Printer-friendly version

HatTrench   Drawings:         

aka : Dual Stack Cut & Cover Trench/Tunnel

• Unites Communities: Allows for reuse of space over CalTrain/Freight/High Speed Rail. Cities can reclaim this space, bringing their communities together. Image: parks, streams, bike paths, roads, buildings, light rail...
• Improves Quality of Life: Properties adjacent to tracks may be transformed. CalTrain/Freight/High Speed Rail - don't see it, don't hear it, don't feel it (well, at least for many properties)
• Allows for Civic Imagination: Add keystones in the future, which may be shipped to the site in a standard sized 40 foot container.

Versus: Most of the other alternatives, including Deep Bore Tunnels, which keeps CalTrain/Freight above grade.

But: At what cost? Although the early estimates for this option seem to indicate a large price tag, what about:

• Eminent Domain: Other options, including At-Grade, excluded the cost of Eminent Domain in their estimates, which this option's minimized Right-of-Way profile may mitigate.
• Lawsuits: This option has the potential of creating a net benefit to property owners next to the tracks. Although litigation is a certainty for a project of this size, many property owners may actually see their values increase after construction. Track becomes a Park - Yes!
• Delay: This option generates value to the local communities, which in turns could minimize city driven delay tactics.
• Check the Numbers: CHSRA cost estimates were very early and understandably a bit raw. 
  • Aerial options (aka "structure") seems to use the same estimate for two-tracks and four-tracks. 
  • At-Grade, with about a 1000 foot impact area (up and down sloping of streets), did not include property taking and city reconfiguration. 
  • Covered Trench seems to be more than double Open Trench costs. Great time to be in the Tench Cap business...hummmm.
    • Hatch Mott MacDonald (HMM) report to Palo Alto (CMR 255:10) "Cut and Cover costs appear excessively high...no explanation is given (in the Alternatives Analysis Report) which explains why the Cut and Cover option is over twice as expensive as the U-Trench which is essentially the same construction absent a structural cover. The U-Trench costs $190 million per mile compared to $486 million per mile for the Cut and Cover option." City of Palo Alto, City Manager's Report, May 19, 2010, CMR: 255:10, Page 2.

Assumptions to Challenge:

• CalTrains Operations: Could we operate Freight/CalTrain on a single shoo-fly track, with two tracks at the stations, during construction?
• Four Tracks versus Two Tracks: Are four tracks actually necessary? Can CalTrain/Freight/HSR share two tracks, with four tracks at stations? Using a HatTrench design, can we built the upper Trench/Tunnel in a phase one, with the lower Tunnel built in the future? Alternatively, if Right-of-Way permits, a second set of tracks, inside a trench/tunnel could be build next to the phase one Trench/tunnel at a later date.
• Shared Baby Bullets: Cannot the High-Speed Train be our Baby Bullet, stopping in San Jose, one other current CalTrain station, then onto BART/SF.
• Tench Caps: Design trench for low cost future capping. CHSRA builds trench and current crossings (roads, utilities, streams...). Cities are given aerial rights above grade. Cities add Trench Caps in the future, on a project by project basis and when funds are available.
• Peninsula BART: Built two-track, cut & cover trench/tunnel now (HatTrench) on the top section, then use the bottom tunnel for BART. A two-track subway box for BART has a cross section of about 40 x 20 feet. This means the bottom box could be smaller than the top box, making second phased future construction a bit easier. BART then helps cities pay for Trench Caps.

Result: If HatTrench + Single Shoo-fly Track + Phased build w/Two Tracks + Shared Baby Bullet = Potential Benefits: Narrow Right-of-Way Impacts + Decreased HSR cost + Lower Operational Cost to CalTrain + Reunites our Cities + Increased Property Values (we hope)

Please see: HatTrench Concept Drawing    

Please see: HatTrench in Alternatives Analysis  

While we are in support of the HSR project, we are sensitive to the potential impact of HSR in terms of noise, visual quality & aesthetics, community impacts, cost and long term flood hazards. In the spirit of creative civic imagination and to best address these issues we recommend that the CHSRA investigate an alternative, which we call a HatTrench (Hybrid, Adaptive and Tiered Trench). A HatTrench is a two-level tunnel with the lower tier dedicated to HSR and Baby Bullet, and the upper tier for local CalTrain and freight. The top of the upper tier, which is open to the air, may be fitted with various keystones (an arched cap). These keystones may be mass customized according to need (air exchange/security, street bridge, walking/bike bridge, light rail right-of-way, leasing of air-rights, stream crossing...).

