state route 1 lagunitas creek bridge project route 1 lagunitas creek bridge project alternatives...

State Route 1 Lagunitas Creek Bridge Project

Alternatives Analysis Report

California Department of Transportation District 04, Marin County, Route 1

PM 28.4 – 28.6 0400001986 EA0G6420

April 2017

Statement of Compliance: Produced in compliance with National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) requirements, as appropriate, to meet the level of analysis and documentation that has been determined necessary for this project.

For individuals with sensory disabilities, this document can be made available in Braille, large print, on audiocassette, or computer disk. To obtain a copy in one of these alternate formats, please call or write to Caltrans, Attn: Eric DeNardo, 111 Grand Avenue, Office of Environmental Analysis, Oakland, CA 94623-0660; (510) 286-5645, Voice, or use the California Relay Service TTY number, 711.

State Route 1 Lagunitas Creek Bridge Project Alternatives Analysis Report v

Table of Contents

List of Abbreviated Terms ...................................................................................................... vii Chapter 1 Introduction ................................................................................................... 1

1.1 Project Setting .................................................................................................. 1 1.2 Bridge History ................................................................................................. 3 1.3 Future Conditions ............................................................................................ 4

Chapter 2 Purpose and Need .......................................................................................... 7 2.1 Purpose ............................................................................................................ 7 2.2 Need ................................................................................................................. 7

2.2.1 Live Load ................................................................................................... 7 2.2.2 Seismic Strength ........................................................................................ 7 2.2.3 Road Safety ................................................................................................ 9

Chapter 3 Alternatives Analysis Process ..................................................................... 11 3.1 Scoping Process and Public Input .................................................................. 12 3.2 Establishment of a Stakeholder Working Group ........................................... 14

Chapter 4 Full Range of Alternatives .......................................................................... 17 4.1 Early Screening .............................................................................................. 17

4.1.1 Transportation System Management and Transportation Demand Management ............................................................................................. 17

4.1.2 New Bridge on New Alignment .............................................................. 17 4.2 No-Build Alternative ..................................................................................... 18 4.3 Replacement Bridge Alternatives .................................................................. 18

4.3.1 Bridge Types ............................................................................................ 18 4.3.2 Construction Methods .............................................................................. 20

4.4 Retrofit Alternative ........................................................................................ 21 4.5 Full Range of Alternatives ............................................................................. 21

Chapter 5 Narrowing the Alternatives ......................................................................... 23 5.1 Screening Criteria .......................................................................................... 23 5.2 Meeting Purpose and Need ............................................................................ 24 5.3 Practicality and Feasibility of Alternatives .................................................... 24

5.3.1 Retrofit Alternative .................................................................................. 24 5.3.2 Conventional Construction Methods ....................................................... 24

5.4 Minimize Community and Environmental Impacts ....................................... 25 5.4.1 Property Impacts ...................................................................................... 25 5.4.2 Duration and Intensity of Impacts ............................................................ 26 5.4.3 Sensitive Habitat Impacts ........................................................................ 26 5.4.4 Hydraulic Impacts .................................................................................... 27

5.5 Fiscal Responsibility ...................................................................................... 28 5.6 Summary of Alternatives Considered but Dismissed .................................... 29

Chapter 6 Project Refinements .................................................................................... 33 Chapter 7 Range of Alternatives Moving Forward ...................................................... 37

List of Tables

Table 1 Elements of the Project Alternatives that have Physical Effects on the Environment ................................................................................................ 27

Table of Contents

State Route 1 Lagunitas Creek Bridge Project Alternatives Analysis Report vi

List of Figures

Figure 1 Project Vicinity .............................................................................................. 2 Figure 2 Photograph of the Lagunitas Creek Bridge, 1906 .......................................... 4 Figure 3 Diagonal Cracks in the Abutments ................................................................ 8 Figure 4 Four Alternative Bridge Designs ................................................................. 19 Figure 5 Sidewalk within Trusses vs. Cantilevered Sidewalk ................................... 34 Figure 6 Conceptual Cross-sections of Steel Truss Bridge and Concrete Bridge

Types ........................................................................................................... 35 Figure 7 Comparison of Bridge Design Options ........................................................ 36

List of Appendices

Appendix A Seismic Evaluation of Lagunitas Creek Bridge Appendix B Project Alternative Study Plans Appendix C Potential Conceptual Solutions for Bridge Closure

State Route 1 Lagunitas Creek Bridge Project Alternatives Analysis Report vii

List of Abbreviated Terms

ABC accelerated bridge construction

ADA Americans with Disabilities Act

Caltrans California Department of Transportation

CEQA

mph

California Environmental Quality Act

miles per hour

NEPA National Environmental Policy Act

PM post mile

SHOPP State Highway Operation and Protection Program

SR 1 State Route 1

SWG Stakeholder Working Group

TDM Transportation Demand Management

TSM Transportation System Management

State Route 1 Lagunitas Creek Bridge Project Alternatives Analysis Report 1

Chapter 1 Introduction The California Department of Transportation (Caltrans) proposes a seismic upgrade to the Lagunitas Creek Bridge on State Route 1 (SR 1) near Point Reyes Station in Marin County. Based on several years of maintenance, structural assessment surveys, and the current seismic design requirements, Caltrans has determined that the bridge structure must be upgraded.

The alternatives development process is a combination of design, environmental, and community input. The objective is to determine the range of alternatives that meet the project purpose and need, are practical and feasible, minimize social, economic and environmental impacts. This report was prepared in response to the Stakeholder Working Group’s (SWG’s) request for a screening of the full range of alternatives.

Per 40 Code of Federal Regulations 1502.14, “the identification, consideration, and analysis of alternatives are key to the National Environmental Policy Act (NEPA) process and goal of objective decision-making. Consideration of alternatives leads to a solution that satisfies the transportation need and protects environmental and community resources.”

This report documents the alternatives analysis conducted to identify the range of alternatives to be carried forward into the environmental document. The alternatives development, refinement and analyses will continue throughout the environmental process, leading to selection of the preferred alternative.

Caltrans is the lead agency under the NEPA and California Environmental Quality Act (CEQA).

1.1 Project Setting

The bridge is located at SR 1 post mile (PM) 28.5, south of the unincorporated town of Point Reyes Station, and just north of the “T” intersection of SR 1 with Sir Francis Drake Boulevard. Sir Francis Drake Boulevard extends west from SR 1 toward Point Reyes National Seashore and north toward the unincorporated town of Inverness (Figure 1). The existing bridge is approximately 0.4 mile to the east of the San Andreas Fault line. Notable nearby recreation areas include Whitehouse Pool Park adjacent to the project to the west; Point Reyes National Seashore to the south and west; two tracts of the Golden Gate National Recreational Area to the west and north,

FIGURE 1Project VicinityState Route 1 Lagunitas Creek Bridge ProjectEA 0G642, MRN-1 Post Mile 28.4 – 28.6ID: 04-13000350Marin County, California

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Project Location

LEGENDProject AreaGolden Gate National Recreation AreaPoint Reyes National SeashoreWhitehouse Pool ParkTomales Bay Ecological Reserve

Chapter 1 Introduction


and to the east and south; and Tomales Bay Ecological Reserve to the northwest. The bridge was constructed in 1929 by Marin County, and it serves as a vital connection between Point Reyes Station and the unincorporated town of Olema to the south (Figure 1).

SR 1 within the project area is an eligible, but not officially designated, state scenic highway. This is a bridge seismic restoration project funded by the State Highway Operation and Protection Program (SHOPP) 2016/17: Bridge Seismic Restoration (201.113 Program); it is estimated to cost between $8 million and $12.5 million and scheduled for construction from 2019 through 2022.

Lagunitas Creek is the main stem of the largest watershed in Marin County and is considered important habitat for multiple federal and state special-status species. A short distance northwest of the bridge, Lagunitas Creek empties into Tomales Bay, which is located on the San Andreas Fault. The San Andreas Fault is an active fault that has caused several strong earthquakes in northern California.

The current Lagunitas Creek Bridge serves as the main entry point into Point Reyes Station from the south. It is an important connection for emergency services to and from Point Reyes Station, as well as for accessing other services within the community.

1.2 Bridge History

The current Lagunitas Creek Bridge was originally commissioned by Marin County as the western terminus of the Mano-Point Reyes Station road (later named Sir Francis Drake Boulevard) and scheduled for completion by 1929, but did not open for travel until 1930. It was proceeded by an earlier bridge that spanned the entire creek bank to bank. The photo shown in Figure 2 dates from 1906 when the creek was named Paper Mill Creek.

The current bridge is 32 feet wide and 152 feet long. The existing bridge is made up of three spans. The first and third spans consist of reinforced concrete T-beam structures that span 25 feet from the roadway abutments to pile-supported piers located in the creek channel. The middle 101.6-foot-long span is a steel pony truss that is supported by the two piers in the creek. The abutments sit on spread footings, and the bents are founded on piles of unknown depth and strength.


State Route 1 Lagunitas Creek Bridge Project 4 Alternatives Analysis Report

Figure 2 Photograph of the Lagunitas Creek Bridge, 1906

Vehicle speeds along SR 1 vary from 55 miles per hour (mph) to 35 mph on the approach of Lagunitas Creek Bridge. The approach speed to the bridge is marked and in review of the prevailing speeds, accident data and roadway conditions, this speed is appropriately signed.

1.3 Future Conditions

There are no plans with the state or the county to expand the capacity of SR 1 or Sir Francis Drake Boulevard. The growth expected for this area has remained under 2 percent for the past 20 years. Caltrans conducted a review of traffic counts over the past 12 years for both weekday and weekend traffic on SR 1 at Lagunitas Creek Bridge. During the economically strong periods, the bridge carries approximately 700 cars per peak hour during a weekday which increases to above 1,300 vehicles at peak-hour during weekends, when tourism is heaviest. High traffic volumes can extend from 12 p.m. to 8 p.m. on weekends, compared to 1 p.m. to 6 p.m. on weekdays. These volumes have fluctuated downward during economic slower periods, but the volumes are not expected to increase above 1 percent a year. The majority of the landscape surrounding the project is held in public ownership, including the Point Reyes National Seashore, Golden Gate National Recreational Area, Tomales Bay



State Park, and others lands owned by the California Department of Fish and Wildlife.

In brief, the future condition would be reflective of current conditions. No anticipated changes to land uses that may require altering the roadway profile or cross section are expected.


Chapter 2 Purpose and Need

2.1 Purpose

The project purpose is to provide a safe, seismically stable crossing of Lagunitas Creek on SR 1 in Marin County.

2.2 Need

The proposed project is needed to meet current safety and seismic design standards. The Lagunitas Creek Bridge does not meet the American Association of State Highway and Transportation Officials and Caltrans safety and seismic design standards, such as live load, seismic strength, and roadway safety. The following sections describe these deficiencies in more detail.

