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.

26 August 2015

Level Boarding: It's Official

A montage of what a Caltrain EMU might
look like, before platforms are raised.
Based on a photo by Yevgeny Gromov
Caltrain just released the final Request For Proposals for their new electric train fleet.  Train manufacturers will now prepare detailed bid packages, and in early 2016 a winner will be selected to build an initial fleet of 15  electric trains that will enter into commuter service in 2021.

Several changes were made to this document after the draft RFP was circulated for industry review.  The single most remarkable change is that level boarding and platform sharing with high-speed rail is now a firm requirement, instead of an option suggested by stakeholders.  These are the words from section
CHSRA trains will run over the same alignment and stop at some of the same stations as JPB trains. The bi-level EMU must therefore have the same interface with the infrastructure as the future High Speed Rail cars, including clearance envelope, and platform boarding height.

JPB plans to raise platform heights to approximately 50.5-50.75” ATOR (to interface with a vehicle threshold height of 51” ATOR), initially at San Francisco, Millbrae, and San Jose stations. Other station platforms on the JPB system may ultimately be raised to the same level.
This is not only an endorsement of level boarding.  It is an endorsement of complete integration with high-speed rail including not just shared tracks but also shared stations.  It is a major step forward for riders and taxpayers, because it will increase the speed, efficiency and usability of Caltrain at the same time as it makes high-speed rail more affordable.  It will help bring to California what Europeans take for granted.

The New Platform Interface

Section 3.3.3 of the RFP details Caltrain's new high platform interface:
  • Platform height: 50.5 - 50.75 inches
  • Platform side clearance: 72 inches from track center line
  • Maximum boarding gap: < 1.5 inches horizontally, < 5/8 inches vertically
Caltrain has entirely dropped the previous plan to implement level boarding at a height of 25 inches, which would not have been compatible with high-speed rail and would have created significant complications in the station infrastructure served by both systems.

Dual Height Doors

The new EMUs will have two sets of doors, not just as an option but as a non-negotiable requirement.  The RFP describes the configuration in section 12:
Each vehicle shall have eight door openings, four on each side of the vehicle, directly across from each other. One set of four shall be located just inboard of the trucks and the other four above the trucks. The set located inboard of the trucks (the low level set) shall be compatible with JPB's existing platform height and existing mini-highs. The set located above the trucks (the high level set) shall be compatible with JPB's future high level platforms.
A large number of bikes (at an 8:1 ratio of seats to bikes) will be stored on the lower level of two cars per train.  They will access the high doors using wheel ramps built into the stairs between the lower bike level and mid level vestibule of the train.

While this is a rather unique configuration, no other train operator worldwide has had to plan for a system-wide platform height transition of more than four feet of vertical change.  For such a large height transition, it makes perfect sense to use the vehicles as a tool to enable the flexible and independent reconfiguration of each individual platform, without imposing system-wide construction schedule or funding constraints.  It is an unusual but quite logical solution to an unusual problem.

The upper set of doors, which will provide level boarding at new high platforms, will feature retractable door threshold extenders, to bridge the gap between the train and the platform.  These are described in section 12.2.12 of the RFP.

Looking Ahead to a Well-Blended System

Caltrain has come a long way on the issue of level boarding and blending with high-speed rail.  A key architectural decision has now been made that will ensure the future success of the blended system.  In the 2020s, Caltrain passengers of all abilities won't give a second thought to the seamless experience of boarding a train, and will take for granted the brevity and punctuality of station stops.  Meanwhile, a few train nerds will photograph the platform interface.

In the meantime, three cheers for compatibility!

08 August 2015

Peninsula HSR, Take Two

Environmental clearance of high-speed rail in the peninsula rail corridor was initiated right after the Proposition 1A bond passed in 2008.  The development of engineering and environmental documentation for a four-track alignment connecting San Francisco to San Jose was in full swing during the years 2009 and 2010.  The Peninsula Rail Program, as it became known, was an ambitious yet awkward collaboration between the CHSRA and Caltrain, with the engineering consulting firm HNTB doing most of the heavy lifting.  The decision to concentrate HSR resources in the Central Valley, combined with fierce community opposition on the peninsula, brought the process nearly to a halt in early 2011.  By that time, thousands of pages of documents had been drafted, hundreds of stakeholder meetings held, and $45 million spent for preliminary engineering and environmental clearance.