A Little Civic Imagination

As we studied the various classic grading implementations, we found weaknesses in each alternative. An above-grade 4 track system, at-grade and a traditional below-grade trench would have the impact of dividing our community due to walls, fencing and trench gaps. A traditional tunneling alternative will most likely prove too costly. Furthermore, potential sea level rise across the next two centuries means adaptivity must be incorporated into any design.

From a requirements' perspective, the question is which design would be quiet, provide a low visual profile, allow for venting of diesel exhaust (freight, local CalTrain), require minimal or no community barriers (fencing, walls, wide trench), minimizes loss of private property via eminent domain and can be sealed at some future date to protect against flood? We support investigating a solution that combines a tunnel and a trench into a single unit, a HatTrench.

+ =

Trench (Reno)                         Tunnel (metro)                         HatTrench

Keystones (aka Trench Caps)

The tunnel top may be open to allow for proper venting of exhaust. To maintain structural integrity this top is replaced with a structural arch/vent to act as a keystone. This vent keystone may then act as a structured backplane which may be then adapted to provide site specific requirements, such as road, bike and pedestrian crossings, right-of-way for light rail or as a foundation for buildings which are granted air-rights. Central fabrication and mass customization of keystones would allow for faster and more cost effective built-outs. The Hat (keystone) is kept to a length of less than 40 feet, thus allowing for intermodal transport (ship, truck, rail), thus allowing for diversification of suppliers, thus pushing the price per unit down. If sea levels rise, the upper tier may be caped with a sealed keystone, thus converting the HAT Trench into a dual tunnel design.

The HatTrench provides a viable solution to many of the challenges for a grading strategy for the SJ-to-SF segment. We encourage CHSRA to invest design and engineering resources to properly investigate this option. We believe it may provide a viable cost effective alternative to more traditional grading strategies, protect the long term investment by providing an adaptive design, while meeting the needs of the local communities in terms of noise abatement and minimized visual impacts. Finally, a HAT Trench design unites rather than divides our communities.

Shared Tracks: Why Not Two Tracks?

At the request of OCTA (Orange County Transportation Authority) and the Los Angeles County Metropolitan Transportation Authority (Metro), a Shared Track alternative will be revisited for the Anaheim to Los Angeles segment. [Letter Attached below: OCTA/Metro to HSR Shared Track Request ] Why not a shared CalTrain/Freight/HSR track for the Peninsula, with only Two Tracks being built at this time, with an additional set built at a later date?

Benefits of a Shared Two-Track Strategy

• Lower construction costs.
• Shared operational/maintenance costs.
• Rationalization of passenger service.
• Opens mixed use of HSR for San Jose, local station (Redwood City, Mountain View, Palo Alto...) to San Francisco.
• Mitigates impact on communities (eminent domain)
• Makes alternatives more cost effective.

Brief History of HatTrench

• Early 2009: Submitted HatTrench concept as part of formal comments. 4/6/2009 Page I-SM-97 [big 100+MB file][ http://www.cahighspeedrail.ca.gov/images/chsr/20090626175642_I2_ScopingComments_Indiv_SM.pdf ]
• June 2009: California High-Speed Train: Draft Scoping Report for the San Jose to San Francisco High-Speed Train Project-Level EIR/EIS: June 2009 - Topic: Other: Page 66 “The Hat trench concept and a Maglev alternative should be explored” [Wow, up there with Maglev]

• June 2009: San Francisco to San Jose Section: California High-Speed Train EIR/EIS Apendix E.  Scoping Comments Disposition Table: Page E-4: Vertrical Alignment Options: Configuration of Below-Grade Alignment: “Use two tier tunnel (HST & Baby Bullet lower, local and freight upper), where the upper tier may be open to the air, in a Hat trench” Disposition: Included in Alternative Analysis

• Alternatives Analysis, Appendix C: See Attached Below

Dimensions, Details and other Specifics

The diagram is a sketch, which leaves a lot to your imagination and your own invention. Should the walls be concave or straight? Is a central support needed on the lower tunnel? What are the specific dimensions? How can this be constructed using the current ROW (Right of Way)? What about the need for a shoofly during construction? What is the construction foot print? Below is a sample of some of the discussions needed to work through these issues.