2.2.1 Live Load Caltrans defines live load capacity as the ability of the structure to safely carry truckloads of a given size. The existing bridge was designed to carry trucks much lighter (15-ton trucks) than present-day trucks (i.e., 36-ton trucks). Modern truck loads can add strain and advance the structural weakening of the existing bridge.

2.2.2 Seismic Strength Modern seismic design standards address a structure’s ability to withstand a significant seismic event. Seismic activity can impart great forces into a bridge structure, causing components of the bridge to buckle or rupture, ultimately undermining the stability or support of the bridge. Compared to current seismic standards, the 1929 design used to construct the bridge is obsolete and does not provide the required resiliency in the event of a strong earthquake.

The bridge’s ability to withstand a seismic load depends on the structural strength and ductility1 of all bridge components, including abutments, T-beam spans, steel trusses, piers, and piles. According to the Seismic Evaluation of Lagunitas Creek Bridge (Appendix A), the following deficiencies in the existing bridge would likely cause the bridge to fail due to a strong seismic event:

• The buried, under-reinforced concrete columns supporting the abutments are susceptible to failure under large bending and shear loads. The abutment columns

1 Ductility: a component’s ability to deform under tensile stress (i.e., being pulled or stretched) without breaking.



are estimated to have a demand-over-capacity ratio of 1.6 to withstand seismic activity. A ratio of over 1.0 indicates that columns are in a brittle state; visual inspection of diagonal cracks in the abutments provides evidence of this (see Figure 3).

Figure 3 Diagonal Cracks in the Abutments

• The substructure-to-superstructure2 connections are inadequate for large seismic displacements. The demand-over-capacity ratio of the bridge piers, which are made of unreinforced concrete, ranges from 1.1 to 2.56, indicating that the piers are vulnerable to seismic activity and in a brittle state.

• The steel trusses could significantly displace horizontally and buckle, which could lead to failure of the steel truss span. The bearing anchor bolts connecting the truss superstructure to the substructure have a shear demand-over-capacity ratio of 2.7 (which should only reach a maximum measure of 1.0 to be safe). These bolts will not be able to transfer the seismic forces to the substructure, which could cause the truss to shear off from the piers and abutments during a seismic event.

2 The substructure for this bridge, made up of the abutments (and piers), supports the superstructure, which consists of the two reinforced concrete T-beam spans and the central steel truss span.



• Piles are of unknown depth and type, and may not have sufficient lateral and vertical support for the substructure. The connection of the pile to the pile cap cold crack or separate, particularly in the liquefiable soils that are present.

• Bridge maintenance records indicate the existing concrete roadway deck is worn and weathered and in need of replacement.

• The critical steel truss components and floor beams have large amounts of built-up rust on their surfaces. Reinforcing the truss may require replacing each member of the truss with new steel, which would add weight to the structure.

In addition, the steel truss span has no redundant structural elements; therefore, if any key structural connection or component is compromised, the bridge could fail during a seismic event or under heavy live loads.

2.2.3 Road Safety Safety standards for roadway design consider speed, transportation modes, and surrounding land use. Roadway safety standards consider the size of current vehicles using the road and the required safe distances between motorized and non-motorized traffic. The existing bridge has 11-foot-wide lanes, 2-foot-wide shoulders, and a 3-foot-wide sidewalk (which is not up to safety design standards). The Americans with Disabilities Act (ADA) requires 6-foot-wide sidewalks in constrained areas such as bridges. Further, the existing bridge and the shoulders along SR 1 fail to provide continuous access for multimodal forms of transportation such as bicyclists, equestrians, and pedestrians in the project area.

In accordance with Caltrans ADA guidance in Section 4.2 of the Design Information Bulletin 82-05, Caltrans discussed the non-motorized accessibility with community members and with the Safety Routes to School program leader in Marin County. The resulting input includes concerns about the lack of a safe crossing at Sir Francis Drake Boulevard and SR 1.

In addition, Caltrans received input that the shoulder north of the bridge creates unsafe conditions for pedestrians and bicyclists. Currently, non-motorized travelers proceeding north to Point Reyes Station cross to the west side of SR 1, south of the bridge, then cross the bridge using the walkway located on the west side, and continue on the west side of SR 1 into Point Reyes Station (Caltrans 2017).3 The west

3 California Department of Transportation (Caltrans). 2017. Natural Environment Study Lagunitas Creek Bridge Replacement Project. January.



shoulder is bound by the roadway to the east and to the west. On the west side, the Whitehouse Pool Park, the terrain drops approximately 2 to 5 feet without a protective barrier in place. Also, an overflow culvert under the roadway, located north of the bridge, narrows the shoulder to less than 1 foot wide, which requires pedestrians or bicyclists to use the vehicle travel lane. This narrow area of the shoulder immediately follows a curve in the road, which may cause southbound vehicles to veer into the narrow shoulder.

This document provides a record of the process of gathering input on project development and how public and stakeholders input has shaped and help to narrow the range of reasonable alternatives to be carried into further environmental review process consistent with NEPA and CEQA.


Chapter 3 Alternatives Analysis Process The Federal Highway Administration’s (FHWA’s) NEPA and Transportation Decision-making guidance states, “Alternatives analysis should clearly indicate why and how the particular range of project alternatives was developed, including what kind of public and agency input was used. In addition, alternatives analysis should explain why and how alternatives were eliminated from consideration. It must be made clear what criteria were used to eliminate alternatives, at what point in the process the alternatives were removed, who was involved in establishing the criteria for assessing alternatives, and the measures for assessing the alternatives’ effectiveness” (FHWA 2016).4

Typically, the first step in the NEPA and CEQA process is to conduct scoping, which solicits input from the public and agencies on the scope of the project, range of alternatives and potential resources or issues that may be affected by the project. Following a full scoping process, the project team incorporates the input into the development of a reasonable range of alternatives. Often there are several alternatives that could meet the project purpose, but not all alternatives are carried through the entire environmental review process. Screening based on degree of impact, practicality and feasibility helps to focus the detailed environmental analysis on viable alternatives.

Once the alternatives are narrowed down, the draft environmental analysis is prepared and published for the public and agencies to review, comment, and provide additional input. This input is another step in narrowing the alternatives. The project proponent incorporates this feedback, as necessary, updates the environmental analysis to respond to the comments, then publishes the final environmental document. Only after the publication and review of the final environmental document does the project proponent make a decision on the project.

This alternatives analysis discussed herein precedes the environmental review process. The objective is to determine the range of alternatives to be carried through the detailed environmental review. This Alternatives Analysis Report provides the record of how Caltrans implemented NEPA and CEQA process steps, integrated public and agency input as well as the expertise of an interdisciplinary team to review a reasonable range of alternatives and narrow to those that meet the project purpose 4 Federal Highway Administration (FHWA). 2016. NEPA and Transportation Decisionmaking. Online: https://www.environment.fhwa.dot.gov/projdev/tdmalts.asp. Accessed May 11, 2016.

https://www.environment.fhwa.dot.gov/projdev/tdmalts.asp

Chapter 3 Alternatives Analysis Process


and needs while also avoiding and minimizing social, environmental and economic impacts. The Lagunitas Creek Bridge project alternatives analysis process included the following steps:

1. Gathering input on preliminary range of bridge types and construction through the environmental scoping with a public meeting and an extended 60-day comment period

2. Holding a follow-up public meeting to communicate updates to the alternatives and construction methods and receiving public input

3. Engaging the SWG to receive more detailed community input

4. Narrowing and refining project alternatives

5. Writing this report documenting each step above and providing justification for narrowing alternatives.

3.1 Scoping Process and Public Input

The Lagunitas Creek Bridge Project scoping process began with a Notice of Preparation with the California State Clearinghouse and notices place in the Marin Independent Journal on March 12, 2015. These announcements started the 30-day scoping process which was later elongated to 60 days upon public request. A public scoping meeting was held on March 19, 2015, at the West Marin Elementary School in Point Reyes from 7:00 p.m. to 9:00 p.m. The scoping meeting was organized in an open house format, where various informational stations staffed by Caltrans representatives showed several bridge type options, including a retrofit option; additionally, informational stations displayed environmental issues, construction phases, and other potential impacts to the proposed project.

Caltrans received a total of 63 comment submittals during the scoping period. Comments came from regulatory agencies, private organizations, non-profit groups, and members of the public. Comment themes from the scoping comments included the following:

• Provide more information on the structural vulnerabilities and investigate retrofitting the existing bridge.

• Maintain the current character (e.g., color) and scale of the bridge.



• Keep the construction period short to minimize impacts on traffic and effects on tourism and the business community.

• Minimize construction and the bridge design effects on the sensitive wetland and riparian habitats surrounding Lagunitas Creek and the species they support.

• Minimize impacts on adjacent property owners.

• Conduct a safety analysis of the intersection of SR 1 with Sir Francis Drake Boulevard and Sir Francis Drake Boulevard with Bear Valley Road.

• Plan for the changes associated with sea level rise over time.

After reviewing comments and issues, Caltrans held a second public meeting to respond to some concerns through further information on design and construction. Caltrans followed up with an Informational Meeting on October 14, 2015, to address some of the issues that were raised during the scoping period. In addition to an open house format with presentation boards, the informational meeting included a presentation that provided an overview of the project; a summary of issues heard during the scoping process; updates on information gathered (such as information on sea level rise); and a review of build alternatives, retrofit feasibility, and the accelerated bridge construction (ABC) methods under consideration. A considerable period of the meeting was dedicated to the ABC method, as this addressed the public’s most vocal concern – the fear that a 3-year construction period would result in difficult economic impacts to the rural community that are dependent on tourism and frequent commerce deliveries via SR 1 and the Lagunitas Creek Bridge in and out of the Point Reyes Station and vicinity. The ABC method is an expedited construction method requiring less than 1 year, with the trade-off that there would be a complete closure of the bridge crossing for a 2- to 3-week period.

Caltrans received positive feedback from the public, but it was made apparent that the community wanted to remain involved in the project development process.

Since public forums do not allow for efficient communication and collaboration, Caltrans established an SWG where project details could be conveyed and input could be meaningfully incorporated. The objective of NEPA is to consider a reasonable range of alternatives to help inform the decision-makers. The first step of alternatives analysis is to avoid and minimize foreseeable impacts. The SWG’s role was to act as community liaisons to provide Caltrans with constructive input on the range of



alternatives to be reviewed in the environmental analysis process. The SWG helped to inform how the bridge and construction methods could impact the community so that Caltrans could refine the alternatives prior to environmental review.

The SWG reviewed engineering details of the bridge alternatives, provided Caltrans with input, and asked for additional information needed to understand the trade-offs between different bridge designs and construction methods. This process does not replace public input prior to decision. The public will be asked to review the range of alternatives and the environmental analyses which will provide comparative review of the range of alternatives.

While the alternatives analysis did include the SWG’s input, the SWG does not have decision-making power. The remainder of this report outlines how the public and SWG participated to provide input on the range of alternatives to be carried forward for further environmental review.