Then came a long pause during which two major developments took place.  First, as a result of a political compromise, the idea of a four-track high-speed railroad was dropped in favor of a "blended system" where Caltrain and HSR would share the peninsula corridor primarily on two tracks, with less impact to surrounding communities.  Second, the Caltrain electrification project came closer to being realized, passing key milestones of environmental clearance, funding, and procurement.  Throughout this pause, plans for peninsula HSR became somewhat nebulous, both in their scope and timing.  The media spotlight turned away.

Fast forward to the August 2015 meeting of the California High-Speed Rail Authority (YouTube video).  As reported by the Fresno Bee (and without a peep from the Bay Area press) we have the first hints of what lies ahead, in the form of a Request For Qualifications issued by the CHSRA to re-start the environmental clearance process for the peninsula.  This RFQ lays out a new timeline and a $36 million budget allocated over a term of three years, shared between two sections: San Francisco to San Jose, and San Jose across Pacheco Pass to the Central Valley wye.  The following schedule milestones are envisioned:
  • Consultant contract award - November 2015
  • Project scoping - March 2016
  • Preliminary design for project definition - May 2016
  • Technical reports - June 2016
  • Administrative draft EIR/EIS - August 2016
  • Draft EIR/EIS release - November 2016
  • Preliminary design of preferred alternative - April 2017
  • Final EIR/EIS certification - November/December 2017
The timeline for actual construction is not specified, but it rarely begins immediately after EIR certification, since final design and the inevitable CEQA lawsuits take time.

Highlights from the RFQ

The RFQ deliberately does not reveal the scope or exact nature of the alternatives to be studied, but it does contain some interesting nuggets:
  1. Work for restarting the peninsula HSR process has already started, as noted on PDF page 24: "Work on some of the tasks listed in Exhibit A of Attachment C has commenced and is currently being performed by Authority and Rail Delivery Partner staff."  What the blended system will look like is already being hammered out.
  2. The RFQ emphasizes that the proposed EIR is separate from Caltrain's electrification EIR, on PDF page 28: "On January 8, 2015, the JPB certified the PCEP Final EIR and is currently in the process of procuring a design/build contract to implement the project. While the PCEP will not include all infrastructure necessary to implement HSR service in the SF-CVY Corridor (such as HSR maintenance facilities, station platform improvements, track straightening, or passing tracks), the electrification infrastructure (such as overhead wire systems), along with additional infrastructure improvements, will accommodate future coordinated service and will not preclude HSR."  This point is the subject of a CEQA lawsuit against Caltrain, claiming that electrification is an inseparable component of the HSR project.
  3. Phased implementation is described on PDF page 57: "The Consultant shall develop an incremental plan as directed by the Authority to construct the project over a phased implementation schedule, dependent on funding. The Consultant shall recommend appropriate construction elements for each increment of implementation. This plan shall identify operable project segments or elements of the HSR infrastructure (such as grade separations) that could be constructed early and bring near-term project benefits to existing freight rail and conventional passenger rail services, as well as other increments of construction to build out the full set of improvements over a phased implementation plan."  The peninsula corridor is uniquely suited to a number of construction packages to be built independently from each other.
  4. San Jose is no longer an artificial boundary between two project sections.  This has been a weakness in the past, with insufficient coordination to optimize the configuration of the station and its approaches because each end was being handled by a different consultant.  With the same consultant handling both ends of San Jose, sanity may finally prevail with a shared at-grade solution.
  5. Level boarding planned for Caltrain, on PDF page 60: "Platform design for level boarding at all Caltrain stations will be required."  Even if not at the same height as selected for HSR, level boarding is a prerequisite for the blended system, to improve the average speed and punctuality of Caltrain.
  6. A temporary San Francisco terminal is planned at 4th and King.  The mere idea of it illustrates the frosty relationship between the CHSRA and San Francisco's TJPA, but also helps to satisfy the requirement for a 30-minute trip from San Francisco to San Jose, a threshold of great legal significance that is embedded in the Proposition 1A bond act.  Starting from 4th and King, rather than from the Transbay Transit Center, running at no more than 110 mph, and counting only pure run time (with no timetable margin), the 30-minute run becomes feasible.
EIR Cost Magnitudes

Environmental Impact Reports are extremely complex and voluminous documents designed to clear a project under the California Environmental Quality Act, ensuring that impacts are properly disclosed and mitigated.  It takes a large team of engineers, environmental specialists, writers and lawyers to concurrently design a project and pull together an EIR that can pass legal muster without incurring years of litigation.  To understand exactly where the process currently stands for peninsula HSR, it helps to remember that the published record for the San Francisco to San Jose project section forms only the tip of the iceberg.  The vast majority of the material assembled by HNTB in 2009 and 2010 remains unpublished, to be continued by this new contract.