Source: http://cahsr.blogspot.com/2009/05/how-does-redwood-city-define-hsr.html

Clem said...

What would the dimensions of the HatTrench be? That's not too hard to figure out. It's driven by (a) vertical clearance requirements, and (b) tunnel cross section requirements, for aerodynamic reasons.

(a) for lower-story HSR, built to the shorter European UIC loading gauge, you need about 17 feet from top of rail to the overhead wire. Add another 4 feet of clearance from the high voltage wire to the tunnel ceiling. Under all that, assume about 6 feet of tunnel wall, track bed, and the track itself. Above all that, assume 5 feet of deck + track bed thickness to support the heavy trains above on the second story.

(b) To run trains in opposing directions at closing velocities of 250 mph, you need some aerodynamic buffer space both for vehicle stability and passenger comfort. Two-track tunnel sections would need about 80 to 100 m2 (800 to 1000 square feet) of open-air cross sectional area for 125 mph operation. That is probably a far more stringent constraint than (a) and may drive the height of the "downstairs" tunnel higher than I first described.

Then, above all that, add AAR Plate H or K clearance for freight trains (20 feet), and about another 10 feet of catenary poles and wires.

The depth of such a structure would be at least 50 feet from the top of a freight train (assumed level with the surrounding grade) to the bottom of the foundation. Wires and poles would stick up another 10 feet above ground.

Then, add the complication of ventilation and passenger evacuation. Then add the complication of periodically connecting the two levels so trains on the lower level can access stations (or do you double-deck stations too?)

In the end, the Hat Trench sounds an awful lot like this. But hey, kudos for trying to come up with solutions!

Direct Link to Comment >> May 19, 2009 10:17 PM

Pros and Cons Summary

• Low Sound Profile:  Sound from local CalTrain and freight are partially reflected back into the trench, with some sound being reflected skyward at a high angle.
• Low Visual Profile: As the Hat Trench is below grade, line-of-site impacts are small. A small footprint of the opening (keystone) will be seen when crossing over via a bridge.
• Narrow Profile: With two tracks stacked on top of each other the width is much less then the four track (~75 foot) alternative.
  • Preserves existing homes and buildings.
  • Minimizes need to cut down existing trees.
  • Mitigates impacts to existing rail stations.
• Lowers Cost
  • Decreased cost for acquisition of eminent domain rights.
  • Ability to recoup some cost via sale of air-rights (right to build on top of a right-of-way.
  • Lower cost build-outs, due to off-site central construction of keystones (top of the trench).
  • Lower cost relative to a tunneling solution.
  • Lower cost for bridges (road, bike, pedestrian) gives communities greater flexibility.
• Unites our Cities
  • Increases the number of rail crossings.
  • Replaces current above grade walls (think Belmont).
• Costs versus Alternatives: Construction cost differences against at-grade or above-grade still need to be determined.
• Some Added Costs:
  • Cost to move underground utilities under current CalTrain tracks.
  • Environmental issues surrounding any trenching operation.
• Adaptability: If sea levels rise, investment is secured, as future generations may cap the tunnel, forming a dual tunnel design, if necessary.
• Unites: Decreases division of cities by moats, gates or walls, while providing more opportunities to construct buildings and bridges across the current CalTrain right-of-way.
• Risks
  • Construction Footprint: Although the final width of the HatTrench may mitigate impact to nearby buildings, during the build-out accommodations may be needed if CalTrain/freight continues service.
  • For a comprehensive list of issues surrounding 'cut and cover' construction, please see: Table 2 here http://www.arup.com/_assets/_download/download235.pdf