HomeMy WebLinkAbout2026-03-10 Rail Committee Agenda PacketRAIL COMMITTEE
Regular Meeting
Tuesday, March 10, 2026
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VERBAL UPDATE ON INTERAGENCY ACTIVITIES
A.Caltrain
B.VTA
C.City Staff
STUDY SESSION
1.Review structural and design considerations for the Earthen Berm (retaining walls) and
long-bridge (Podium) options of the Meadow Drive Grade Separation Hybrid Alternative.
FUTURE MEETINGS AND AGENDAS
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ADJOURNMENT
2 March 10, 2026
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4 March 10, 2026
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Rail Committee
Staff Report
From: City Manager
Report Type: STUDY SESSION
Lead Department: Transportation
Meeting Date: March 10, 2026
Report #:2603-6052
TITLE
Review structural and design considerations for the Earthen Berm (retaining walls) and long-
bridge (Podium) options of the Meadow Drive Grade Separation Hybrid Alternative.
RECOMMENDATION
Review and provide feedback to staff on structural and design considerations for the Meadow
Drive Hybrid Earthen Berm (retaining walls) and long bridge (Podium).
EXECUTIVE SUMMARY
On December 15, 2025, City Council directed staff to explore an Earthen Berm and Podium-style
Hybrid alternative for Meadow Drive grade separation. Caltrain evaluated these structural
variants and considered various components including structural systems, construction
challenges, maintenance requirements, implications for future Caltrain operations, and
qualitative cost factors for each alternative. This study session presents an analysis and seeks
feedback from the Rail Committee in advancing the design of alternatives.
BACKGROUND
The City of Palo Alto is pursuing a grade separation project at three existing at-grade crossings at
Charleston Road, Meadow Drive and Churchill Avenue. Caltrain is leading the current Preliminary
Engineering and Environmental Documentation phase of the project, with the City as project
sponsor. Preliminary Engineering Conceptual Refinement (15% Design) is anticipated to progress
through Summer-2026, followed by Preliminary Engineering (35% Design) and Environmental
Documentation under the California Environmental Quality Act (CEQA) and the National
Environmental Policy Act (NEPA), which is anticipated to conclude in Fall 2027.
On September 16, 2025, Rail Committee reviewed refined concepts that had been developed to
minimize private property impacts while maintaining and/or improving the traffic circulation and
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enhancing pedestrian and bicycle crossings. On December 15, 2025, City Council (Staff Report
2506-4895)1 directed the project team to continue to advance the following alternatives:
Churchill Avenue Partial Underpass Alternative:
o Partial Underpass at Churchill without a landscaping strip
o Pedestrian/Bicycle Undercrossing at Seale Avenue using Alma Street ramp and
with attention to bicycle safety on the east side
Meadow Drive Hybrid Alternative
o Explore both an earthen berm and podium-style Hybrid alternative
Charleston Road Underpass alternative
o Underpass with Direct Access Ramp
ANALYSIS
Foundations: An Earthen Beam system requires MSE embankment walls that support the
soil and a short bridge segment that transfers load through supporting elements to deep
pile foundations and the soil. By comparison, a Podium system would require a concrete
superstructure that is generally more complex.
Settlement: Earthen Berms are subject to short- and long-term settlement, with potential
differential settlement across various segments or between the embankment and bridge
1 City Council, December 15, 2025; Item 26, Action Item, SR# 2506-4895
https://recordsportal.paloalto.gov/WebLink/DocView.aspx?id=84076&dbid=0&repo=PaloAlto
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abutments. Therefore, to maintain rail operations, track performance monitoring is needed, and
tamping and re-leveling of track could be expected. For the Podium system, minimal total and
differential settlement is expected.
Construction Impacts: The construction sequence for Earthen Berm requires a relatively
large footprint compared to other retaining systems. By comparison, the Podium variant
generally provides for better constructability in constrained corridors, especially when
utilities are present. Transition zones for the Podium system require special detailing and
enhanced maintenance.
