  Caltrain's project is stuck in the "fiddle with it until it works" phase, helpfully diagrammed as an infinite loop in the test flow diagram at right, extracted from a CBOSS Verification, Testing and Inspection Plan filed with the FRA.  This is where the schedule and budget are blowing up, with Caltrain's next step described as "Complete Segment #3 Pilot Testing and FRA Witness Testing," coming as soon as they are "Ready for FRA," whenever that may actually be.

Caltrain's update mentions "software release delays" relating to the I-ITCS product that CBOSS is based on.  There are worrying signs that I-ITCS may become a technological dead end: the company that makes it, GE Signalling, was recently acquired by French rail giant Alstom.  Alstom's mainline signaling product portfolio does not give it top billing.  Furthermore, the FRA process is described as being "in flux", meaning that the goal posts are moving.

What we have here is a classic foundering IT project, and it isn't clear if throwing more money at it (at a burn rate of about $50M/year) is going to save it.  With the federal PTC implementation deadline now pushed out to 2018, this is a good time to stop and re-assess the project before escalating the commitment.

HSR Buys Radio Spectrum

Meanwhile, the California HSR Authority is about to spend $50 million to secure the rights to a key chunk of radio frequency spectrum.  The frequency bands being purchased are 757-758 MHz and 787-788 MHz, not the usual 220 MHz band used for freight PTC systems.  Instead, the CHSRA has documented its intent to deploy ERTMS, an increasingly mature and proven train control standard that originated in Europe and is increasingly in worldwide use.  The two bands purchased for HSR are not sufficiently wide to deploy GSM-R, the obsolescent communications standard currently used as part of ERTMS.  It is more likely that California's deployment of ERTMS will use a more modern, secure and spectrum-efficient LTE communications layer, following the evolutionary path beyond GSM-R already being planned for ERTMS.

Connecting the Dots

Suppose the following conditions come to pass:
  1. CBOSS proves unworkable (increasingly likely)
  2. HSR shifts its focus to Northern California (possible)
  3. HSR finalizes plans for ERTMS as its high-speed train control standard (very likely)
  4. Due to construction delays, HSR needs new and productive ways to spend federal funds that expire by 2017 (possible)
Then an opportunity exists to deploy a train control pilot project on the peninsula rail corridor, using ERTMS with LTE communications in the 700 MHz band.  This scenario recognizes an important fact so far disregarded by Caltrain, that HSR will become by far the largest tenant railroad on the peninsula.  Ignoring this fact is an odd position to take for a railroad that hangs its future on "blending" with HSR.  Caltrain will surely dislike the idea, bleating about closer headways, crossing signal integration, station stop enforcement and other completely unproven bells and whistles--as they have since 2009--but events are now quite clearly bearing out the relative technological merits of ERTMS and CBOSS.  It's just sad that it took a quarter of a billion dollars to settle the question.

In the unforgiving world of system integration testing, reality always wins.

02 January 2016

Special Provision SP01040

Buried deep in the fine print of Caltrain's electrification Request For Proposals, Volume 3, Part C, Paragraph 1.04, you will encounter Special Provision SP01040.  It defines where and when the electrification contractor will be allowed access to Caltrain's tracks to perform the work of re-signaling and electrifying the railroad.  These are known as "work windows" and are tabulated at right, as extracted from the RFP.

What follows is an analysis of the far-reaching cost and schedule implications of Special Provision SP01040.

Temporal Windows

Special Provision SP01040 imposes the following time restrictions:
  • No work during weekday peak hours (6 - 10 AM and 4 - 8 PM)
  • No work on Tuesdays and Wednesdays overnight, for track maintenance
  • Only one track available mid-day, evenings and weekends
  • Two tracks will only be available in the early morning hours Friday - Tuesday.
The limits defined in SP01040 do not include time for sending crews and equipment to or from the work site, known in construction jargon as "mobilization" and "demobilization".  An hour is eaten away from the beginning and end of each work window for this purpose.

If you want to analyze a typical work week on an hour-by-hour basis, you can define six different track availability states.  Each state has associated to it an availability factor, which you can think of as how many tracks are available to perform productive work (i.e. re-signaling or constructing the overhead contact system).

Availability StateAvailability Factor
No access0
Mob/Demob for 1 track0
Mob/Demob for 2 tracks0
Single track available for work0.75
Mob/Demob for 2 tracks with 1 track already available1
Both tracks available for work2

During periods of mobilization or demobilization, the work window is technically open to the contractor, but no useful work can occur since crews are busy moving equipment and materials to/from the work site.  When a single track is available for work, trains passing on the other track will occasionally interrupt the work, which is why the availability factor is 0.75 rather than 1.  This typically accounts for 2 trains passing the work site every hour, causing work to cease for 15 minutes due to worker safety protocols.  When mobilizing both tracks for the contractor, these passing trains cease and the availability factor increases to 1.  The ideal situation is when both tracks are shut down and the contractor has full control of the work site.