3.2 Establishment of a Stakeholder Working Group

To continue to incorporate community input in developing and refining the range of alternatives, Caltrans worked with Marin County Supervisor Kinsey’s office to identify representatives to form an SWG to provide Caltrans with community input. Caltrans requested that the representatives be known and trusted spokespersons for existing community groups that represent the range of community interests, including businesses and tourism, farming and property ownership, safety and public services, community aesthetics, and environmental interests. The nature of the project only required a brief number of meetings to learn about the engineering and environmental constraints, range of aesthetic options and provide input on comparative data for each of the alternatives. Therefore, the representatives were only committing to 3 or 4 meetings of up to 2 hours each, spanned over 4 months.

Supervisor Kinsey’s office sought participation and provided Caltrans with most of the following willing representatives and through interviews; the following additional representatives were identified to complete a full range of interests:

• Coastal Commission, Shannon Fiala

• Pt. Reyes Village Association, Chuck Eckart

• Business Community, Amanda Eischstaedt



• Marin Department of Public Works, Dan Dawson

• Marin County Planning and Parks, Curtis Havel

• Mainstreet Moms, Cathleen Dorinson

• Emergency Services, Randy Engler

• Farming Community, Lynn Stray

• National Parks Service/National Seashore, Brannon Ketcham

Caltrans conducted preliminary interviews with each individual to make sure each could make the commitment and understood the roles and expectations of engagement. Each member represented an interest or a resource entity that may be directly affected by the project. Members that represented community interests, such as Pt. Reyes Village Association, Business Community, Mainstreet Moms, and Farming Community, were liaisons between the community and Caltrans. SWG meetings were closed to the public; however, meeting summaries are posted online on Caltrans’ Lagunitas Creek Bridge Project website (http://www.dot.ca.gov/dist4/lagunitascreekbridge/).

Three SWG meetings were held from January through April 2016. The informal roundtable forum allowed the 12-member SWG to review project details with project staff, ask questions, and understand elements of flexibility in the design. Caltrans provided project details to help the members understand and compare the alternatives, explore the trade-offs between the two construction methods, understand environmental considerations (both construction and operational impacts), potential mitigation measures, and costs associated with each alternative.

To facilitate the SWG members in acting as liaisons with the broader community, similar information as that discussed in the SWG meetings was condensed into two newsletters (March 2016 and June 2016) that were distributed to the public via postal service and web postings. The newsletters provided technical context to help facilitate SWG’s discussions with the public to gather qualitative information to bring into the SWG meeting discussions and help prepare the public to better understand the trade-offs between the alternatives.

http://www.dot.ca.gov/dist4/lagunitascreekbridge/


Chapter 4 Full Range of Alternatives This chapter provides an overview of all the project alternatives including those that were considered prior to narrowing down to those Alternatives that were carried forward for a full environmental analysis. The full range of alternatives considered includes a No-Build Alternative, several replacement bridge alternatives, a retrofit alternative, and alternatives that were screened out early in the planning process, such as a new alignment involving relocating SR 1 and the Lagunitas Creek Bridge and Transportation System Management (TSM) and Transportation Demand Management (TDM) Alternatives.

4.1 Early Screening

TSM and TDM strategies and considering a new alignment for a bridge replacement were screened early in the process and not carried forward into the screening process. The following describes the reasons for not carrying these alternatives forward.

4.1.1 Transportation System Management and Transportation Demand Management TSM and TDM are strategies that can be used to manage traffic flow and congestion. Example strategies of TSM include adjusting signal timing or vehicle detection systems to change signals. Examples of TDM are to influence the volume of traffic by providing incentives to carpool or to adjust the timing of commuter travel to reduce the numbers of vehicles during high peak period commute hours. The project need does not include managing traffic flow and volume; therefore TSM and TDM were not considered for the Lagunitas Creek Bridge Project.

4.1.2 New Bridge on New Alignment A new alignment for the bridge and roadway would require relocating several residents and businesses and disturbing open spaces and/or parks facilities, and would result in environmental impacts substantially greater than the Build Alternatives under consideration. To avoid relocating many homes and businesses, SR 1 would have to be realigned to avoid Point Reyes Station. The shortest distance to avoid the town and re-connect with the northern portion of SR 1 would impact Golden Gate National Recreation Area, which lies to the east of SR 1 south of Point Reyes Station. This realigned roadway would bisect large open space and grazing areas. Section 4(f) of the Department of Transportation Act of 1966, which is codified in federal law in Title 49 of the United States Code in Section 303 (Section 4(f)), requires federal

Chapter 4 Full Range of Alternatives


projects to avoid the use of park lands unless there is no prudent or feasible alternative. This new crossing of Lagunitas Creek would be located east of Point Reyes Station where there are no developed areas. Environmental impacts would involve farmlands, sensitive riparian habitats, and wetland habitats. It could also mean that fewer visitors would drive through Point Reyes Station, which would negatively affect the economy of the community. A new alignment would not provide enhancements to the roadway and crossing beyond those offered by the current location. Therefore, a new alignment was not carried forward as a project alternative.

4.2 No-Build Alternative

The No-Build Alternative, under which the existing Lagunitas Creek Bridge would not be replaced or retrofitted, would consist only of the continuation of ongoing routine maintenance and no other changes. This is the first alternative under consideration and labeled as Alternative 1: No-Build Alternative.

4.3 Replacement Bridge Alternatives

4.3.1 Bridge Types The alternatives development process is a combination of design, environmental, and community input. Caltrans engineers developed a full range of potential bridge type designs which were presented at the public scoping meeting held in Point Reyes Station in March 2015. Feedback during this meeting resulted in including a retrofit alternative and expanding construction approaches to include an expedited method. The full range of alternatives consisted of a combination of four bridge types (three-span short steel truss bridge, three-span concrete bridge, full-span steel truss bridge, and suspension bridge; see Figure 4) and two different construction approaches: conventional construction and ABC. In addition, new alignments and TSM/TDM were considered, but were eliminated early as discussed above.



Three-Span Short Steel Truss Bridge

Three-Span Concrete Bridge

Figure 4 Four Alternative Bridge Designs

Full-Span Steel Truss Bridge

Suspension Bridge



4.3.2 Construction Methods The two construction approaches are described briefly below:

• Conventional construction would last nearly 3 years. A temporary detour bridge would be built immediately to the east of the existing bridge in the first year to detour traffic over the creek, followed by removing the existing bridge the following year, and then the third year, would involve building a new bridge and removing the detour bridge. The construction sequence is long because the construction period is constrained by restricted short allowable periods for in-water work (June to October) in order to minimize impacts on protected wildlife species, and because construction of a detour bridge would be required.

• Accelerated Bridge Construction (ABC) can reduce the construction duration to less than one year and maintain traffic on the existing bridge except for approximately 2 to 3 weeks (during which the bridge would be closed) while the existing bridge is removed and the new bridge is moved into position. During the closure, the shortest available detour is 9 miles long, requiring approximately 18 minutes of additional travel. The ABC shorter construction period is possible by pre-casting and pre-assembling the majority of the bridge components and installing foundation components outside the existing bridge while traffic is maintained on the existing bridge. This method also avoids the time and effort of building a temporary bridge to redirect the traffic away from the construction zone. This approach is not possible for the retrofit or the suspension bridge, and depending on the bridge type, would vary slightly.

The replacement bridge alternatives were combined as follows:

• 2a. Three-span, short steel truss, ABC, longitudinal move-in

• 2b. Three-span, short steel truss, conventional (includes building a detour bridge)

• 3a. Three-span, concrete bridge, ABC, longitudinal move-in

• 3b. Three-span, concrete bridge, conventional (includes building a detour bridge)

• 4a. Full-span, steel truss, ABC, longitudinal move-in

• 4b. Full-span, steel truss, ABC, transverse slide-in

• 4c. Full-span, steel truss, conventional (includes building a detour bridge)

• 5. Full-span suspension bridge, conventional (includes building a detour bridge)



4.4 Retrofit Alternative

The SWG and Caltrans explored the possibility of retrofitting the existing bridge as an alternative to bridge replacement. Caltrans engineers outlined what would be required as follows:

• A 3-year-long construction period

• Rebuilding or removing and refurbishing many elements of the bridge (including piers, pilings, steel members, concrete deck, railing, etc.)

• Building a temporary detour bridge in order to maintain circulation during construction

• Extensive work in the creek to build a support structures would require diverting the creek waters

However, there would be no improvements to sidewalks for bicycle or equestrian users. The current sidewalk conditions do not meet the ADA width requirements, and under the retrofit alternative this lack of compliance would continue due to the constraints of the existing bridge dimensions. The look and scale would be similar to the existing bridge, but the Retrofit Alternative would result in several elements being enlarged to meet seismic requirements. For example, the steel members would be thicker and the piers and abutment foundations would be enlarged, while the lanes would be narrowed to install protective railings needed for safety purposes.

4.5 Full Range of Alternatives

Combining the bridge types with the compatible construction methods options for that bridge type results in the following 10 alternatives that were considered:

1. No-Build

2a. Three-span, short steel truss, ABC, longitudinal move-in

2b. Three-span, short steel truss, conventional (includes building a detour bridge)

3a. Three-span, concrete bridge, ABC, longitudinal move-in

3b. Three-span, concrete bridge, conventional (includes building a detour bridge)

4a. Full-span, steel truss, ABC, longitudinal move-in

4b. Full-span, steel truss, ABC, transverse slide-in



4c. Full-span, steel truss, conventional (includes building a detour bridge)

5. Full-span suspension bridge, conventional (includes building a detour bridge)

6. Retrofit existing bridge, conventional (includes building a detour bridge)

The Project Alternative Study Plans for all bridge alternatives are provided in Appendix B.


Chapter 5 Narrowing the Alternatives

5.1 Screening Criteria

Before the SWG and Caltrans explored the full range of alternatives, they reviewed the process for how alternatives can be narrowed to a reasonable range of alternatives. The Caltrans team explained that all alternatives must meet the purpose and address the needs of the project, and must be determined to be practical and feasible. An alternative is determined to be practical and feasible by whether the alternative design and/or construction method requires, comparatively, an exorbitant use of resources to meet the same outcome of the remaining alternatives given the environmental context. Finally, the SWG provided their criteria for protecting important resources. This generally consisted of minimizing impacts on the community (economy, visual quality, and accessibility) and natural environmental resources (habitat, park and open space). The full list of screening criteria developed for the project alternatives are as follows:

1. Meet project purpose and need to achieve current safety and seismic requirements

2. Alternatives should be practical and feasible

3. Minimize Impacts on the Community as measured by:

• Minimize property acquisition

• Duration of construction disturbance

• Degree of noise, dust and visual blight during construction

4. Minimize Impacts on the Environment as measured by:

• Smallest construction footprint

• Least impact on water resources: water quality, hydraulics, floodplain

• Minimize vegetation removal

The following section reviews how these topics were evaluated in relation to the Alternatives.



