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Section 2: Considerations Based on Bridge Location

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Highway Grade Separations

A highway grade separation is a bridge that carries vehicular traffic over vehicular traffic. This type of structure is often referred to as an overpass or an underpass. For proper nomenclature of an overpass or underpass, refer to the Bridge Detailing Guide. These structures allow the highway to safely accommodate high volumes of traffic through intersections. Some controlling factors in the planning of a highway grade separation include highway geometry and the available right of way.

Visual distractions on a highway are hazards. For this reason, the grade separation structure should conform to the highway alignment and cross section. Limit its profile to grades that allow sufficient stopping sight distance. The transition from roadway to grade separation should be designed such that the driver’s behavior is not altered by erratic changes.

The availability of adequate right-of-way may limit the possible structure types and construction processes, which can lead to increased costs. Stage construction may be required in locations with inadequate right-of-way. Additionally, considerations such as span lengths, soil characteristics, and skew may also affect the structure’s design.

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Structures over Streams

Bridges and culverts carrying vehicular traffic over a body of water are considered hydraulic highway facilities. When planning a structure over a body of water, consider each related hydraulic facility in the project as part of a total system conveying water. Related hydraulic facilities can include open channels, storm sewers, pump stations, and some reservoirs. See the Hydraulic Design Manual for discussions of hydraulic facilities.

Plan hydraulic facilities early in project development to uncover unusual problems that may become much more difficult to address at later stages. Early planning is particularly important with respect to highway location. Navigable stream and wetland crossings require permits from the U.S. Army Corps of Engineers (USACE) and the U.S. Coast Guard (USCG). Agreements must often be executed for storm sewer projects; facilities associated with reservoirs may also require special attention.

Culverts are closed conduits, usually with fixed flow lines, that can operate either under pressure or with a free surface flow. Bridges, as opposed to culverts, are not considered closed conduits. The flow line of a bridge is rarely fixed and the material along the flow line of a bridge is usually the same as the stream it crosses. Hydraulic considerations for bridges are discussed in Chapter 8 of the Hydraulic Design Manual. Preliminary design criteria for bridges over streams are discussed in Preliminary Design Features -- Features Based on Bridge Location, in Chapter 3 of this manual.

All culverts are designed similarly regardless of whether they exceed the 20-ft. length along the roadway centerline that causes them to be classified as bridges. Hydraulic considerations for culverts are discussed in Chapter 7 of the Hydraulic Design Manual. Acceptable types of culverts include the following: cast-in-place concrete box, precast concrete box, full-circle or elliptical pipe, pipe arch, structural plate, or approved long span culverts. Material for pipe, pipe arch, and elliptical shapes include steel, aluminum, aluminized steel, and concrete. Materials for structural plate and long span culverts may be galvanized steel or aluminum. General design criteria for culverts are discussed in Preliminary Design -- Features Based on Bridge Location in Chapter 3, of this manual.

Bridges and culverts are vulnerable to damage from flood related causes. To minimize the risk of damage, recognize and consider the hydraulic requirements of a stream crossing in all phases of project development, construction, and maintenance. Hydrologic and hydraulic analyses, including a scour analysis, are required for all new bridges over waterways, bridge widening, bridge replacement, and roadway profile modifications that may adversely affect the flood plain, even if no structural modifications are necessary. See Title 23 Code of Federal Regulations (CFR) Subpart C in conjunction with FHWA Technical Advisory T 5140.23, Scour at Bridges, for more information on this federal policy.

Hydrologic and hydraulic analyses typically include the following:

The thoroughness of a hydrologic and hydraulic study will depend upon the nature of the stream. After the study is completed, each district maintains the complete hydrologic and hydraulic design data for all waterway crossings. The scour report should also be added to the Bridge Inspection Database under the corresponding National Bridge Inventory (NBI) number. This complete file could include the following:

Show pertinent hydrologic and hydraulic design data for bridges, culverts, and storm sewers in the plans rather than on separate calculation sheets submitted with the plans, specifications, and estimates (PS&E) in order to facilitate review of the PS&E and assure a permanent record. Minimum requirements for these data can be found in the Hydraulic Design Manual. Bridge layout requirements of hydrologic and hydraulic design information can be found in the Preliminary Layout Approval Process in Chapter 5 of this manual.