Future widening: Widening of an Earthen Berm system is less challenging and less
expensive than a Podium. In addition, the Earthen Berm system is more adaptable to
accommodating additional tracks, signal upgrades and electrification upgrades. By
comparison, widening of a Podium system is more challenging and more expensive.
Costs: Upfront and lifecycle costs are expected to be lower for an Earthen Berm compared
to a Podium system. Qualitative structural cost implications of each system are listed
below.
Table 1: Structural Cost Implications for Earthen Berm and Podium Variants
Aspect MSE Walls (Earthen Berm)Long Bridge (Podium)
FISCAL/RESOURCE IMPACT
3
3 City Council, December 9, 2024; Item 12, Consent Item, SR# 2408-3322
https://recordsportal.paloalto.gov/WebLink/DocView.aspx?id=6521&dbid=0&repo=PaloAlto
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24000 (Meadow Drive and Charleston Road) and PL-24001 (Churchill Avenue Rail Grade
Separation and Safety Improvements). The secured $20 million is programmed to cover the costs
of the current 15% design phase as well as the subsequent 35% Preliminary Engineering and
Environmental Documentation.
STAKEHOLDER ENGAGEMENT
ENVIRONMENTAL REVIEW
ATTACHMENTS
APPROVED BY:
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Caltrain Palo Alto Grade Separation Project
Memorandum: Evaluation of Structural Alternatives for
Meadow Drive/Alma Street Grade Separation
Date: 03/04/2026
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Attachment A -
Memorandum Evaluation of
Structural Alternatives for
Meadow DriveAlma Street
Grade Separation
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1
Contents
List of Figures ............................................................................................................... 1
List of Tables ................................................................................................................. 1
1. Introduction ........................................................................................................... 2
2. Project Context and Requirements .......................................................................... 2
3. Structural Options .................................................................................................. 3
3.1. Alternative 1: “Earthen Berm” ........................................................................... 3
3.2. Alternative 2: “Long Bridge (podium)” ............................................................... 6
4. Structural Cost Implications (Qualitative) ................................................................ 8
List of Figures
Figure 1 - Existing site exploration at Meadow Drive ......................................................... 3
Figure 2 – 3D view of Caltrain corridor at Meadow Drive .................................................... 4
Figure 3 – Elevation view of railroad bridge at Meadow Drive ............................................. 4
Figure 4 – Elevation view of Earthen berm option ............................................................. 5
Figure 5 – Elevation view of long bridge (podium) ............................................................. 7
List of Tables
Table 1 – Qualitative cost implications ............................................................................ 8
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Memorandum Evaluation of
Structural Alternatives for
Meadow DriveAlma Street
Grade Separation
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1. Introduction
This memorandum provides a summarized technical evaluation of the two structural
alternatives for the hybrid underpass at Meadow Drive and Alma Street in Caltrain Palo Alto
Grade Separation (PAGS) Project. The analysis considers structural systems, construction
challenges, maintenance requirements, implications for future Caltrain operations, and
qualitative cost factors for each alternative.
For this evaluation, it is assumed that the removal and reinstallation of track systems and
traction power components will have comparable impacts for both alternatives.
2. Project Context and Requirements
The project involves raising the existing Caltrain track profile 16ft (max) over a distance of
approximately 6,400-ft, from Greenmeadow Way to Loma Verde Avenue. All existing
components of electrified tracks including Overhead Contact System (OCS), fiber lines and
other utilities, and power housing will be removed and reinstalled at a higher elevation to
maintain track operation. The design will need to provide flexibility for future widening of the
elevated segment within the Caltrain Right-of-way (ROW) to accommodate future Caltrain
operation and maintenance.
Approximately 7 ft of excavation is anticipated at the roadway crossings along Meadow Drive
to provide sufficient vertical clearance for the undercrossing and to connect east and west
sides of Caltrain corridor for the use of vehicles, pedestrians, and cyclists.
Although geotechnical study is still in progress, the preliminary indications suggest generally
favorable subsurface conditions, with no critical hazards identified, such as loose soils,
shallow groundwater table, liquefaction risk, or fault rupture within the footprint of the
structure. However, these conditions are to be further confirmed as additional geotechnical
information is available.