5.2 Meeting Purpose and Need

As mentioned earlier, the purpose of the proposed Lagunitas Creek Bridge project is to provide a safe, seismically stable crossing over the Lagunitas Creek on SR 1 in Marin County. While each of the bridge replacement alternatives would meet the purpose and need, the retrofit alternative would not meet the need of improving existing safety deficiencies due to current ADA requirements and current safety guidelines for travel lane width and shoulders. It would meet the purpose to meet seismic standards.

5.3 Practicality and Feasibility of Alternatives

In reviewing this screening criterion for each of the Alternatives, the SWG found the discussion focusing on two subjects: the Retrofit Alternative and the Conventional Construction methods of the replacement alternatives.

5.3.1 Retrofit Alternative A detailed retrofit approach was prepared and made available to the public and the SWG via the project website (http://www.dot.ca.gov/dist4/lagunitascreekbridge/). Through discussion of the substantial deficiencies in the structural integrity of the existing bridge and the uncertainty regarding the extensiveness of the efforts that would be necessary to complete the retrofit, the SWG determined that they were not supportive of the Retrofit Alternative. They reasoned that because the Retrofit Alternative would prove to be an extensive effort, result in comparatively higher environmental impacts than other alternatives under consideration, and not provide improvements for multimodal connectivity (such as pedestrians, bicyclists and equestrian users), this alternative was found to be less than practical.

5.3.2 Conventional Construction Methods In comparative review of the two construction methods, the SWG was unanimous that the conventional construction method requiring 3 years was not acceptable for the community’s economic stability that greatly relies on tourism and movement of goods via SR 1. Additionally, the 3-year construction period would result in elongated impacts on the ecosystem and aesthetic values surrounding the bridge site.

The trade-off with the ABC method is a complete closure of the bridge crossing of up to 3 weeks, and an added risk factor during construction of unforeseen incidents during a high-pressure, around-the-clock construction process potentially resulting in unexpected cost. The mostly likely detour is approximately 9 miles to return to the

http://www.dot.ca.gov/dist4/lagunitascreekbridge/



other side of the creek. This detour can result in hardship for several entities: school routes, emergency services, farm product delivery, and tourists, among other travelers. Together with the SWG, Caltrans reviewed measures to overcome the 3-week closure, which are provided in Appendix C. The SWG requested that Caltrans further explore whether the obstacles and hardships associated with the closure can be resolved. The SWG identified various issues that would have to be overcome in order for a full closure to be feasible. Obstacles to be studied further included access for school and businesses, emergency service response time and access, and safety of the detour route in terms of sufficient maneuvering space for large trucks. So while conventional construction seems to result in much higher use of resources, it provides a practical solution if the 2- to 3-week closure of the ABC method is infeasible.

5.4 Minimize Community and Environmental Impacts

Based on the resources that concerned the SWG, a preliminary review of community and environmental impacts were presented to the SWG for all the alternatives. The majority of the community impacts are associated with use of private property as well as the duration and intensity of the construction period, whereas the natural environmental impacts are closely aligned with the area of disturbance, which is also referred to as the construction limits. To review the different aquatic effects between the bridges, a hydraulics analysis was accelerated to determine whether water flows would vary between the three-span bridges that would have piers in the water versus the full-span steel truss bridge with no piers in the water.

5.4.1 Property Impacts Caltrans worked to minimize the need for property acquisition on all alternatives. However, due to physical constraints, the suspension bridge towers would have to be supported by large foundations, likely requiring property acquisition, which may also entail relocating one combined business/residence. Constructing any of the alternatives would require temporary construction easements on several private properties for staging equipment and accessing the bridge construction site. The properties affected include private homes, a veterinary clinic (for which there is heightened community concern), park land owned by the Department of Conservation, and two empty lots. Any use of land for the purpose of the project is required to adhere to the Uniform Relocation Assistance and Real Property Acquisition Act of 1970, which would provide fair compensation for use of the land and mitigation to restore property following construction. None of the remaining



alternatives would require permanent property acquisition because the bridge and associated improvements would use the existing alignment.

5.4.2 Duration and Intensity of Impacts As discussed earlier, the ABC methods of a shorter construction period would reduce the duration of project impacts but would have higher intensity in the form of longer construction hours and noise, but for a shorter total period than the conventional method. The conventional method would have lower intensity but the construction duration would be 3 years rather than 1 year. Otherwise, construction noise, dust, and visual intrusion are not expected to vary significantly among the alternatives, except for the Suspension Bridge and Retrofit Alternatives. The large foundations for the Suspension Bridge Alternative would require many more piles than the other bridge alternatives, potentially resulting in long durations of noise and vibratory effects. Furthermore, the suspension bridge is not conducive to applying the ABC method that has received considerable community support. Input from the SWG confirmed that in addition to these failings, the scale of this bridge would not be compatible with the character of the community. Similarly, the Retrofit Alternative would result in long duration of construction, and would involve diversion of creek waters which may expand the construction footprint and lead to substantially higher intensity of impacts on the aquatic environment.

5.4.3 Sensitive Habitat Impacts For impacts on the natural environment, each of the bridges and construction methods would likely result in similar impacts on habitat areas. For instance, the staging areas only range from approximately 1.4 to 1.8 acres between alternatives — a difference of 0.4 acre (see Table 1). The majority of the area disturbed would be for the staging areas, whose locations have been identified based on their proximity to the bridge, and with a preference for areas that are not vegetated. However, these temporary impacts would affect riparian habitat, small areas of wetlands, and creek waters. The primary difference in the area affected between alternatives is whether another bridge would be built alongside the existing bridge. For instance, a temporary detour bridge east of the existing bridge would be required for all the alternatives using the conventional construction method (Alternatives 2b, 3b, 4c, 5, and 6). The ABC transverse slide-in alternative would have similar impacts to riparian habitat from construction of the full-span truss to the east of the existing bridge. The difference in permanently shaded area is over the creek; however, this does not substantially differentiate between the alternatives.



As stated above, the Retrofit Alternative would involve diversion of creek waters to build a support structure for the dismantling, reinforcement and reconstruction of the bridge, which may expand the construction footprint and lead to substantially higher intensity of impacts on the aquatic environment.

Table 1 Elements of the Project Alternatives that have Physical Effects on the Environment

Alternatives Piers in the Water Approximate Staging

Area Needed

Alternative 1: No-Build No change – Piers remain in the water. Not applicable

Alternative 2a: Three-span, Short Steel Truss (ABC- Longitudinal Move-in)

Yes, 2 piers near the existing pier location at edge of waterway

1.4 acres

Alternative 2b: Three-span, Short Steel Truss (Conventional Construction)

Yes, 2 piers located just beyond current bridge width at edge of waterway

1.7 acres

Alternative 3a: Three-span, Concrete Bridge (ABC- Longitudinal Move-in)


1.4 acres

Alternative 3b: Three-span, Concrete Bridge (Conventional Construction)


1.7 acres

Alternative 4a: Full-span, Steel Truss (ABC- Longitudinal Move-in)

No piers in the creek channel 1.4 acres

Alternative 4b: Full-span Steel Truss (ABC – Transverse Slide-in)


Alternative 4c: Full-span, Steel Truss (Conventional Construction)


Alternative 5: Full-span, Suspension (Conventional Construction)


Alternative 6: Retrofit (Conventional Construction)


1.7 acres

Note: The staging areas presented in this table were preliminary and comparative in nature. Following the compilation of this table other elements common to all alternatives (such as culvert lengthening) were added to the project which expanded the required staging areas.

5.4.4 Hydraulic Impacts A hydraulics analysis assessed the differences between the three-span bridge (steel or concrete) and the full-span steel truss, and the impacts to the Lagunitas Creek



floodway from having large diameter pier columns versus having no piers at all in the stream compared to existing conditions. The three-span bridge types would have slightly larger pier columns in the water than the existing bridge along with abutments on the river banks, while the full-span bridge would remove all piers from the water and only have abutments on the river banks. The analysis sought to understand the effect of piers versus no piers in raising flood water levels in light of anticipated sea level rise during a 100-year flood event, as well as the projected total scour conditions on the river bottom at the proposed bridge alternatives.

The hydraulic analysis demonstrated that there would be only a small change (less than 6.4 inches) in flood water elevations due to sea level rise during a 100-year flood event regardless of the bridge type. The hydraulic model finds that a typical 100-year flood event would have a water surface elevation of approximately 16 to 20 feet from river bottom at the bridge location, compared to a modeled normal tidal high-water elevation of approximately 9 feet. The model showed that there would be no change in Federal Emergency Management Agency floodplain boundaries if there were piers in the water, even with the minor rise in flood base elevation (under 0.5 inch), and that while there would be a drop in flood water elevations upstream under the no piers scenario of approximately 1-5 inches, this would still not affect the floodplain boundary. Therefore, the hydraulic analysis shows that there is no substantial difference whether there are piers or no piers in the water.

5.5 Fiscal Responsibility

Cost was not an environmental screening criterion, unless the cost exceeds budget availability, especially when alternatives that meet the purpose and need with relatively few impacts are within the allocated budget. Although it was not a determining factor, the SWG was interested in being fiscally responsible with the development of project alternatives.

A comparative cost estimate was prepared to share with the SWG, where it was shown that the concrete bridge (three-span, ABC longitudinal move-in) alternative would be the least costly, the steel truss (three-span ABC, longitudinal move-in) alternative would follow as the second least costly, while the suspension bridge would be the most costly of all alternatives – more than the conventional construction approach and the retrofit alternative. It was noted that the retrofit bridge and conventional construction methods are higher in cost partially due to the fact that a detour bridge would need to be built.



Costs did further validate that the suspension bridge exceeds resource allocation of the other bridge alternatives, but costs, in and of itself, did not justify further screening project alternatives.

5.6 Summary of Alternatives Considered but Dismissed

Through an interdisciplinary process involving planners, engineers, and the SWG, the following Build Alternatives for the existing alignment were considered but dismissed:

• Alternative 3b: Three-span, concrete bridge, conventional (includes building a detour bridge)

• Alternative 4c: Full-span, steel truss bridge, conventional construction (includes building a detour bridge)

• Alternative 5: Full-span, suspension bridge, conventional construction (includes building a detour bridge)

• Alternative 6: Retrofit existing bridge, conventional construction (includes building a detour bridge)

The following sections summarize the reasons these alternatives were not carried forward by Alternative.

ALTERNATIVE 3B: THREE-SPAN, CONCRETE BRIDGE, CONVENTIONAL CONSTRUCTION, AND ALTERNATIVE 4C: FULL-SPAN, STEEL-TRUSS BRIDGE, CONVENTIONAL

CONSTRUCTION The bridge types associated with Alternatives 3b and 4c are represented in Alternatives 3a and 4a, respectively. The only difference is that Alternatives 3b and 4c include the conventional construction method rather than ABC. Only one alternative with conventional construction (Alternative 2b) is carried forward in the environmental analysis, for the reasons discussed below.