Geographical Windows

The corridor has been divided into geographical segments, at least some of which must remain open at all times to allow northbound and southbound trains to meet and run past each other.  Each segment has a certain length (measured in route-miles).

SegmentLength (miles)
Segment #1, MP 0.3 - 8.0 (CP 4th to CP Sierra)7.7
Segment #2, MP 8.0 - 29.1 (CP Sierra to CP Alma)21.1
Segment #3, MP 29.1 - 44.5 (CP Alma to CP De La Cruz)14.8
Segment #4a, MP 44.5 - 47.5 (CP De La Cruz - CP Alameda)3.0
Segment #4b, MP 47.5 - 51.1 (CP Alameda - Tamien)3.6
Yard Facilities (4th & King, CEMOF, San Jose)3.0

Note that various yard facilities are assigned 3 route miles (6 track miles).

During the first phase of electrification, work may only occur in segments 2 and 4, with both tracks open in segments 1 and 3 to allow trains to meet.  Then, following an adjustment to the timetable, the second phase of the work will occur in segments 1 and 3, with both tracks open in segments 2 and 4 to allow trains to meet.  This allows Caltrain to maintain hourly service in both directions during mid-day, evening and weekend periods, single-tracking as needed around electrification work sites.

Labor Costs

Let us loosely define a unit of labor to perform electrification work on one mile of track for one hour (however many people that may actually take).  One labor unit is multiplied by the number of track miles and the number of hours to calculate a burn rate, or how much the labor will cost during any given period of time, assuming the contractor makes full use of the work windows.

We will assume that when both tracks are open, efficiencies can be realized so that only 1.5 labor units (rather than 2) are required to work on 1 route-mile (2 track-miles).  We can then assign a labor cost for each track availability state defined above:

Availability StateHourly Labor Rate
(per route mile)
No access0
Mob/Demob for 1 track1
Mob/Demob for 2 tracks1.5
Single track available for work1
Mob/Demob for 2 tracks with 1 track already available1.5
Both tracks available for work1.5

The work is performed by skilled union workers, whose hourly cost is not always the same.  While weekday work can be performed in shifts at no additional hourly expense, weekend work is another matter.  Depending on the union and the trade (the RFP contains hundreds of pages of union wage rate tables), weekend work can cost up to twice the rate of weekday work.  Let us assume overtime cost factors in as follows:

Day of WeekOvertime Factor
Monday - Friday1
Efficiency Metrics

Now let's pull all these assumptions together and come up with three metrics.
  1. The first metric is average track avaibility, measured in track-miles.  It measures how much of the railroad is available for actual productive electrification work, as opposed to shuffling workers and equipment or dodging out of the way of trains.  Average track availability is inversely proportional to how long it will take to complete the work.  If you double the amount of available track, the job can be done in half the number of weeks.  There are limits to this assumption, of course, but for sequential tasks requiring direct access to track, such as re-signaling and constructing the overhead contact system, this inverse relationship is quite reasonable.

    The way to compute average track availability is to assign each hour of the week a track availability state, based on the rules set out in SP01040.  Then, we multiply the availability factor (associated to that state) by the number of route-miles in that segment to calculate how many track-miles are available for work in that particular hour in that particular segment.  We can repeat this calculation for every hour of the week (24 x 7 = 168 hours) and for every segment.  Finally, we can add it all up and divide by the total number of hours in a week to figure how many miles of track are available on average.

    But it's not quite that simple.  Since the work is divided into two geographical phases, we must first add up the availability for segments 2 and 4 (Phase 1) and then separately add up the availability for segments 1 and 3 and the yards (Phase 2).  The average track availability for Phase 1 and Phase 2 is then averaged; this average is weighted by segment lengths to serve as a proxy for duration of each phase.
  2. The second metric is burn rate, measured in labor units per week.  It measures the rate at which money is spent on all the work, including not just actual productive electrification work but also the shuffling of workers and equipment and the dodging out of the way of trains.  This metric assumes that the contractor makes full use of the available windows, and that no additional hourly expenses are incurred outside of the work windows (e.g. due to the work not filling a full 8-hour union shift).