Existing underground utilities - including storm drain, sanitary sewer, water line, gas line,
fiber optic lines, and electrical lines – are present along both sides of the corridor.
Two structural alternatives are under consideration:
1- Short-span bridge over Meadow Drive with embankments enclosed by MSE walls,
referred to as the “Earthen berm”.
2- Continuous long bridge (podium) supporting the raised track profile.
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Memorandum Evaluation of
Structural Alternatives for
Meadow DriveAlma Street
Grade Separation
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This report focuses primarily on the structural evaluation of the alternatives, while also
considering construction logistics, durability, and cost implications as they relate to
structural design.
Figure 1 - Existing site exploration at Meadow Drive
3. Structural Options
3.1. Alternative 1: “Earthen Berm”
The Earthen Berm system consists of a reinforced soil embankment that supports the longer
portion of the raised track, along with a short, three-span bridge over the Meadow Drive
undercrossing to provide 16 ft–6 in minimum vertical clearance under the new railroad
bridge. The project involves raising the existing Caltrain track profile 16 ft (max) for a distance
of approximately 6,400 ft to eliminate at-grade crossings and improve mobility and safety.
The addition of soil mass at Caltrain corridor requires evaluation of extra excavation in the
next design phases.
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Structural Alternatives for
Meadow DriveAlma Street
Grade Separation
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Figure 2 – 3D view of Caltrain corridor at Meadow Drive
Figure 3 – Elevation view of railroad bridge at Meadow Drive
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Memorandum Evaluation of
Structural Alternatives for
Meadow DriveAlma Street
Grade Separation
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Figure 4 – Elevation view of Earthen berm option
For the embankment segment, the train loads would be transferred to the tracks and to the
embankment fill, MSE reinforcements, and supporting soil. For the short bridge segment,
the loads would be transferred through the middle bents and abutments (supporting
elements) to the deep pile foundations and the soil.
Two structural behaviors are utilized (1) the flexible embankment-supported tracks, (2) the
rigid bridge superstructure at Meadow Drive.
MSE wall embankment is typically compacted on native subgrade with facial panels
supported on shallow foundations; however, the bridge substructure will require deep
foundations, particularly if differential settlement tolerance is limited.
As mentioned in the previous section, MSE embankments are subject to short-term and
long-term settlement; and potential differential settlement at various segments of corridor
or between embankment and bridge abutments can be expected. Therefore, to maintain rail
operations and ensure track performance, tamping and re-leveling of track is expected. In
addition, transition zone performance should be monitored closely as approach slabs are in
the highest maintenance zone.
MSE walls perform well under seismic loading when properly designed; however, post-
earthquake serviceability may require embankment regrading or track adjustment. Track
operation is sensitive to rail alignment changes. Any potential soil mass movements under
the design earthquake may disrupt the operation of tracks.
The construction sequence of MSE wall embankment inherently requires a relatively large
footprint compared to many other retaining systems. In typical practice, the reinforcement
length ranges from approximately 0.7H to 1.0H (where H is the wall height), resulting in a
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Structural Alternatives for
Meadow DriveAlma Street
Grade Separation
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substantial horizontal zone of influence. This reinforced soil mass must be constructed and
compacted in layers, generally in 8- to 12-inch loose lifts, in accordance with project
specifications and standard compaction requirements (often 90–95% of maximum dry
density per ASTM D1557).
Because MSE wall construction progresses from the bottom up, each lift of structural
backfill requires placement, spreading, moisture conditioning, and compaction using
vibratory rollers or plate compactors. The operation of this heavy compaction equipment
induces dynamic loads and vibrations that may adversely affect nearby utilities, particularly
the aging shallow-buried pipelines or conduits.
Drainage performance is a critical design consideration for the long-term reliability of the
MSE wall system and should be carefully evaluated during both design and construction and
closely monitored after completion. The reinforcement corrosion protection is critical for
long-term performance and is closely tied to the effectiveness of the drainage system.