The SWG (and subsequent concurrence with the environmental regulatory agencies) strongly opposed the longer construction period of conventional construction. The following issues contributed to their opposition:

• Effects on the economy.



• Lasting noise, air quality, and debris effects on nearby businesses, including effects on animals in recovery at the veterinarian hospital adjacent to the bridge.

• Prolonged disturbance on the sensitive habitats that support threatened and endangered species associated with Lagunitas Creek.

While opposition is noted, Alternative 2b: Three-span, Short Steel Truss Bridge (Conventional Construction) is carried forward for further environmental review as a point of comparison against the alternatives using the ABC construction method and to disclose the full range of potential impacts associated with the project. Impacts associated with conventional construction in Alternative 2b would be similar among the other two bridge types using this method (Alternatives 3b and 4c5), and therefore Alternative 2b: Three-span, Short Steel Truss (Conventional Construction) will represent the impacts associated with all of the conventional alternatives, eliminating the redundancy of conducting a full environmental analysis on all three.

ALTERNATIVE 5: FULL-SPAN, SUSPENSION BRIDGE The suspension bridge towers would have to be supported by large and deep foundations, which would require relocation of one combined business/residence and permanent use of park land in the Whitehouse Pool Park, located on the northwest side of the bridge. The property impacts would not be avoidable by shifting the bridge because the alignment is constrained on both sides. The other bridge replacement alternatives would not result in substantial permanent property impacts. Construction noise, dust, and visual intrusion would not vary among the alternatives, except for the suspension bridge alternative. The large foundations would require many more piles (as much as three times the number of piles) than the other bridge alternatives, resulting in long durations of noise and vibratory effects. Furthermore, the suspension bridge is not conducive to applying the ABC method. It would require a 3-year construction period. In addition to these issues, the large mass and scale of the suspension towers and foundations would not be visually compatible with the character of the community. Therefore, the suspension bridge was not carried forward for a more detailed environmental review.

ALTERNATIVE 6: RETROFIT EXISTING BRIDGE Caltrans explored the possibility of retrofitting the existing bridge as an alternative to bridge replacement. According to the Seismic Evaluation of Lagunitas Creek Bridge (see Appendix A), many elements of the bridge are extremely vulnerable to failure 5 Note that while the Suspension Bridge alternative also includes conventional construction, this alternative is discussed separately and therefore not included here.



during a seismic event. Caltrans structural engineers explored the methods for retrofitting the bridge and learned that retrofitting the bridge would be complicated by the following issues:

• There are existing bridge deficiencies associated with the piles, piers, and abutments, as well as the truss itself. Virtually every major structural element of the bridge would require reinforcement, replacement, or refurbishing. This effort would be unpredictable and would carry a high risk of unforeseen delays.

• An extensive support structure would have to be built under the bridge to support the bridge during the dismantling and restoration process. Working on reinforcements to the piers and abutments would require removing the bridge deck and T-spans. The presence of thick rust in the truss would require removing gusset plates and thickening the steel members to meet current seismic requirements. Without truss members, the bridge deck could not be supported. The existing bridge does not have redundancy in the structure; therefore, as the bridge is dismantled to be retrofitted, the structure would have to rely on a massive temporary support structure built under the existing bridge and within Lagunitas Creek to avoid collapse.

• A support structure would be difficult to construct and remove within the limited allowable in-water work period mandated by the federal Endangered Species Act to protect threatened and endangered species. A creek water diversion would be necessary. Due to the amount of development on three corners of the bridge, a creek diversion would require relocating a business and/ or residence, large impacts on extensive riparian habitat, as well as substantial changes to Whitehouse Pool Park. As remarked previously, Section 4(f) requires that federally funded projects avoid parklands if there are feasible and prudent alternatives to do so. A creek water diversion has the potential for substantial impacts on protected species and their habitat due to destruction of habitat, large amounts of siltation from new water course, and a narrower channel that would change the water velocity. The regulatory agencies would resist permitting a project that would result in substantial environmental impacts to protected aquatic species if other alternatives with less impact are equally feasible.

• A temporary detour bridge would be necessary to safely maintain traffic circulation during construction for the following reasons:



− There is not enough room on the bridge for both construction workers and moving vehicles, creating safety issues for drivers and workers during the retrofit.

− The temporary support structure would have to be strong enough to carry both the weight of the existing bridge and the weight of passing vehicles.

− The retrofit would likely require removing the bridge deck and truss elements, not only to replace or refurbish but also to access and strengthen the piers and abutments.

• The retrofit would require installing a barrier in the shoulder to protect the bridge truss from collisions, a mandatory safety requirement. This would narrow the lanes from 11 feet to 10 feet wide with only a 1-foot shoulder. Narrowing the lanes would not be in compliance with Caltrans safety design standards. There would be no improvements to sidewalks for bicycle or equestrian users. The current sidewalk conditions do not meet the Americans with Disabilities Act width requirements, and under the retrofit alternative this lack of compliance would continue due to the constraints of the existing bridge dimensions. Meeting the ADA standards is a requirement to receive federal funding.

• Finally, the retrofitted bridge would not resemble the existing bridge because the steel members would be thicker, the piers and abutment foundations would be enlarged, and the lanes would be narrower in order to accommodate the required protective railings.

Because the retrofit alternative would be an extensive effort it would be an imprudent use of resources, would result in comparatively much higher environmental impacts (including use of park land and adverse effects on special status species) than other alternatives under consideration, and would not provide improvements for multimodal connectivity (such as pedestrians, bicyclists, and equestrian users), this alternative was not carried forward into further environmental review.


Chapter 6 Project Refinements The project alternatives are continually being refined to avoid and minimize impacts and reflect community context. Context sensitivity refers to how the project responds to and incorporates community and environment context into the design. The SWG spent portions of each meeting providing valuable input on how the alternatives might mirror the community’s scale and character. This section explains the initial input on how the bridges have incorporated this input.

Scale. Scale refers to the overall size of a structure, whether it’s the width or the height or overall bulk. A consistent message from the community that has been echoed in the SWG meetings, is that the bridge should not detract from the community’s rural, small-town character. Caltrans provided the SWG with a range of bridge cross-sections and truss styles for input. The range of options for lane, shoulder, and sidewalk widths is limited by the requirements of Caltrans’ Highway Design Manual and federal regulations such as the ADA. However, these requirements still allow enough flexibility to show a range of bridge configurations that are compatible with the existing and desired roadway dimensions.

Discussions with the SWG have emphasized that children walking or biking to school, equestrians, pedestrians with strollers or wheelchairs, as well as motorized vehicles and delivery trucks all need to be able to safely cross Lagunitas Creek. However, accessibility for all must be balanced against keeping the bridge as narrow as possible.

One element to help maintain the narrow character of the bridge is to place the sidewalk outside the proposed truss structure as a cantilevered sidewalk, or at least physically separated with a railing from the travel way (see Figure 5 for comparison). The width of the travel lanes is proposed to be 11 feet with a 5-foot-wide shoulder and the cantilevered sidewalk is proposed as 6 feet wide to meet ADA requirements. These measurements are narrower than the Caltrans Highway Design Manual recommends, but they meet rural highway safety standards and allow for easy passage for pedestrians.

Chapter 6 Project Refinements


Figure 5 Sidewalk within Trusses vs. Cantilevered Sidewalk A cantilevered sidewalk (bottom image) would help to visually narrow the bridge.

With the proposed dimensions, and accommodation for the steel truss elements and barrier rails, both the three-span and full-span steel truss bridge alternatives (including a cantilevered sidewalk) would range from 47 feet to 50 feet wide (Figure 6).

The concrete bridge with a rail-separated sidewalk would be approximately 45 feet wide. Sidewalks on both sides, as opposed to just one side, would increase either of the bridges’ width by 6 to 8 feet depending on whether truss or rail barriers are part of the dimensions. The bridge alternatives to be studied will only include one separated sidewalk along the west side of the bridge. Other dimensions of the bridge structure (such as the piers, the truss height, and the elevation of the bridge soffit [underside of the bridge deck]) are determined by the seismic safety design requirements and traffic loading.



Figure 6 Conceptual Cross-sections of Steel Truss Bridge and Concrete

Bridge Types Note: the existing bridge piers are shown in dashed outline for scale comparison. Character. The flexibility in character is determined by the selection of the bridge type and the possible design options associated with each bridge type. For instance, the steel truss structures for the three-span or the full-span bridge could be curved versus angular. Because a full-span bridge must span from creek bank to creek bank, the structural support must include overhead lateral truss bracing, whereas a three-span truss design would not. The concrete bridge could remain open without any structure above the barrier rail, or it could incorporate a faux truss that could, for example, mimic the appearance of the existing bridge truss. Possibilities for each bridge type are shown in Figure 7. These details do not change the environmental impacts associated with operation or construction or the bridge, although they affect the visual character. These design options will continue to be reviewed and explored with the community, even past the environmental review process. Several of the SWG members observed that the concrete bridge type, without the faux truss, offers bridge users more visibility with less visual obstruction looking towards the creek and towards the town, and also less visual obstruction for people at the Sir Francis Drake and SR 1 intersection looking towards and past the bridge.



Three-Span Concrete Bridge Three-Span Concrete Bridge with Faux Truss

Full-Span Steel Truss- Angular Full-Span Steel Truss- Curved

Figure 7 Comparison of Bridge Design Options


Chapter 7 Range of Alternatives Moving Forward

Through collaboration with the SWG, Caltrans narrowed the alternatives to be analyzed in the Environmental Impact Report/Environmental Assessment (EIR/EA; Caltrans 2017).6 In addition to the ABC construction methods for each bridge type considered, one alternative includes the conventional, longer construction method. This alternative will provide a point of comparison and serve as a fallback option in case an unforeseen obstacle prevents use of the ABC methods. The alternatives identified for analysis in the EIR/EA are as follows:

• Alternative 1: No-Build Alternative (project would not occur)

• Alternative 2a: Three-span, short steel truss bridge, ABC, longitudinal move-in

• Alternative 2b: Three-span, short steel truss bridge, conventional (with detour bridge)

• Alternative 3a: Three-span, concrete bridge, ABC, longitudinal move-in

• Alternative 4a: Full-span, steel truss bridge, ABC, longitudinal move-in

• Alternative 4b: Full-span, steel truss bridge, ABC, transverse slide-in

The preference is to limit to one sidewalk on the west side of the bridge, preferably cantilevered and separated from the shoulder and travel lanes. The bridge deck would include 5-foot shoulders and 11-foot travel lanes, which would accommodate equestrians on the shoulder and encourage slower travel speeds for automobiles.

6 California Department of Transportation (Caltrans). 2017. Draft Environmental Impact Report/Environmental Assessment and Section 4(f) De Minimis Determination. April.