    The way to compute burn rate is to multiply the hourly labor rate (associated to each hour's track availability state) by the number of route-miles in that segment and the overtime factor for that particular day of the week, to calculate how many labor units are expended in that particular hour in that particular segment.  Once again, we need to be careful how we add up the labor for Phases 1 and 2, using the same partial sums and weighted averages as for track availability.
  3. The third metric is installation efficiency, measured in labor units per week per available track mile.  It measures how much of the labor is expended on actual productive electrification work, as opposed to unproductive tasks such as the shuffling of workers and equipment and the dodging out of the way of trains.  It serves a rough measure of the overall cost of tasks requiring access to the track, such as building the overhead contact system and re-signaling.  It is defined simply as burn rate divided by average track availability.  A lower number is better, indicating that a given length of track can be completed using less labor.
Four Scenarios

Armed with these metrics, we can analyze and compare a variety of electrification scenarios, including the baseline scenario specified in the RFP per Special Provision SP01040, and other scenarios of our choosing.

For the detailed calculations that support each scenario, or to explore your own scenarios and change any of the assumptions, you can download this Excel spreadsheet.
  1. Baseline Scenario: Let us scrupulously apply the work window restrictions from Caltrain's RFP, per SP01040.  Phase 1 has an average track availability of 13.3 track miles, while Phase 2 comes out to 12.1 track miles.  The weighted average of the two phases yields an average track availability of 12.7 track miles.  Bearing in mind that Caltrain has over 100 track miles to be electrified, this works out to a paltry ~12% of the railroad being available, a reflection of the extremely restrictive work windows.  This does not bode well for the program schedule, since having so little of the railroad available to the contractor will draw out the duration of all activities requiring access to the tracks.

    The burn rate works out to 3934 labor units per week, much of which is spent on mobilization and demobilization, as well as on weekend overtime work.

    The installation efficiency is 309 labor units per week per track mile.  When you consider that there are only 168 hours in a week, that is a terrible score indeed.
  2. Weekend Shutdown Scenario: One way to improve the average track availability is to completely shut down the railroad on weekends.  While this concentrates the majority of labor onto weekends when overtime rates are high, it opens up a 54-hour long period of uninterrupted access to segments 1 through 4a, while segment 4b and the yards remain partially open (to support tenant railroads and Caltrain maintenance activities).  This allows weekend work to be performed simultaneously in all segments, during both Phase 1 and Phase 2.

    Not surprisingly, average track availability improves considerably, with 35.3 track miles for Phase 1, 35.6 track miles for Phase 2, and a weighted average of 35.4 track miles.  By shutting down the railroad on weekends, we effectively tripled the amount of track access afforded to the contractor.

    The burn rate goes up quite a bit, because the entire railroad is being worked on every weekend.  The total works out to 8044 labor units per week.

    The installation efficiency is 227 labor units per week per track mile, a savings of 27%.
  3. Friday + Weekend Shutdown Scenario: The next possible step is to shut down the railroad on Fridays to extend the weekend work window to three days.  This has the advantage of increasing availability during a non-overtime weekday, but it is disruptive to riders who need to commute five days a week.  Weekend access increases from 54 hours to 78 hours, again with all four segments being worked simultaneously.

    Average track availability increases to 45.4 track miles.  Burn rate increases to 9144 labor units per week.  Installation efficiency improves to 201 labor units per week per track mile, a savings of 35%.
  4. Total Shutdown Scenario: The most draconian possibility is to shut down the railroad entirely.  It would be extremely disruptive for riders.  It could very well gridlock the highway 101 corridor, and in so doing, drive home the value of Caltrain for hundreds of thousands of commuters who never use Caltrain.  It would leave freight customers high and dry.  On the plus side, it would enable a coordinated construction "blitz" to complete the work at lower cost and far faster.  Electrification could even be combined with other projects such as grade separations.  Segment 4b and the yards would remain partially open (single-tracked) for the tenant railroads that use the southern end of the corridor.

    Average track availability would shoot up to 98.2 track miles.  Burn rate increases to 15600 labor units per week.  Installation efficiency improves to just 159 labor units per week per track mile, a savings of 49% (half off!)
Here are some graphs to summarize the results of this analysis.

You might wonder about the point of this exercise.  The RFP is closed and all the bids are in, so isn't all this overcome by events?

Word has it that the bids came in much higher than Caltrain expected, with contractors blaming the restrictive work windows for the higher cost.  Caltrain is now scrambling to scrape together even more funding than the $958M they thought electrification would cost (not including new vehicles).  Recall about half of that sum was estimated for re-signaling and building the overhead contact system, tasks where cost and schedule are strongly driven by work windows.

Shut Down This Railroad!