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Highway-Railroad Grade Separations

Highway structures that carry vehicular traffic over railroad traffic are referred to as railroad overpasses. Conversely, railroad underpasses are structures that pass vehicular traffic under railroads. Some concerns when planning a railroad overpass or underpass include the selection of the structure type, the horizontal and vertical clearance to the centerline of the track, the available right-of-way, drainage, train movements, skew angle, and the time required in coordinating with the railroad company.

The selection of the type of structure, either overpass or underpass, usually depends on the existing topographical conditions. Railroad underpasses present drainage problems, sometimes requiring the use of pump stations. Pump stations are very expensive and require maintenance for the life of the facility. Accordingly, avoid pump stations unless absolutely necessary. Railroad underpass construction also requires railroad shoofly construction to temporarily move the tracks while the bridge construction is completed. Shoofly construction is expensive and should be used only when necessary. Underpasses also reduce the flexibility to widen the roadway in the future. This construction type can be complex and increase the review time by the railroad. The timeframe for an overpass agreement to be executed is generally 12 to 18 months. An underpass agreement will take a minimum of 24 months.

Proper clearances are an important consideration in the early planning phase. In order to determine vertical clearance, it is important to determine the top of the highest rail elevation on the track for approximately 1,000 ft. in each direction from the roadway and for a greater distance if a change in railroad grade is proposed. If the railroad is on a curve, take the profile along the highest rail elevation on the track for overpasses, and along the lowest rail elevation on the track for underpasses. Include this information in Railroad Exhibit A, described below.

Railroad Exhibit A is included in the agreement that must be negotiated between TxDOT and the railroad company. Requirements for the preparation of Railroad Exhibit A, as well as the policy and practices concerning highway-railroad grade separation structures, can be found in the Rail-Highway Operations Manual. Some railroad companies may have additional requirements for Railroad Exhibit A. The railroad company reviews Railroad Exhibit A for its preliminary review of the bridge project. The Traffic Operations Division’s Rail Safety Section (TRF-RSS) is the sole point of contact and Office of Primary Responsibility for all matters relating to agreements with the railroad companies. Submittal of all Exhibits needed in the execution of the various types of railroad agreements, including Exhibit A drawings for structures, must be coordinated through TRF-RSS. The District office submits Railroad Exhibit A drawings to TRF-RSS at least 12 months prior to the scheduled contract letting date to allow adequate time for negotiations and processing with the railroad company. Exhibits B are only needed for Railroad Underpass projects.

Examples of PS&E and Exhibit A and B submittals can be found at the following location: www.txdot.gov/inside-txdot/division/traffic.html and http://crossroads/org/TRF/_includes/documents/5-Sample_Exhibit_B.pdf, respectively. If you need assistance accessing the second link, which is internal to TxDOT, please contact the TxDOT District office with which you are working, or the Bridge Division project manager.

Railroads can have significant effects on a project, from design to construction. Railroad companies may require spans to be long enough to span the entire right-of-way to avoid adversely affecting train movements, and lack of usable right-of-way may necessitate stage construction. When possible, span the entire railroad right-of-way to alleviate railroad concerns regarding effects on train movements.

Railroad companies may object to the use of their right-of-way if it adversely affects train movements, which can have significant effects on project design. Spans may need to be long enough to span railroad right-of-way, and staged construction may be required due to the lack of usable right-of-way. In addition, special design requirements may be required to prevent runoff from draining onto railroad right-of way. Train movements can also affect the construction process. Address construction schedule and construction crew safety during the preliminary design phase. When possible, span the entire railroad right-of-way.

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Pedestrian Bridges

Pedestrian bridges carry pedestrian traffic over an obstacle, usually vehicular traffic. The need for a pedestrian crossing is the major preliminary consideration. Consider preliminary design features such as vertical and horizontal clearance as well as pedestrian ramp approaches. Pedestrian bridges may be constructed of structural steel, reinforced concrete, prestressed concrete, or other suitable materials. Aesthetics are especially important in these structures because they are subject to public view from all sides and are usually unique within a neighborhood area.

Pedestrian structures under the roadway are discouraged unless the highway lanes are on a fill of 15 ft. or more. This type of structure presents problems of drainage and lighting and creates a condition where policing is difficult.

Additional information on Americans with Disabilities Act (ADA) and Texas Accessibilities Standards (TAS) requirements can be found in Chapter 2 of the Roadway Design Manual. However, always refer to the current Americans with Disabilities Act Accessibility Guidelines (ADAAG) and Texas Accessibility Standards for complete ADA and TAS requirements.