State Route 1 Lagunitas Creek Bridge Project Alternatives Analysis Report

Appendix A Seismic Evaluation of Lagunitas Creek Bridge

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Seismic Evaluation of Lagunitas Creek Bridge

Introduction:

This report provides the results of seismic evaluation of Lagunitas Creek Bridge, Br. No. 27-0023.

The seismic evaluation was performed to develop the optimum seismic retrofit strategy and associated

cost. The structure was evaluated in accordance with Caltrans standard practice and Memo to Designers

(MTD) 20-4. The resulting retrofit measure upgrades the bridge to the performance level of “no collapse”.

Service Load Rating analysis was performed separately by Structure Maintenance & Investigations

(SM&I) and is documented elsewhere.

This report is limited in scope to address only the seismic vulnerabilities. Other structural deficiencies

associated with Safety (bridge railing), Americans with Disabilities Act (ADA compliance sidewalk,

bridge width etc.), maintenance needs, and any other functional deficiencies are documented elsewhere.

Bridge Description:

This bridge is located on Route 1 in Marin County and was built in 1929. The bridge is comprised of

three spans of 25.0 ft, 101.6 ft and 25.0 ft, respectively, with a total length of 151.6 ft. The main Span 2

consists of two (2) riveted steel pony trusses supporting steel built-up type floor beams. The reinforced

concrete deck is supported non-compositely by the floor beams. The two short end spans, Span 1 and

Span 3, are reinforced concrete T-beam girders monolithic with deck slab.

The reinforced concrete spans and pony trusses are supported on two unreinforced concrete piers at Bent

2 and Bent 3. The truss at each end is connected to the pier through 6.5 inch high rocker bearing while the

concrete span is monolithically connected through dowels embedded in the diaphragm. Each pier is

founded on an unreinforced concrete cap supported on a 13-pile-group deep foundations. Due to lack of

pile records, identifying type, length and capacity, 12-inch-diameter circular timber piles have been

assumed for this study1. As-built plans show an estimated pile depth of 30 ft.

Both abutments at the end of the bridge consist of lightly reinforced concrete abutment cap (acting as

back wall to retain soil), supported on three 2-ft wide square columns. The columns are lightly reinforced

with four 1-inch square corner bars (longitudinal steel ratio of 0.69%) and 3/8-inch shear stirrups at 12

inch spacing. The ends of the shear stirrups have non-seismic, short length hooks and are considered

1 12” timber piling are the standard pile type used in bridge construction during the era of this bridge

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ineffective for confinement of column concrete. The reinforcement in columns are considered inadequate

in seismic regions and may lead to brittle failure in shear and flexural hinging (i.e. no ductility). The

footings for the columns are 5 foot square and have bottom mat reinforcing consisting of four 5/8-inch

rebar both ways. The footings have no top mat of reinforcement.

The bridge falls under Fracture Critical Bridge/Member definition. No redundancy of the truss structural

system exists, where failure of any critical tension truss members of anyone of the two trusses could cause

bridge collapse.

According to the Preliminary Seismic Design Recommendations, the San Andreas Fault with a maximum

magnitude of 7.9 is located less than one mile from the bridge site. The seismic response spectra used for

the seismic evaluation was based on the Preliminary Seismic Design Recommendations report provided

by Office of Geotechnical Design-West dated July 30, 2010, as below.

The Revised Seismic Design Recommendation dated December 7, 2016, indicates based on borings,

layers of loose to compact granular materials below groundwater table. These soil layers extend up to 25

ft below the ground. The geology of the soil layers, along with high seismicity of the site (0.77g peak

ground Acceleration), calculated Cyclic Stress Ratio, and corresponding Cyclic Resistance Ratio, suggest

liquefaction during seismic event. Further, due to presence of liquefiable layers and topography of the

site, potential for lateral spreading (permanent lateral ground displacement along with settlement) exists.

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Design Parameters:

Material properties: (From As-Built Records or based on bridge era)

Fy = 30 ksi for steel truss member

Fy = 33 ksi for reinforcing rebars

Fy = 36ksi, Fu=58ksi for 1-1/4 inch dia rocker bearing anchor bolts

F’c of the concrete = 3000psi

(Abutment concrete is Class A with 6 sack cement; Pier concrete is Class B with 5 sack)

Stress Limits on the unreinforced concrete: AASHTO LRFD and Caltrans Bridge Design

Specifications LFD

Concrete shear stress = 2√𝑓𝑐′

Concrete fracture modulus, 𝑓𝑟 = 6.3√𝑓𝑐′

Timber Pile: Caltrans Bridge Design Specifications LFD/Timber Pile Design Manual

Design Stress bending Fb= 2500 psi – (Douglas Fir)

Design Stress Shear Fv = 230 psi

Loads:

The Dead Load of the truss span at each rocker bearing is 109 kips. The rocker bearings

are connected to the pier cap with 1-1/4-inch anchor bolts as shown in Fig. 2 and details

on Sheets 2 and 4 of As-Built Plans in Appendix A.

The Dead Load of the concrete span at bent 2 in each pier is 41.9 kips. The bent cap is

connected to the pier top through eight 1-inch square staggered dowel bars – shown on

Sheet 5 of As-Built plans in Appendix A.

Dead load at the abutment is 93 kips on 3 columns, resulting in 31 kips each column.

The column reinforcement detail is shown below in Fig.3. The columns are buried 13 ft

in soil. The point of fixity is taken as 8 ft (4 times the column width).

Design peak seismic spectrum acceleration is 1.8 g.

Fig. 2 - Seismic Lateral Forces-Truss Rocker Bearing and Concrete Span Connection

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Fig. 3 - Abutment Column and Footing Detail

As-Built Analysis in Longitudinal Direction

Bearing connection at superstructure to substructure connection:

Truss span rocker bearing:

The anchor bolts on the rocker bearing of the truss are embedded 1 foot into the

unreinforced concrete pier and develop full shear capacity.

The shear friction design capacity of the two (2) 1¼-inch anchor bolts = 74 kips.

The ultimate capacity including friction is 74+0.4*109=119kips.

The seismic shear demand is 109*1.8=197 kips. Demand/Capacity (D/C) = 197/74=2.7

D/C=197/119=1.7 including friction.

D/C ratios indicate that the anchor bolts will be sheared off under seismic loading.

Concrete span connection to the pier:

Assuming the dowels of the concrete span remain embedded in the pier and do not crack

the pier top. The shear capacity of the dowels is 8*33ksi=264 kips. Since the embedment is

only 2’-10” for 1-inch square bar, it is reasonable to assume the dowels will develop only

70% of the yield stress, which will yield to shear capacity of 186 kips. Compared with the

seismic demand shear of 74+42*1.8=151 kips. D/C = 0.8.

D/C ratio indicates connection is adequate. However, the unreinforced concrete pier top could

crack when transferring this shear demand.

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Abutment Columns: Response spectrum analysis was performed per Caltrans Seismic Design Criteria (SDC). The

columns are fixed at top with the abutment cap beam and at bottom at point of fixity in the soil.

Effective stiffness section properties were used.

The design ARS value is 1.8g.

Seismic moment demand is 216 kip-ft with associated shear demand of 56 kips. The

idealized plastic moment of the column is 192 kip-ft. The D/C ratio is 1.13, indicating plastic

hinging of columns.

The shear demand at plastic hinging of column is 56 kips and the shear capacity is 35 kips.

The shear D/C ratio is 1.6 showing brittle shear failure of the abutment columns just before

plastic hinging failure.

D/C ratio of 1.6 and 1.13 for shear and flexure, respectively, indicates brittle failure of the

abutment column. Large diagonal cracks followed by buckling of the column longitudinal rebars

due to lack of confinement and large stirrup spacing could lead to column brittle failure

mechanism, causing concrete end spans to collapse.

These type of reinforcement in columns provide very little confinement to the concrete and hence

exhibit brittle failure in shear and flexural hinging (i.e. no ductility).

Piers (Unreinforced Concrete): The shear transferred to the concrete pier is the lesser of the design ARS times the total dead

load at the pier or the capacity of the anchor bolts plus friction between the bearing plate on

the pony truss span plus shear transferred through the dowels from the concrete span.

The ARS shear transferred to the pier is (109+42) x1.8=272 kips.

The shear transfer to the concrete pier through dowels from concrete span is 186 kips. The shear transfer through ultimate capacity of anchor bolts from pony truss side is 2x1.23x58 = 143 kips. Total shear 186+143=329 kips.

The controlling shear demand is 272 kips and is used for the capacity evaluation of the pier and pile foundation.

Max. Shear D/C =272/310= 0.88 at the 5-foot diameter pier - see Appendix

Max. Moment D/C=2037/796= 2.56 at the bottom of 5-foot diameter pier – see Appendix.

D/C ratios over the pier height range from 1.1 to 2.56.

The D/C ratios for flexure indicates unreinforced pier has insufficient flexural capacity. Large

diagonal cracking along the height will occur and may result in pier brittle failure.

Piles (timber):

The seismic overturning forces at the bottom of the pier was used to evaluate the shear and axial

forces in the piles.

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Piles are expected to be subjected to 200 kips in tension (uplift) and 265 kip compression

due to seismic overturning moment.

Pile axial tension and compression capacities are expected to be low due to liquefiable soil

layers and shallow pile embedment depth.

Shear demand in each pile is 21 kips (total pier shear demand/no of piles = 272/13). The D/C

= 21/24=0.88.

The high cyclic compression and tension forces in piles will cause large width cracking in the pile to

pile cap connection. In the absence of pile cap and pile anchorage reinforcement, the piles will

separate from pile cap and will not resist overturning seismic lateral forces. The compression piles

will undergo large vertical displacements (i.e. plunging).

The piles have sufficient shear strength but the joint shear stresses at the unreinforced pier pile cap

will fail prior to developing shear demand of the piles.

The failure of the pile to pile cap connection and plunging of the compression piles in liquefiable soil

may lead to overturning failure of the piers.

Truss members:

No redundancy of the truss structural system exists due to some tension members falling under

Fracture Critical Member definition. Overstressing of the Fracture Critical Members of the truss

may occur due to large foundation settlement, which may cause failure of the truss bridge.

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As-Built Analysis in Transverse Direction

The bridge has similar seismic response in transverse direction as in longitudinal direction.

Consequently, results and failure mechanism for longitudinal direction will apply in the transverse

direction.

One difference is the 1 ft wide by 5’-6” deep reinforced concrete wall connecting the two piers as shown

in Fig. 4 below. The wall will strengthen the upper portion of the pier but will transfer damage to the

lower portion of the unreinforced concrete pier.