The right answer isn't to go digging between couch cushions for another several hundred million dollars.  The right answer is to shut down this railroad, because trying to electrify without shutting it down is like trying to change a flat tire without stopping your car.  A weekend shutdown would speed the work by a factor of nearly three, and reduce cost by about $150 million.  Shut down three days, save $200 million.  Shut everything down, save nearly $300 million.  Okay, maybe don't shut everything down, but at the very least, the weekends must go.

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?

13 November 2015

The U-Shaped Grade Separation

While some cities and towns on the peninsula are still holding out for trenches or tunnels to bury the railroad tracks out of sight, the astronomical cost and difficulty of constructing such structures below the water table in seismically unstable soils makes it likely that above-ground solutions will ultimately prevail, anywhere rail traffic needs to be separated from road traffic.  An attractive above-ground solution is the U-shaped grade separation.

What is a U-shaped grade separation?

U-shape bridge cross section, showing the benefits of
reduced track elevation
A U-shaped grade separation is a type of railroad bridge used to elevate the tracks above road traffic with as few community impacts as possible; there are no property takes and all road turning movements are preserved.  The bridge structure consists of sections made from two pre-stressed concrete side beams, forming the two sides of a U shape, connected by a flat slab forming the bottom of the U, on which the tracks are laid.  The side beams bear the bending loads from the weight of the bridge and the trains that it carries.  This is not a typical railroad bridge design; it is a specialized configuration used to quickly and efficiently build elevated urban metros in cities where these systems are being built from scratch in a densely built environment.  The concept is further explained in a paper and a patent.

While the peninsula rail corridor is not a new metro system, these U-shaped structures could still prove useful in a major push to grade-separate the 40 grade crossings that remain, enabling higher speeds and more train traffic while relieving road congestion and improving east-west access across the tracks.

What are the advantages of U-shaped grade separations?

U-shaped grade separations combine several attractive features that make them ideally suited for developed areas along the peninsula rail corridor, and certainly much better than the massive hollow core concrete box girder bridges considered standard issue by the HSR project as shown in the graphical comparison above.
  • Lower track elevation.  The U shape minimizes the depth of the structure (measured from the underside of the bridge span to the top of the rails) to 3 feet or less.  This allows the standard 16-foot road clearance to be provided by raising the tracks just 19 feet above the road surface, about 8 feet less than the large elevated concrete box-girder viaducts that were proposed during the 2010 Analysis of Alternatives for peninsula HSR.  The rails are lowered thanks to the U shape, which places the structural support of the bridge to the sides, rather than under the trains.
  • Lower visual impacts.  When the tracks don't need to rise as much, the rail approaches to a grade separation become correspondingly shorter and less obtrusive, impacting fewer views. The structures above rail level, such as overhead electrification poles, are also lowered.  This reduces the so-called "Berlin Wall" effect of a grade separation structure.
  • Lower train noise.  The side beams function as natural sound walls, trapping rail noise before it has a chance to escape into adjacent neighborhoods.  They are especially effective because they are thick and quite close to the train.  This obviates the need to add sound walls on top of the bridge, making the finished structure less visually obtrusive.
  • Better earthquake resistance.  The lower profile of the bridge structure reduces bending moments applied to the piers and foundations, whether by earthquake forces or train braking and acceleration or wind loads.  This makes the bridge piers less massive and integrates them better into the built environment.
  • Better station integration.  Where stations must be located on an elevated section, structures are simplified thanks to the lower profile of the track, which reduces the reach of stairs, ramps, escalators or elevators, making for a more passenger-friendly environment.  The side beams of a U-shaped viaduct have their top flange at the same height as the train floor and form the actual platform interface, 50 inches above the rail and 72 inches from the track center line, allowing the U-shaped structure to continue uninterrupted through the station.
  • Better safety in case of derailment.  The side beams are close to the train.  In case of a derailment, train cars will be guided by the structure and will not topple off the bridge.  This feature is known as "derailment containment."
  • Lower construction cost.  U-shaped elements can be prefabricated off-site and assembled with minimal disruption compared to traditional cast-in-place construction methods.  Using standardized elements throughout the corridor, in dozens of locations, provides economies of scale.  The decreased profile changes for both rail and road (whether the U-shaped bridge is elevated or at-grade with the road sunk underneath) require less excavation or fill.
The U-shaped design can minimize property takes, preserve turning movements for cars and trucks, cost much less to build than below-grade solutions, and tread more lightly through built-up neighborhoods than a conventional (box beam) viaduct or split-grade separation.  U-shaped bridges are ideal for grade separation in dense areas like the peninsula.