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Historically Significant Bridges

Historically significant bridges are listed or eligible to be listed in the National Register of Historic Places. These bridges can be either on-system or off-system. Projects involving historic bridges involve many issues that must be resolved. These issues are discussed in further detail in the Historic Bridge Manual.

Contact the Bridge Division project manager as early as possible when historic bridge projects are involved. Some important considerations concerning historic bridge projects include coordination with other divisions, coordination with federal and state agencies, and the project letting schedule. TxDOT is required to allow the State Historic Preservation Officer (SHPO) of the Texas Historical Commission 30 days to review the final plans, specifications and estimates (PS&E) for all projects involving historic structures. Therefore, allow additional processing time for historic preservation projects. Contact the Environmental Affairs Division early in the process to give architectural historians time to schedule and perform surveys. Keep in mind that these projects can be environmentally cleared and approved for letting only after all SHPO comments have been addressed and incorporated into the final PS&E package.

TxDOT has developed minimum design criteria for off-system historically significant bridges. TxDOT also has developed specific procedures for the coordination of projects concerning historic bridges. These procedures can be found in the Historic Bridge Manual.

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International Bridges

Consider the following aspects when planning an international bridge:

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  • The Texas Transportation Commission must approve an international bridge application.
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  • A Presidential Permit must be acquired.
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  • The International Boundary and Water Commission must approve the project.
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  • Coordination is necessary with Mexican governmental agencies, designers, and contractors.

Section 201.612 of the Texas Transportation Code requires an entity authorized to construct or finance the construction of an international bridge over the Rio Grande to obtain approval from the Texas Transportation Commission (Commission) prior to seeking a Presidential Permit for construction. Title 43 TAC, Sections 15.70-15.76, specifies the process by which applicants submit an application.

Departmental Procedures. In order to comply with the rules requiring approval by the Texas Transportation Commission of an international bridge prior to requesting a Presidential Permit and to provide the 120-day response time required by legislation, TxDOT has designated the Transportation Planning and Programming Division (TPP) as the department liaison for international bridge applications. TPP has responsibility for providing findings and recommendations to the Commission. Aiding TPP in this responsibility will be the Bridge Division, the Environmental Affairs Division, the Financial Management Division, the Right-of-Way Division, and TPP’s Freight Plan/International Trade Section. They will assist TPP in determining if an application is complete and provide subject matter expertise in analyzing the applications and providing recommendations to the Commission.

TPP provides the application form to applicants when requested. TPP then, immediately upon receipt of an application and the requisite 20 copies, date-stamps the application and copies; forwards one copy of the application to the designated points of contact in the Bridge Division, Environmental Affairs Division, Financial Management Division, Right of Way, and TPP’s Freight Plan/International Trade Section; and sets a ten-working-day deadline from the date stamp for the division points of contact to determine if the application is complete.

NOTE: All subsequent references to “the date stamp” refer to the TPP date stamp specified in the preceding sentence.

If the application is incomplete, TPP will return all copies with a written response specifying deficiencies. When it determines that an application is complete or that a resubmitted application is no longer deficient, TPP will notify the applicant and the Governor’s Office in writing that the application meets the requirements of Title 43 TAC, Section 15.74 and begins the analysis.

Division Responsibilities. TPP will take the following actions:

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  • Send a copy of the application to the Department of Public Safety, the Texas Commission on Environmental Quality (TCEQ), the Department of Agriculture, the Historical Commission, the Alcohol Beverage Commission, the Department of Commerce, and local government entities (county and municipal) where applicable, requesting comments be returned within 20 working days from receipt at the Governor’s Office.
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  • Send a copy of the application to the Governor’s Office, requesting comments be returned within 20 working days from receipt at the Governor’s Office.
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  • Request analysis and the written results of that analysis from each division and special office named above within 45 days of the date stamp.
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  • Send an application to and request analysis and the written results of the analysis from the appropriate district(s) and metropolitan planning organization(s) (MPOs). Application and results of analysis must be returned to TPP within 20 working days of receipt at the district or organization.
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  • Coordinate with the Office of General Counsel (OGC) to schedule, advertise, and conduct public hearings within 45 days of the date stamp.
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  • Compile and summarize public hearing comments within 65 days of the date stamp.
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  • Analyze compliance with the state transportation plan and, if appropriate, with the regional transportation plan developed by the MPO having jurisdiction over the project within 65 days of the date stamp.
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  • Compile and summarize responses from state agencies, divisions, district(s), MPOs, and local government entities within 65 days of the date stamp.
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  • Prepare and send staff response, along with recommendation for the Transportation Commission action, to the executive director through the deputy executive director/chief engineer.
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  • Coordinate with OGC to prepare documents and include on the Transportation Commission meeting agenda recommended action no later than 120 days from the date stamp (the Commission must act within 120 days of the date stamp).
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  • Notify the applicant and Governor’s Office in writing of the Transportation Commission action within two working days after the Commission meeting.