How much EIR preparation did the $45 million spent so far buy?  We can establish an extremely crude metric for the cost of one EIR page by taking the ratio of the cumulative cost incurred for the preliminary design and environmental clearance of a project, as of the time of EIR certification, divided by the total number of pages in the resulting EIR.  Here are some examples:

Project Certification Cost Incurred Page Count Cost Per EIR Page
Merced - Fresno HSR May 2012 $45M 13,000 $3500
Fresno - Bakersfield HSR May 2014 $120M 20,000 $6000
Caltrain Electrification Jan 2015 $14M 5,400 $2600
Peninsula HSR SF - SJ Dec 2017 $65M* 13,000** $5000***

*cost basis $45M expended to date + $20M of the new $36M contract
**estimated based on cost per page
***estimated based on past history and biased high for scope change from full build to blended

Given that the new consultant won't be starting from scratch, it's conceivable that there will be sufficient budget in the new contract to produce a full EIR for the blended system on the compressed two-year timeline envisioned in the RFQ.

What the Blended System Might Look Like

The CHSRA and Caltrain take great pains to remind everyone that we won't know what the blended system for the 50+ mile peninsula corridor will look like, nor what the blended service plan will be, that is, until the Alternatives Analysis is released next year.  The specific discussions regarding the scope of the blended system are underway behind closed doors.  Taking into account the phased and incremental nature of the project, one can engage in some informed (wishful?) speculation, listed from north to south:
  • 4th and King shared station modifications.
  • Brisbane HSR maintenance facility.
  • Millbrae shared station modifications, hopefully with an affordable shared at-grade solution.
  • San Mateo County grade separation Phase II at Linden Ave in San Bruno, Center St in Millbrae, Broadway in Burlingame, and 25th / 28th / 31st in San Mateo.  The latter are likely to happen sooner than the other projects to enable the mid-line overtake.
  • Grade separation through highly constrained downtown San Mateo.
  • Four-track 110 mph mid-line overtake facility (from San Mateo 9th St, through Belmont and San Carlos, initially to Whipple in Redwood City).
  • Redwood City grade separation Phase IV, extending the four-track mid-line overtake through downtown, possibly with a new HSR station replacing the Sequoia Shopping Center, if the city and CHSRA agree to add this to the project scope.
  • PAMPA (Palo Alto Menlo Park Atherton) grade separations, likely to happen later than the other projects.
  • Santa Clara County grade separation Phase III at Charleston and Meadow in Palo Alto, Rengstorff and Castro in Mountain View, Mary and Sunnyvale Ave in Sunnyvale, creating a continuous 14-mile stretch of grade-separated track good for 110 mph from Palo Alto to San Jose.
  • San Jose approach realignment and a shared ground-level station.
  • A three-track at-grade alignment through San Jose's Gardiner neighborhood, along the existing right-of-way, avoiding a slow and expensive viaduct above the 87/280 interchange.
  • Curve flattening throughout the peninsula, except (unfortunately) in San Bruno
  • Level boarding across the entire Caltrain system, a key blending ingredient that ensures commuter trains can clear the shared tracks quickly and reliably in front of high-speed trains.
The next formal step in the process will be a new Notice of Preparation (NOP) to be published by the FRA in the Federal Register, an action that could come in the coming months.  Then we'll party like it's 2009.

18 July 2015

News Roundup, July 2015

Cost of Dual Height Boarding: with its industry review of the EMU draft RFP, Caltrain sought feedback from vehicle manufacturers regarding the cost and feasibility of delivering vehicles with dual boarding height capability.  According to the latest EMU procurement update, the feedback received indicates that vehicle cost would increase by just 3 to 5 percent.  This small premium (roughly $20 million) all but ensures that the HSR project will be able to pay for this important compatibility feature.