Fig. 4 - Pier Elevation – Reinforced concrete wall between the piers in transverse direction

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Seismic Vulnerabilities:

Based on the seismic vulnerability analysis, the following deficiencies are identified:

The rocker bearing anchor bolts connecting the superstructure and substructure have a shear

D/C ratio of 2.7. The bolts will not be able to transfer seismic forces to the substructure and will

shear off, causing the steel truss superstructure to fall 8.5 inches off the bearing. The drop of

superstructure along with damage to unreinforced pile cap will result in uneven settlement at

the truss support. This will cause overstressing of the fracture critical members of the truss and

steel floor beam system, leading to possible collapse mechanism.

The unreinforced pier flexural D/C ratio ranges from 1.1 to 2.56. This high flexural demand in

the absence of longitudinal flexural and shear reinforcement in the piers would cause large

flexural-shear cracks and could lead to brittle overturning failure.

The pile-to-cap connection will form large cracks and will fail due to absence of pile cap

reinforcement and pile end anchorage reinforcement. The piles will not be able to transfer

seismic demand forces (axial tension and shear) leading to possible collapse.

The abutment column footings and existing piles are founded in liquefiable soil. During

liquefaction, the abutments footings will settle and piles will plunge. Abutment settlement and

pile plunging may lead to foundation failure.

The abutment columns D/C ratio of 1.6 and 1.13 for shear and flexure, respectively. Large

diagonal cracks followed by buckling of the column longitudinal rebars due to lack of

confinement and large stirrup spacing, could lead to column failure mechanism. Any brittle

failure of abutment columns will cause concrete end spans to collapse.

The connection details, unreinforced pier and pile caps, poorly confined abutment columns and

footings, short timber pile types and pile connections are poor when compared to the design and

detail practice recommended under current AASHTO/Caltrans Seismic Design codes.

The seismic retrofit of the bridge shown in attached “Retrofit Alternative – 1” is needed based on the

above mentioned seismic vulnerabilities.

Recommended Seismic Retrofit:

Seismic upgrade of the bridge will require the following work:

Replace existing bearings at bent 2 and bent 3 with new bearings.

Construct 2 Cast-In-Steel Shell (CISS) piles at each bent.

Construct bent cap at bent 2 and bent 3.

Replace existing non-ductile columns at abutments with seat type abutment.

Retrofit Construction Consideration:

The CISS piles can be constructed with one lane closure.

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9

Construction of bent cap and abutment will require access in the creek under the bridge for

falsework.

Jacking and temporary support will be needed for the existing trusses and concrete span to

replace the existing pier rocker bearings and abutment bearings.

Tariq Masroor

Senior Bridge Engineer/Seismic Specialist

Design Branch 4, Office West

Division of Engineering Services

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Retrofit Alternative - 1

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Appendix:

Design Calculations: D. Lee

Job: Lagunitas Creek Bridge

Item: Longitudinal seismic response in Substructure Pier @ Bent 2, per pier; (Bent 3 similar)

Assumption:

The concrete approach span dowels will maintain fully functional.

The truss seat anchor bolts will maintain fully functional.

f'c ( psi) = 3000

The unreinforced concrete tensile stress capacity = the fracture modulus of concrete = 6*SQRT(f'c) = 328.6 psi

The shear stress capacity of concrete = 2*SQRT(f'c) = 109.5 psi

Vertical force from concrete span (kips) = 109

Vertical force from truss span (kips) = 41.9

Spectra acceleration (g) = 1.8

Unreinforced Concrete Pier Force Demand vs. Capacity

Distance

below the

top of the

pier (ft.)

Cross

secton

Area (sq.

ft.)

I (ft^4)

c (ft.)

Axial

Force

(kips)

Moment

Demand

(k-ft)

Moment

Capacity

(k-ft)

Moment

D/C

Shear

Demand

(kips)

Shear

Capacity

(kips)

Shear D/C

2.00 32.11 85.927 2.83 160.5 543.2 1586.8 0.34 271.6 506.5 0.54

2.10 19.63 31.610 2.50 153.7 570.4 697.4 0.82 271.6 309.7 0.88

4.75 19.63 31.610 2.50 228.9 1290.2 745.8 1.73 271.6 309.7 0.88

7.50 19.63 31.610 2.50 306.9 2037.2 796.0 2.56 271.6 309.7 0.88

7.60 32.49 87.967 2.85 179.1 2064.3 1630.8 1.27 271.6 512.5 0.53

11.00 46.69 181.698 3.42 180.6 2987.8 2722.3 1.10 271.6 736.6 0.37

16.50 75.11 470.140 4.33 203.4 4481.7 5428.1 0.83 271.6 1184.8 0.23

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Checker Calculations: Keith Nakaoka

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As-Built Plans of the Lagunitas Bridge – Sheet 1 to 8

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Appendix B Project Alternative Study Plans

STRUCTURE

DESIGN

BRANCH

AS NOTED

UNIT:

PLANNING STUDY

SCALE:

BRIDGE No.

DATE

DATE

DATE

DATEAPPROVED

CHECKED BY

DRAWN BY

DESIGNED BY

CONTRACT No.: 04-0G640K

POST MILEROUTECOUNTYDIST

0413000350

XX

STRUCTURES DESIGN ADVANCE PLANNING STUDY SHEET (ENGLISH) (REV. 08-09-10)

TI

ME

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=>

09:32

15-J

AN-2016

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04-0g640k-27-0023-lagunitas-aps-alt-1b.dgnFILE =>

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OF

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AN

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N -

DIVISIO

N

OF

ST

RU

CT

UR

ES

PROJECT No. & PHASE:0 1 2 3ORIGINAL SCALE IN INCHES

� Existing

ELEVATION

PLAN

1

Notes

Temporary Railing Type K

Indicates existing structure

Indicates new structure

1" = 40’

1" = 40’

Exist EBExist BB

A B A

To Stinson Beach

To Jenner

2direction controlled by signals

Single lane of alternating traffic

A Existing Reinforced Concrete T-Beam end span

B Existing Steel Truss bridge

Creek

Lagunitas

Approx. OG

3 Concrete Barrier Type 26

25’-0"– 100’-0"– 25’-0"–

151’-7�"–

170’-0"

1

NEW PILES

STAGE 1

PROPOSED

Abut 1

Pier 2 Pier 3

Abut 4

34’-6"

2

3

PILESSTAGE 2PROPOSED

PILESSTAGE 1PROPOSED

3

46’-0"

CONSTRUCTION SEQUENCE

NEW BB NEW EB

PILESSTAGE 2

PILESSTAGE 1

PILESSTAGE 2

PILESSTAGE 1

7’-0" 7’-0"32’-0"

Accelerated Bridge Construction (ABC)ALTERNATIVE 1B

04 Mrn 1 28.51

Peter Soin

Minh Ha

LAGUNITAS CREEK BRIDGE REPLACE

59-3579 27-00234

2

101’-0"

NEW PILES

STAGE 2

PROPOSED

Abut 1Exist

Pier 2Exist

Pier 3Exist Abut 4

Exist

Approx. OG

� Span

Precast P/S SlabPrecast P/S Slab

1" = 20’

STAGE 6:

STAGE 5:

STAGE 4:

STAGE 3:

STAGE 2:

STAGE 1:

Steel Truss

34’-6"

170’-0" (PROPOSED)

151’-7"– (EXISTING)

Jeff Thorne 1-16

1-16

1-16

52’-0"

STEEL TRUSS, 3 - SPAN / (ABC) LONGITUDINAL MOVE - IN

(STEEL TRUSS - MAIN SPAN) TYPICAL SECTION

STEEL TRUSS

Place new Deck and Concrete Barrier Type 26

Place new Steel Truss and Precast P/S Slabs

Place Pier Cap

Remove Existing Bridge

Install second half new Piles & Abutment Cap, K-Rail - 1 Lane open

Install half new Piles & Abutment Cap, K-Rail - 1 Lane open

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STEEL DESIGNED BYP. SoinDRAWN BY A. On ode raCHECKED BY X

APPROVED X

TRUSS, DATE 1 _ 1 6DATE 1 _ 1 6DATE X

DATE X

3-SPAN/ DETOUR BRIDGEf-<( 0

STRUCTURE

DESIGN

BRANCH

4

I')

PLANNING STUDY -

---------------------------1 �

LAGUNIT AS CREEK BRIDGE "'

REPLACE 1-----------------------------lw

UNIT: 59-3579 BRIDGE No. 27-0023 � 1-----------+-----------------1 2

SCALE: AS NOTED PROJECT No. & PHASE: 04 13000350 � -------------------------------------------------------------------------------------------------------------------------------------::::,

STRUCTURES DESIGN ADVANCE PLANNING STUDY SHEET (ENGLISH) (REV. 08-09-10) FILE => 04-0g640k-aps-alt01.dgn CONTRACT No.: 04-0G640K

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Pier 2

Existing Reinforced Concrete T-Beam end span

Existing Steel Truss bridge

Indicates existing structureIndicates new structure

STAGE 2PILES

25'-0"±

0 1·

To Stinson Beach

STAGEPILES

170'-0" (PROPOSED)

151 '-7"±

1 oo'-o"

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[__s- l Span

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DIST COUNTY ROUTE POST MILE

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11 11 11 11 11

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(MAIN SPAN) TYPICAL SECTlON

1" = 20'


1: Instal I half new Piles & Abutment Cap, K-Rail - 1 LaneSTAGE 2: Instal I second ha If new Piles & Abutment Cap, K-Rail -STAGE 3: Remove Existing BridgeSTAGE 4: Place Pier Cap

open1 Lane

STAGE 5: Place new Precast P/S I - Girders and Precast P/S SlabsSTAGE 6: Place new Deck and Concrete Barrier Type 26

open

A II

tt-

'3 Q_

t-

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A II

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<ABC> PRE-CAST ASSEMBLY 1--------------------,..---------------------------------lw

DESIGNED BYPeter Soin

CONCRETE BRIDGE, 3-SPAN

ALTERNATIVE 3A

DATE 1 _ 1 6DRAWN BY M.Lane/ W.Zhang DATE 1- 1 6CHECKED BY X

APPROVED Minh Ha

DATE X

DATE 1 _ 1 6

t-

Accelerated Bridge Construction (ABC) ;::;

STRUCTURE

DESIGN

BRANCH

4

PLANNING STUDY

LAGUNITAS CREEK BRIDGE REPLACE ;;;A II

------------------------tw

UNIT: 59-3579 BRIDGE No.27-0023 �------------------------tiio

SCALE: AS NOTED PROJECT No. & PHASE: 041 3000350 �----------------------------------------------------------------------------------------------------------------------:::,

STRUCTURES DESIGN ADVANCE PLANNING STUDY SHEET (ENGLISH} (REY. 08-09-10) FI LE = > 04-0g640k-27-0023- I a gun i tas-aps-a I t-3b.dgn CONTRACT No.: 04-0G640K

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® Crash cushion

-

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(1) CIP concrete slab (end span)

� New supports at existing support locations



·-----Indicate existing structure

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POST MILE

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()_ -------------------------------------------------------w

CONCRETE DESIGNED BYP. SoinDRAWN BY A. On ode raCHECKED BY X

APPROVED X

BRIDGE, 3-SPAN/ DETOUR BRIDGE f-<( 0

DATE 1 _ 1 6DATE 1 _ 1 6DATE X

DATE X

STRUCTURE

DESIGN

BRANCH

4

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ORIGINAL SCALE IN INCHES O 3

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l Existing

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DIST COUNTY

04 Mrn

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conduits ----------J1--------

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1" = 20'


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1----- ST AGE 1 NEW PILES

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STAGE 2: Instal I second half new piles & Abutment Cap, K-Rai I - 1 lane open "'

STAGE 3: Remove existing bridge.