The Bridge Division will:

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  • Provide a primary and an alternate point of contact for analyzing international bridge applications.
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  • Upon receipt of an application from TPP, screen applicable sections for completeness and respond in writing to TPP no later than ten working days from the date stamp.
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  • Upon receipt of TPP request, analyze the design portion of the application to ensure bridge and roadway are designed to accepted standards and specifications.
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  • Provide written analysis and recommendations to TPP no later than 45 days from the date stamp.
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  • Assist TPP in preparing for the Transportation Commission meeting.
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  • Coordinate with the Design Division.

The Financial Management Division will:

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  • Provide a primary and an alternate point of contact for analyzing international bridge applications.
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  • Upon receipt of an application from TPP, screen applicable sections for completeness and respond in writing to TPP not later than ten working days from the date stamp.
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  • Upon receipt of TPP request, analyze the financial portion of the application.
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  • Provide written analysis and recommendations to TPP not later than 45 days from the date stamp.
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  • Assist TPP with preparing the Transportation Commission meeting.

The Environmental Affairs Division will:

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  • Provide a primary and an alternate point of contact for analyzing international bridge applications.
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  • Upon receipt of an application from TPP, screen applicable sections for completeness and respond in writing to TPP not later than ten working days from the date stamp.
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  • Upon receipt of TPP request, analyze the environmental portion of the application to ensure environmental considerations have been addressed or mitigated.
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  • Provide written analysis and recommendations to TPP not later than 45 days from the date stamp.
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  • Assist TPP with preparing for the Transportation Commission meeting.

The Right of Way Division will take the following actions:

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  • Provide a primary and an alternate point of contact for analyzing international bridge applications.
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  • Upon receipt of an application from TPP, screen applicable sections for completeness and respond in writing to TPP not later than ten working days from the date stamp.
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  • Upon receipt of TPP request, analyze the design portion of the application to insure right-of-way issues have been adequately addressed.
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  • Provide written analysis and recommendations to TPP not later than 45 days from the date stamp.
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  • Assist TPP with preparing for the Transportation Commission meeting.

TPP’s Freight Plan/International Trade Section will:

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  • Provide a primary and an alternate point of contact for administrative and protocol coordination with Mexican officials and entities concerning international bridges and for analyzing international bridge applications.
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  • Provide to divisions the review, comment, and analysis of any politically sensitive issues, protocol considerations, or other factors related to any Mexican documents or data submitted as part of an application.
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  • Upon receipt of TPP request, analyze the written commitments from Mexican federal, state, and local jurisdictions concerning their abilities to provide necessary transportation infrastructure.
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  • Provide a written analysis and recommendations to TPP not later than 45 days from the date stamp.
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  • Assist TPP with preparing for the Transportation Commission meeting.
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Bridges with Adjacent States

In crossings of the Red River and the Sabine River where they form the boundaries between Texas and Oklahoma, Arkansas, Louisiana, or New Mexico, the Bridge Division project manager serves as negotiator for necessary agreements between the states.

The design, construction, and maintenance of each bridge are the responsibility of Texas or the bordering state. The responsible state for each bridge is shown in Table 4.1.