Internal drainage elements must be designed to minimize clogging risk and mai ntain long-
term permeability, while surface water management should prevent ponding behind panels
that could increase hydrostatic pressure and accelerate corrosion of reinforcements. The
system should also provide accessible inspection points for drainage outlets and collection
features to support routine maintenance. Ongoing post-construction monitoring of drainage
behavior is essential to confirm proper function and to identify early signs of blockage or
distress before they affect structural performance.
The widening of this system is less challenging and less expensive compared to next
alternative as the widening would happen within the isolated Caltrain’s ROW. In addition,
this system is greatly adaptable in accommodating additional tracks, signal upgrades, and
electrifications upgrades.
The track electrification components shall be removed and reinstalled in this alternative.
3.2. Alternative 2: “Long Bridge (podium)”
Under the Long Bridge system, approximately 490 ft of the raised track (5 spans) may be
constructed on a continuous, long bridge (podium). The superstructure may consist of
concrete systems such as a cast-in-place slab on precast/prestressed concrete girders,
precast/prestressed side-by-side box girders, or cast-in-place/post-tensioned concrete box
girders, or equivalent steel girder alternatives that provide similar structural depth and
constructability. More complex structural systems - such as steel through-girders, truss
bridges, or architecturally constrained configurations - are discouraged because they
complicate future widening, track additions, and corridor expansion. Simpler girder-type
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Grade Separation
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systems provide greater flexibility for staged construction and long-term modifications
within the Caltrain right-of-way.
Figure 5 – Elevation view of long bridge (podium)
The track loads would be transferred to the superstructure, bent caps, columns, and Cast-
In-Drilled-Hole (CIDH) pile foundations, and soil. This configuration offers a uniform
structural system with repetitive spans and consistent stiffness in the vertical and lateral
directions.
This system requires multiple columns and deep foundations (CIDH piles) at each bent.
Long bridge structures experience minimal total settlement and are less likely to experience
differential settlement affecting track geometry.
The seismic forces are carried through well-defined structural components (Superstructure,
bearings, columns, and foundations). The displacement-based seismic design can be
effectively implemented; and an easier post-event inspection and repair of discrete
structural elements can be carried out. In general, long bridges provide predictable seismic
behavior and clearer inspection and repair pathways. In contrast, to provide uniform
stiffness along the frames and reduce the likelihood of out-of-phase behavior of adjacent
frames, the need for isolation casing to extend the effective length of columns and provide
uniform mass to stiffness ratio along the long bridge makes the design and maintenance of
the bridges more complex.
Long bridge (podium) system generally provides better constructability in constrained
corridors, especially with utilities present. The transition zones require special detailing and
enhanced maintenance attention as mentioned for previous alternative. Higher likelihood of
long-term track settlement and geometry corrections exists. This system reduces ballast
maintenance and provides superior ride quality and long-term serviceability. By employing
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Structural Alternatives for
Meadow DriveAlma Street
Grade Separation
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direct fixation track, the ballast and its associated weight can be eliminated, further reducing
maintenance needs and allowing for a more compact, durable track structure. This
approach also improves track geometry stability and alignment over time, enhancing overall
operational reliability. Eliminating the ballast would significantly reduce the demands on all
components under service, strength, and seismic limit states.
The reinforced concrete bridge components have well-understood durability
characteristics, and individual components (bearings, joints) can be replaced. Longer
design life with predictable inspection and maintenance regimes is expected for this
alternative. Thus, this alternative offers lower long-term risk despite higher initial complexity.
The widening of this system is more challenging and more expensive compared to previous
alternative.
The track electrification components shall be removed and reinstalled in this alternative.
4. Structural Cost Implications (Qualitative)
The following table summarizes the qualitative structural cost implications for the two
alternatives under consideration: an earthen berm with MSE walls and a long bridge
(podium). This high-level assessment provides a framework for understanding how each
alternative may impact both upfront investment and lifecycle performance. The qualitative
structural cost implications are listed below.
Table 1 – Qualitative cost implications
Aspect Earthen berm Long bridge
(podium)
Initial structural cost Lower Higher
Foundation cost Lower Higher
Future Utility relocation risk Higher Lower
Long-term maintenance Lower Higher
Seismic retrofit flexibility Limited Higher
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Structural Alternatives for
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Grade Separation
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