New Rules for Electrification: the California Public Utilities Commission has released General Order 176, the Rules for Overhead 25 kV Railroad Electrification Systems for a High-Speed Rail System.  The new GO, effective as of 26 March 2015, will also serve as the regulatory framework for Caltrain's electrification project, despite the peninsula corridor not qualifying as "high-speed rail" as narrowly defined in the document.  Three major issues remain to be hammered out with regulators and freight railroads: (1) grade crossing warning systems, (2) vertical clearances, and (3) freight personnel safety and training for operating freight trains in electrified territory.  These three issues are minor and unlikely to require a new rule-making process.  The release of GO 176 is timely for Caltrain's electrification project.

Cap and Trade Maneuvering: at least two lines of attack are being pursued by opponents of Caltrain electrification and the high-speed rail project.  First, there is or will be legal action that seeks to deny the use of Proposition 1A HSR bond funding to pay for Caltrain electrification, based on the (quite defensible) argument that electrification isn't high-speed rail and won't meet the legal restrictions of the bond measure. Prop 1A high-speed rail funding accounts for the lion's share of the funding package for electrification, a contribution of $600 million.  The underlying calculus is that denying this funding would kill the electrification project. Second, there is or will be legal action that seeks to deny the use of Cap and Trade funding to pay for high-speed rail, based on the (quite defensible) argument that the greenhouse gas reductions from HSR will only occur far in the future, well beyond the time frame required by CnT legislation.  Both of these legal challenges can be neutralized in one fell swoop, by substituting HSR CnT funds for the HSR Prop 1A funds. According to Caltrain's EIR, electrification will reduce greenhouse gas emissions by 80,000 metric tons per year initially, increasing to 190,000 metric tons by 2040, largely by cutting automobile traffic.  It doesn't get much more short-term than that, and CnT funds come with far fewer strings attached than Prop 1A funds.  Look for the funding swap to occur this fall, when the nine-party MOU is revised to reflect the growing electrification budget.

HSR Business Plan Machinations: due to the lack of funding to build the extremely expensive mountain crossings, there are indications that the 2016 business plan for HSR will call for service to begin in the SF and LA areas several years before the Central Valley is linked to anything.  This should be of some concern to Caltrain because it would put HSR in direct competition with Caltrain for affluent tech commuters, no matter what they say.  If Caltrain is elbowed out of the lucrative express market, the loss of revenue will be entirely HSR's gain.  While this Bay Area mini-HSR might show an operating profit (as required by law), it could only do so with a hidden subsidy, provided in the form of extremely scarce and valuable rush-hour track capacity.  Competition is great, but the market mechanisms for sharing the peninsula rail corridor "fairly" (whatever "fair" means to each stakeholder) would need to be carefully developed.  Then again, this silly idea might just wither on the vine, since the letters 'H' and 'S' would be absent from HSR.

14 June 2015


Caltrain recently published their Electric Multiple Unit (EMU) Request for Proposals (RFP) in draft form, to obtain feedback from potential proposers prior to the formal issue of this document in August 2015.  Here are some initial impressions:

What's Pleasantly Surprising:
  • Level boarding is a serious consideration throughout the RFP.  Caltrain appears to recognize the importance of this issue: it's the Next Big Thing after electrification, and cannot wait until the next round of vehicle replacement in the 2050s.  The RFP shows that Caltrain is starting to walk the walk, not just talk the talk.
  • Platform sharing and full blending with high-speed rail is firmly on the agenda with "Option B," a dual boarding height train that enables an eventual transition to level boarding at 48 - 51" height.  This solution has been described and advocated on this blog as the best one available given the constraints of the problem.  Most people who reject this solution ultimately take issue with one of the constraints, but once you accept these constraints, "Option B" starts to make more sense.  Proposers are asked in the draft RFP to further evaluate its feasibility and cost impact.
  • In section 3.3.3, future capability for level boarding is described as ADA-compliant with a 3-inch maximum horizontal gap and a 5/8-inch maximum height mismatch.  Section 4.2.3 specifies a pneumatic leveling suspension to meet the vertical tolerance. It looks like Caltrain  is going the extra inch after all, which is commendable.
  • The vehicle static envelope in Appendix C is a full 3.4 meters wide, enabling the use of extra-wide trains, wider than the conventional AAR plates.  While Caltrain doesn't seem keen on 3+2 seating (something about the "middle seat" situation), extra width that takes full advantage of the static envelope is good for all uses besides seating.  Let's hope the proposers aren't timid about this.
  • While it isn't immediately obvious from looking at the raw numbers, the run times required in section are fairly aggressive and will require some sporty power-to-weight ratios.  This high level of acceleration and braking performance is good for the blended system and will ensure that the most can be made of shared tracks.
  • In section, door controls are required to be installed in the driving cab, offering the possibility of consolidating and automating a task currently performed by conductors.
  • In section 14.4, an automatic station announcement system is specified to automate a task currently performed by conductors.  This isn't exactly surprising for a modern train, but Caltrain and its labor practices sometimes seem stuck back in the 20th century.
  • In section 14.9, the trains are required to be pre-wired (if not yet equipped) for passenger Wi-Fi.  For a rail system that serves Silicon Valley, that's overdue by easily a decade.
  • No trap doors!  That always seemed like a horrible way to achieve level boarding.
What's Disappointing:
  • The RFP is highly prescriptive.  The cost of preparing such a voluminous requirements specification, and then to formally verify such a large number of requirements, will easily run into the millions of dollars.  So much for off-the-shelf procurement.
  • In section 2, no allowance is made for articulated trains (e.g. Bombardier Omneo) or for trains with mixed bi-level and single level arrangements (e.g. Siemens Desiro HC).  The desired EMU is prescribed as a set of traditional bilevel cars each about 85 feet long.  A better approach would be to define a minimum passenger capacity per unit length, leaving more room for creative and unconventional interior layouts.
  • Still no detailed thought appears to have gone into how to transition to level boarding under "Option A".  The height of 24 or 25 inches is intended to match Caltrain's existing Bombardier bilevel cars, which is a bit mystifying since there is no feasible transition to level boarding using these cars.  Section 3.3.3 basically asks for proposers to figure it out for Caltrain: "Heights below 24 inches will be considered for future level boarding if the Contractor can demonstrate conclusively that the height is advantageous for JPB’s envisioned service and compatible during the transition to that envisioned service."
  • Section 12 requires all doors of the train to open at every stop, as they do today.  To reduce wear and tear on the door mechanisms, modern vehicles often come equipped with interior and exterior push buttons for passengers to initiate door opening.  Instead of opening the doors by default, the crew-operated door control station should de-inhibit the doors to be opened only as requested by passengers at each individual door.
  • Section 2 envisions that trains would be lengthened from 6 cars (~150 m) to 8 cars (~200 m) at some future date.  This is far too timid a capacity expansion.  A more flexible and future-proof approach would be to order more 150 m trains and double them up-- after the necessary platform extensions are constructed at stations with the highest ridership.
What's Weird:
  • Section 2 requires shorter 6-car trains to have their performance de-rated (by software) to the same performance as a longer 8-car train.
  • Section 23.2.2 requires the delivery of 200 (two hundred!) 1/50th scale models of each car type for "internal and external distribution"... That's some serious schwag!
What's Missing:
  • "Option B" with dual boarding levels requires level boarding at 48 to 51 inches ATOR but fails to describe the basic platform interface dimensions, including height above rail, offset from track center, and tolerances thereon.  Proposers are unlikely to be able to design against such a critical interface when it hasn't even been defined.  This data should be agreed upon with the California HSR Authority, after some technical decision making that may have to occur sooner than they would like.
  • In section 3.3.3, Caltrain requires that "the entire platform interface system must also be usable during the transition from the current platform height to the level boarding platform height," a stealth requirement that makes "Option A" trains at least as mechanically complex as the "Option B" trains, by requiring boarding capability at two different heights (8-inch legacy and 25 inches with ADA-compliant level boarding).  A requirement of such great importance and design impact ought to be made more explicit, saying what it actually means and using the word "shall".
  • The door control system (section 12) envisions 100% manual operation of the doors by train crews.  This may not properly address the challenge of operating during a platform height transition, when each individual platform may need to be raised in successive construction phases to avoid closing the station or doubling the construction footprint for temporary platforms.  With manual door operation, the risk of human error resulting in opening a door at the wrong platform height will likely be unacceptable, particularly to regulators such as the CPUC.  It may be warranted, at the cost of some additional complexity, to require a platform sensing system that automatically inhibits door opening when the incorrect height is sensed, preventing crew errors and potential passenger injury.
Please use the comment section to add your own review of this document.