Anchor: #CIHFFBJFTable 4-1: Responsibility for Bridges with Adjacent States

Responsible State

Location

Highway

TX District

AR District

LA District

OK District

Texas

New Boston/Forman

TX 8/AK 41

ATL

03

 

 

Texas

Joaquin/Logansport

US 84

LFK

 

04

 

Texas

Toledo Bend Reservoir

TX 21/LA 6

LFK

 

08

 

Texas

Burkville/Burr Ferry

TX 63/LA 8

BMT

 

08

 

Texas

Orange/Vinton

IH 10

BMT

 

07

 

Texas

Sabine Lake

TX 82/LA 82

BMT

 

07

 

Texas

Oklaunion/Davidson

US 183

WFS

 

 

05

Texas

Burkburnett/Randlett

IH 44/US 277/281 NB

WFS

 

 

07

Texas

Gainesville/Marietta

US 77 NB & SB/IH 35

WFS

 

 

07

Texas

Denison/Durant

US 75 NB & SB

PAR

 

 

02

Texas

Clarksville/Idabel

TX 37

PAR

 

 

02

Texas

Illinois Bend/Courtney

TX FM 677/OK SH 89

WFS

 

 

07

Texas

Dekalb/Harris

US 259

ATL

 

 

02

Arkansas

Texarkana/Ashdown

US 59 SB

ATL

03

 

 

Louisiana

Newton/Merryville

US 190

BMT

 

07

 

Louisiana

Deweyville/Starks

TX 12/LA 12

BMT

 

07

 

Oklahoma

Quanah/El Dorado

TX 6/OK 6

CHS

 

 

05

Oklahoma

Burkburnett/Randlett

IH 44/US 277/281 SB

WFS

 

 

07

Oklahoma

Clay/Waurika

TX 79/OK 79 (Main)

TX 79/OK 79 (Relief)

WFS

 

 

07

Oklahoma

Ringgold/Terral

US 81

WFS

 

 

07

Oklahoma

Whitesboro/Madill

US 377

PAR

 

 

02

Oklahoma

Vernon/Altus

US 283

WFS

 

 

05

Oklahoma

Bonham/Durant

TX 78/OK 78

PAR

 

 

02

Oklahoma

Paris/Hugo

US 271 NB & SB

PAR

 

 

02

Oklahoma

Grayson/Bryan

Carpenter’s Bluff (Off)

PAR

 

 

 

Oklahoma

2.8 mi N of FM 680

Hollis Rd (Off)

CHS

 

 

 

NB = Northbound

SB = Southbound

Off = Off-System



Although each state is responsible for a specific bridge, the costs for design, construction, and maintenance are shared between the two states. The cost of the bridge approaches, however, is the responsibility of the state in which they are located.

The responsible state prepares the PS&E, processes the letting of the project for construction, and provides routine and major maintenance for the bridge after it is constructed. Each state shares in 50% of the cost of design, construction, and major maintenance expenses.�

Planning a bridge project with an adjacent state requires the following actions in this sequential order:

General Information. The project must meet federal requirements if federal funds are used to finance the project.

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  • The project must be on the State Transportation Improvement Plan (STIP) of each state.
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  • The project must be on the Unified Transportation Program (UTP).
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  • A Commission minute order authorizing the State of Texas to enter into an agreement with another state is necessary whenever a bridge is constructed on new location, when a bridge is being replaced, or when a major rehabilitation project (such as redecking or widening) is planned.

Agreement. An agreement between the responsible state and the partner state is required prior to beginning planning for construction of a new bridge at a new location, for replacing an existing bridge, or for conducting a major rehabilitation such as redecking or widening. No agreement is required for maintenance contracts. The responsible state for each bridge located on the border between Texas and another state is defined in Table 4-1.

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  • The Bridge Division project managers coordinate the negotiations with the other state and prepare and process the agreement for execution when Texas is the responsible state.
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  • As stated in the TAC Title 43, Part 1, Chapter 15, Subchapter E, Rule 15.55, for off-system bridges, local cost participation is not required for a bridge connecting Texas with a neighboring state.
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  • The governor of Texas must execute all bridge project agreements between Texas and another state.

Plan Development. The responsible state (Table 4-1) will prepare preliminary and final plans, specifications, and estimates of cost subject to the approval of the State of Texas and FHWA.

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  • Each state will pay one-half of the cost of the bridge, as well as the full amount of its respective approach roadway costs on its respective side of the state line.
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  • A separate control-section-job (CSJ) number for the bridge and each approach (three total) is required.
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  • For federally funded projects with state oversight, a Federal Project Authorization and Agreement (FPAA) must be signed before obligation of preliminary engineering funds.
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  • Each state will, at no cost to the other state, secure necessary right-of-way, relocate all utilities, and identify and remove all known hazardous materials to accommodate that portion of the project on the respective side of each state.
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  • Bank protection, jetties, or similar work required to protect the bridge or its approaches or to hold the river channel to its present course will be considered as a part of maintenance of each bridge, whether such work may be located wholly in one state or the other.
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  • The project must be environmentally cleared.