STAGE 4: Place steel trusses and cross bracings.

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DRAWN BY Jeff Thorne

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4ADATE

1 _ 1 6

DATE 1 _ 1 6

DATE X

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DESIGN

BRANCH

4

PLANNING STUDY

LAGUNITAS CREEK BRIDGE REPLACE ;;; A II

-----------,--------------lw

UNIT: 5 9 -3 5 7 9 BRIDGE No. 27-0023 � -----------------------1iio

SCALE: AS NOTED PROJECT No. & PHASE: 0413000350 � ----------------------------------------------------------------------------------------------------------------:::,

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i Existing c_

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11 '-0" STAGE 1 TRAFFIC

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I I

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DIST COUNTY

04 Mrn

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NEW

32'-o"

ROUTE POST MILE

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TYPICAL SECTION STEEL TRUSS STAGE 1 THRU 3 CONSTRUCTION SEQUENCE

STAGE 3: Construct New Truss Bridge to East.

STAGE 4: Remove Existing Bridge and slide New Truss Bridge West into place. (Long Weekend)

STAGE 5: Remove remaining existing foundations.

REMOVE EXISTING BRIDGE

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To Jenner c::::::>

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PLANNING STUDY

LAGUNITAS CREEK BRIDGE REPLACE ;;; A II

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UNIT: 5 9 -3 5 7 9 BRIDGE No. 27-0023 �-----------------------1iioSCALE: AS NOTED PROJECT No. & PHASE: 0413000350 �

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APPROVED X

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DATE X

STRUCTURE

DESIGN

BRANCH

4

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PLANNING STUDY -

---------------------------1 �


REPLACE 1-----------....-----------------lw

UNIT: 59-3579 BRIDGE No. 27-0023 � 1-----------+-----------------1 2

SCALE: AS NOTED PROJECT No. & PHASE: 0413000350 � -------------------------------------------------------------------------------------------------------------------------------------::::,


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SUSPENSION

DESIGNED BYp. Soi n DATE 1 -1 6DRAWN BY A. Onodera DATE 1 -1 6CHECKED BY X DATE X

APPROVED X DATE X

BRIDGE/ DETOUR BRIDGE f-<( 0

STRUCTURE

DESIGN

BRANCH

4

PLANNING STUDY �

---------------------------1�


REPLACE 1-----------....-----------------lw

UNIT: 59-3579 BRIDGE No. 27-0023 � 1-----------+-----------------1 2

SCALE: AS NOTED PROJECT No. & PHASE: 0413000350 � -------------------------------------------------------------------------------------------------------------------------------------::::,


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ELEVATION ¥l211 = 1 '

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-----------------------------------------------

PIER 3

l<::�:].:._. - - - . - . - - - . - . - - - . - . - - . - . - - - . - . - - - . - . - - - . - . - - - . - . - - - . - . - - - . - . - - - . - . - - - . L

ROADWAY

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r------------------------- -------------------------------------------------,

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2

TEMPORARY STRUCTURE FOR TRAFFIC DETOUR AND PEDESTRIAN WALKWAY

PLAN � II : 1'

RISK AND ASSUPMTION NOTES:

1. Ful I closure of bridge during construction.2. Detour traffic during construction.3. Detour has right of way impact.4. Contruction wi 11 take two seasons.5. Foundation work in creek.6. Temporary falsework in creek.7. Bridge cannot carry permit loads.

8. Side walk may not comply with ADA requirements.9. Detour not shown.1 o. California ST-1 O Bridge Roi I can be modified to

fit between truss post. 11. Additional members that require replacement may

be discovered during construction.


STRUCTURES DESIGN ADVANCE PLANNING STUDY SHEET (ENGLISH} (REY. 08-09-10)

DIST COUNTY ROUTE POST MILE

8"¢ WATER PIPE-

04 M r n 28. 5 1

(t EXISTING ! 50'-0" � (t TEMPORARY STRUCTURE --------..;�1·�---------------i•, STRUCTURE

5'-0"±

I I

56'-o" 38'-o" I

32'-4"± ! 26'-o" 13'-8"± 13'-8"±

EXISTING 4-4 "¢ -i====��::::;:::::::::::.:::::.:.::::.:;;::::::::;:=::;:::=::::;:=tg_, ___ ---l ELECTRICAL CONDUITS r-·-r r-·-r

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TYPICAL SECTION

TEMPORARY STRUCTURE FOR TRAFFIC DETOUR AND PEDESTRIAN WALKWAY

1" = 1 O'

TRAFFIC STAGING

Ful I bridge closure is required for the E>ridge retrofit

Indicates existing Indicates new construction Replace existing bearings with seismic isolation bearings Replace exisitng bridge deck Replace top flanges of al I floor beams Replace al I existing gusset plates Replace existing expansion joints Replace existing guard rai I Replace top and bottom plates of the top chords Replace bottom braces

Replace al I damaged rivets with high strength bolts New P/C concrete slab New California ST-10 Bridge Rail Replace existing abutment

RETROFIT ALTERNATIVE 6

DESIGNED BY DATE STRUCTURE Yon Pi I Kim X PLANNING STUDY DRAWN BY DATE DESIGN

Antonio Carreon 10-09-15 BRANCH LAGUNITAS CREEK BRIDGE RETROFIT

CHECKED BY X DATE X

8APPROVED X DATE XUNIT: 3 59 3

PROJECT No. & PHASE: 0413000350, BRIDGE No. 27-0023

SCALE: X FILE => 04-0g640k_aps_alt1 .dgn CONTRACT No.: 04-0G642

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Appendix C Potential Conceptual Solutions for Bridge Closure

State Route 1 Lagunitas Creek Bridge Project Alternatives Analysis Report C-1

Lagunitas Creek Bridge Project: Potential Conceptual Solutions for Bridge Closure A short-term closure of the Lagunitas Creek Bridge would be necessary if the Accelerated Bridge Construction (ABC) approach is selected for the Lagunitas Creek Bridge Project. The purpose of this memorandum is intended for the Stakeholder Working Group to discuss the range of possible effects and potential solutions for crossing the Lagunitas Creek Bridge on SR 1 at the north bound entrance to Point Reyes Station.

Conventional construction would require three seasons to complete the project: one season for building a temporary bridge, one season for demolition of the existing bridge, and one season for building a new bridge and removing the temporary bridge. This method would preserve two-way access across Lagunitas Creek for a majority of the construction period, except for occasional one-way traffic in late evenings or other low traffic volume periods.

The ABC method would primarily involve working around the bridge for foundation support and offsite to stage pre-cast and pre-assembled components. Traffic could continue to use the existing bridge during most phases of construction, but a full closure would be required to remove the existing bridge and install the new deck.

Full bridge closure would affect daily traffic circulation and access as well as emergency services functions. Table C-1 provides a list of access needs across Lagunitas Creek Bridge and a range of potential conceptual solutions that could be incorporated into the project.


State Route 1 Lagunitas Creek Bridge Project C-2 Alternatives Analysis Report

Table C-1 Access Types and Range of Potential Conceptual Solutions

Access Type and Function Conceptual Solutions

Small Deliveries: Postal service, house-direct deliveries, small grocery deliveries, utilities meter reading FedEx, UPS, and other delivery services

• With wide announcements and frequent outreach, advertise the closure and provide instructions and wayfinding signage for detour route (see Figure C-1 below). Anticipate that many deliveries could be re-scheduled around the closure, but detour would be available if absolutely necessary. Distance between Pt. Reyes Station and Olema is 2.4 miles on SR 1 whereas detour would add approximately 7.1 miles.

• Postal Service, both deliveries and access to the Post Office would endure 9 extra miles for deliveries on either side of the Creek.

Large vehicle deliveries: Milk trucks, hay, etc.

• Many deliveries access Pt. Reyes Station either via Petaluma Highway/Pt. Reyes Road (or Lucas Valley Road to Point Reyes Road) or via Sir Francis Drake Blvd. for the Pt. Reyes National Seashore and Olema areas. If they had delivery destinations on both sides, they would have to use detour route and/or reschedule delivery times and days of delivery.

Emergency Service Access • Confirm that adequate emergency vehicles and personnel are available on either side of Lagunitas Creek (may need additional staff during closure)

• Volunteer fire departments would come from Bolinas, Inverness, and Lucas Valley

Farmer’s Market • Farmer’s market may experience reduced patronage during bridge closure although access via detour is still possible, unless closure was outside of the market season. Market is closed November 1 through April 30.

Equestrian access • Equestrian riders would not be able to ride their horses during bridge closure; riders would be asked to transport horses via car trailers during construction and closure.

Pedestrian/ bicycle access • Shuttle service may be provided to assist pedestrians and bicycles. Installing a temporary pedestrian/ bicycle bridge may not be possible during closure for safety purposes.

Grade-school access • School may be out of session during closure, therefore this may not be an issue.

• Summer camps and recreational programs like swimming lessons would need to be considered.

• Shuttle service may be needed if school is in session.

Tourism – April through October is high tourist season. Suggestion possible closure during November.

• Wayfinding signs for detour routes. Encourage access from Petaluma Highway for Pt. Reyes National Seashore and Access from Cotati for tourist points north.

• Place links to Caltrans site, providing bridge construction updates on all tourist websites.

• Social media could augment the status of the road closure and provide more information about the detour routes. Suggestions include: Twitter, WAZE, radio announcements, press releases, links on tourist web pages to daily updated SR 1 traffic map, linking Google earth maps with Caltrans information, etc.


State Route 1 Lagunitas Creek Bridge Project Alternatives Analysis Report C-3

Table C-1 Access Types and Range of Potential Conceptual Solutions

Access Type and Function Conceptual Solutions

Residents and local business workers

• Provide an on-call liaison to help troubleshoot unforeseen issues that arise.

• Daily notifications on progress, web cameras to help maintain interest and understanding about ABC and progress.

• Business workers: Use detour.

West Marin Stage Coach transit shuttle (Routes include Sir Francis Drake Boulevard, SR 1 and Bear Valley Road connecting Pt Reyes, Inverness, Bolinas)

• Additional service to make up for longer detour routes during the closure period. Another detour route would travel through.


State Route 1 Lagunitas Creek Bridge Project C-4 Alternatives Analysis Report

state route 1 lagunitas creek bridge project route 1 lagunitas creek bridge project alternatives...

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