Letting. The responsible state (Table 4-1) prepares the PS&E, processes the letting of the project for construction, and provides routine and major maintenance for the bridge after it is constructed.

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  • For federally funded projects with state oversight, a Federal Project Authorization and Agreement (FPAA) must be signed before obligation of project funds. In addition, a state Letter of Authority (LOA) must be signed before letting. For federally funded projects with federal oversight, each state must obtain its own LOA from Federal Highway Administration (FHWA) and provide participating adjacent states with a copy at least three weeks before letting.
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  • Any prospective bidder who is qualified under the requirements of either state will be considered by the other state as being qualified and eligible to bid on the project and will be provided with proposals upon request.
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  • At a time to be agreed upon by the parties, and subject to the approval of FHWA, the project shall be publicly advertised for bids. The project must be advertised in accordance with federal requirements as well as the laws of both states. Each state shall issue public notice of advertisement that bids are to be received on the project. The responsible state shall provide the adjacent state with a copy of the legal advertisement the number of days specified in the agreement prior to the proposed letting date for publishing in the state official journal.
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  • Copies of the bid tabulations for all bids received shall be provided to the adjacent state for review.
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  • Both the Texas Transportation Commission and the highway authority of the other state must approve award of the contract.

Construction. The responsible state (Table 4-1) prepares the PS&E, processes the letting of the project for construction, and provides routine and major maintenance for the bridge after it is constructed.

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  • The adjacent state will reimburse the responsible state for the design costs and engineering costs for the adjacent state’s share on a monthly progressive estimate basis expressed in certified invoices furnished by the responsible state.
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  • All invoices received by the TxDOT will be directed to the respective TxDOT Area Engineer (AE) for review of work progress.
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  • The responsible state will transmit to the State of Texas appropriate documentation of the services provided by the responsible state. Funds requested from the State of Texas for services provided by responsible state shall be made available within 30 days from receipt of the request.
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  • Once approved by the TxDOT AE, the invoice will be sent to the Financial Management Division for processing.
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  • The construction contract and required personnel for all construction engineering and supervision will be administered by the responsible state.
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  • Final acceptance of the project shall be subject to both states.

Post-Construction. After completion of the project, it shall be operated and maintained by both states for use by the public without charge or toll.

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  • Each party shall maintain the roadway approaches to its respective end of the bridge.
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  • Each state shares in 50% of the cost of design, construction, and major maintenance expenses, except that each state is 100% responsible for costs associated with design, construction, and maintenance of the respective bridge approaches of each state. The responsible state provides routine maintenance at no cost to the other state. “Routine maintenance” is defined as maintenance cost that is less than $5,000. “Major maintenance” is defined as maintenance cost that is $5,000 or more; or as defined in the agreement. The responsible state must contact the other state for its concurrence before performing any major maintenance work.
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Federally Funded Off-System Bridges

As a rule, off-system bridge projects administered by TxDOT have federal fund participation. Most of these projects consist of replacement or rehabilitation of structurally deficient or functionally obsolete deficient bridges funded with a combination of federal-local or federal-state-local funds, with the federal funds from the Highway Bridge Program. However, TxDOT does administer a relatively small number of other off-system bridge construction projects with federal funding from the Surface Transportation Program (STP).

Coordinate with the local government when planning off-system bridge projects, particularly when using funds from the Highway Bridge Program. An appropriate agreement between the State and local government must be executed before any work can be performed on an off-system project funded from the Highway Bridge Program. In addition to specifying the responsibilities of the two parties in the performance and funding of the work, the agreement provides for advance payments by the local government of its share of the project funding responsibilities. The agreement also allows a local government to use equivalent-match projects as payment toward its share of project funding.

The current standard agreements may be obtained from the Contracts and Purchasing Division’s standard contracts web page at the following link (internal to TxDOT): http://crossroads/org/GSD/Contract%20Services/Standard%20Contracts/default.htm. If you need assistance accessing this web page, which is internal to TxDOT, please contact the TxDOT District office with which you are working, or the Bridge Division project manager. Title 43 TAC, Sections 15.52 and 15.55 provides more information about the Off-State System Highway Bridge Program agreements and cost participation.

Off-system bridges with adjacent states are funded 100% by a combination of federal and state funds, or 100% by state funds. No local government contribution on the Texas side of the bridge is required.

See Chapter 3 of this manual for more information regarding the administration of off-system bridge projects.

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Interchanges

An interchange is a system of connecting roadways, including one or more grade separation structures, which allows uninterrupted movement of traffic between two or more roadways, generally highways.

Planning considerations concerning interchanges include those considered for highway grade separation structures. The type of interchange to use is also a major consideration. Selection of interchange type is a matter of roadway design and is influenced by factors such as the existing terrain, availability of right of way, cost, and roadway classification, among other considerations. Common types of interchanges, as well as suggestions on their use, are covered in Chapter 3 of the Roadway Design Manual. AASHTO’s “A Policy on Geometric Design of Highways and Streets” also discusses interchanges.

Additional time is required to review plans for interchange projects because of the complicated features, which can include aesthetics. In order to ensure that the preliminary bridge layout contains the appropriate level of detail, and to maintain the letting schedule, always refer to the Preliminary Bridge Layout Review Process in Chapter 5 for bridge layout information and the Table 6-1 Submission Schedule in Chapter 6 for appropriate lead times.

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Overhead Sign Supports

Do not locate overhead sign supports on bridges, if possible. If such location is required, indicate on the bridge layouts a cantilever-type overhead sign support (COSS) founded on a bent cap or on an isolated concrete column on drilled shaft, or an overhead sign bridge (OSB) attached directly to the bridge superstructure. The location of any overhead sign support on bridges requires special design by the Bridge Division.

If overhead support for a dynamic message sign (DMS) is required, determine the appropriate DMS type and its attachment details before completing the detailed project design. Consider whether walkways or light fixtures are required. Configure the DMS on the truss to minimize the horizontal offset between the DMS and the truss. Mount the DMS on a Balanced Tee-type COSS or on an OSB. Do not mount the DMS on a single cantilever-type COSS. Mounting a DMS on an OSB requires a special OSB design by the Bridge Division in addition to the attachment design required if the DMS is to extend over a bridge.

Position sign support brackets for retrofit of signs along existing rails at bridge overpasses such that the bottom edge of the sign panel and support bracket do not encroach on the existing vertical clearance of the bridge.

Do not mount a closed circuit television (CCTV) on a tube protruding from an OSB or a COSS because of wind or traffic-induced vibrations. These vibrations may be more pronounced when the OSB or COSS is mounted directly to a bridge superstructure.

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Utility Structures

Interstate Highways. Where it would be more economical to carry utility lines across a freeway in a tunnel or on a bridge rather than in separately trenched and encased crossings, provide a separate structure for the utility crossing. Such a structure may serve a joint purpose as a utility and pedestrian facility and/or sign support. In providing a utility tunnel or bridge, the following conditions should be met:

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  • Isolate mutually hazardous transmittants, such as fuels and electric energy, by compartmentalizing or by auxiliary encasement of incompatible carriers.
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  • Conform the utility tunnel or utility bridge structure design, appearance, location, bury, earthwork, and markings to the culvert and bridge practices of the department.
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  • Where a pipeline on or in a utility structure is encased, the casing must be effectively opened or vented at each end to prevent possible build-up of pressure and to detect leakage of gases or fluids.
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  • Take additional protective measures where a casing is not provided for a pipeline on or in a utility structure, such as employing a higher factor of safety in the design, construction, and testing of the pipeline, than would normally be required for cased construction.
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  • Communication and electric power lines must be suitably insulated, grounded, and preferably carried to a manhole located beyond the backwall of the structure. Insulate carrier and casing pipe from electric power line attachments.
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  • Install shut-off valves, preferably automatic, in lines at or near ends of utility structures unless segments of the lines can be insulated by other sectionalizing devices within a reasonable distance.
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  • Utility companies must agree that any maintenance, servicing, or repair of the utility lines will be their responsibility.

Non-interstate Highways. If utility lines have their own easement and it would be more economical to the department, adjust the lines across a highway by use of a utility tunnel or bridge. Where the utility lines are on a public right-of-way by sufferance and the adjustment of the utility is the sole responsibility of the private or public utility company, the department may permit the provision of a utility structure without cost to the department provided the same conditions outlined for Interstate Highways and all other pertinent requirements are met. If a structure is to serve as a joint utility-pedestrian crossing or a joint utility-sign support structure, the department will participate to the extent necessary for accommodation of pedestrians and highway signs only.

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