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Section 2: Design - Highways and Roads

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Overview

This section builds upon the early phases described in Chapter 4 – Preliminary Engineering and Design and provides information on the design phase of highway and road construction projects. It provides a brief reference to items initiated in the 30 percent design and more details on items developed as the engineering progresses through final design. For all design elements, the LG and its design engineer must reference TxDOT’s guidance manuals (such as the Roadway Design Manual) or other TxDOT-approved manuals or standards to find details for incorporating TxDOT and Federal Highway Administration (FHWA) design requirements into the project design.

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Design Criteria

Chapter 4 – Preliminary Engineering and Design of the LGPP Manual contains a detailed discussion of the regulations and policies for design criteria used for highway and other construction projects. The same chapter of the LGPM Guide describes the practices for implementing established design criteria and the practices that must be followed if the local government (LG) desires to request an exception to the use of established design criteria. The design criteria selected by the LG must follow federal and state guidelines if state or federal funds are used or if the project is on the state highway system. In general, the LG must submit a design summary report to TxDOT, and TxDOT must assure the LG selects the proper functional classification and uses acceptable traffic data.

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Design Level of Service

The level of service (LOS) is a measure of traffic flow and congestion and should be used by the LG to design a project that will reasonably accommodate traffic. For projects on the state highway system or involving state or federal funding, the LG must request traffic data from TxDOT, select the LOS from the TxDOT Roadway Design Manual, develop a capacity analysis using the Highway Capacity Manual and submit to TxDOT for concurrence. The TxDOT district must review and approve the LG’s analysis and selected LOS. Chapter 4 – Preliminary Engineering and Design provides a detailed discussion of the LOS regulations and procedures.

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Hydraulic Design

General

Hydraulic structures must be designed to provide proper drainage for highways and roads. Guidelines for the design of hydraulic structures are contained in the TxDOT Hydraulic Design Manual.

Federal Requirements

  1. 23 CFR Part 650, Subpart A – Describes procedures for the location and hydraulic design of highway encroachments on flood plains.
    1. Minimum standards for hydraulic studies are listed.
    2. 23 CFR 650.115(a)(2) requires the design flood for encroachments by through lanes of interstate highways to not be less than the flood with a 2 percent chance of being exceeded in any given year (50-year design frequency).
    3. FHWA Additional Guidance on 23 CFR 650A, Attachment 2 (formerly the Federal-Aid Policy Guide Non-regulatory Supplement, Attachment 2) – Lists the procedures for coordinating highway encroachments on floodplains with the Federal Emergency Management Agency (FEMA).

State Requirements

  1. 43 TAC §§5.59, 15.56, 26.33 and 27.56 – Requires projects to be designed in accordance with TxDOT manuals, procedures, standards and guidelines. For regional mobility authority (RMA), toll and pass-through financed projects, preliminary design information must be sent to TxDOT for review and approval when the design is approximately 30 percent complete.

Required Practices

In general, the LG is responsible for selection of a design frequency for the drainage design of the roadway and is also responsible for coordinating floodplain management issues with FEMA and the local floodplain administrator. The LGPM Guide describes the required practices for hydraulic design.

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Longitudinal Barriers, including Bridge Rail

General

A barrier is the longitudinal system located on either bridges, medians or along the roadside used to shield vehicles from potential hazards or work areas. There is a national standard to assure only those barriers meeting certain crash test criteria are installed.

Federal Requirements

  1. 23 CFR 625.3(a)(1) – Provides projects on the national highway system to be designed and constructed to FHWA-approved standards. 23 CFR 625.3(d) states the standards are applicable regardless of the source of funds.
  2. 23 CFR 625.3(a)(2) – Requires federally funded projects not on the national highway system to be designed, constructed, operated and maintained in accordance with state laws, regulations, directives, safety standards, design standards and construction standards.

State Requirements

  1. 43 TAC §§5.59, 15.56, 26.33 and 27.56 – Requires projects to be designed in accordance with TxDOT procedures, standards and guidelines. For RMA, toll and pass-through financed projects, preliminary design information must be sent to TxDOT for review and approval when the design is approximately 30 percent complete.

Required Practices

The LGPM Guide provides the required practices and the LG and TxDOT responsibilities for the provision of longitudinal barriers for a road or highway project.

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Pavement Design

General

The proper design of a long-lasting pavement must be included in the overall project design in order to reduce pavement costs and future maintenance costs. Lower maintenance requirements also reduce road user costs by minimizing future lane closures for maintenance. TxDOT’s Pavement Design Guide provides pavement design methods and other standards.

Federal Requirements

  1. 23 CFR 626.3 – Requires pavements to be designed to accommodate current and predicted traffic needs in a safe, durable and cost-effective manner.
  2. FHWA Pavement Design Considerations (formerly Federal-aid Policy Guide Non-regulatory Supplement to 23 CFR Part 626) – Even though a particular pavement design procedure is not specified, each state is expected to use a design procedure appropriate for its conditions. The state may use the design procedures outlined in the “ AASHTO Guide for Design of Pavement Structures” or other pavement design procedures that, based on past performance or research, are expected to produce satisfactory pavement designs.

State Requirements

  1. 43 TAC §§5.59, 15.56, 26.33 and 27.56 – Requires projects to be designed in accordance with TxDOT manuals, procedures, standards and guidelines. For RMA, toll and pass-through financed projects, preliminary design information must be sent to TxDOT for review and approval when the design is approximately 30 percent complete.

Required Practices

In general, the LG must use standard pavement design methods approved by TxDOT. The LGPM Guide provides the required practices and responsibilities of each party for pavement design.

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Road Closure/Detour Plans

General

Construction often requires lane closures, detours or road closures. For all projects on the state highway system or impacting the state highway system, detours and closures must be coordinated with the entities responsible for both the road being detoured or closed and the road traffic is expected to use. Policies and procedures for the coordination of road closures and detours are described in the LGPM Guide.

Federal Requirements

  1. 23 CFR 630.1006 – Requires each state to implement a policy for the systematic consideration and management of work zone impacts on all federally funded projects.
  2. 23 CFR 630.1012 – Requires each project to have a transportation management plan or a traffic control plan. The plan must be consistent with Part 6 of the Manual on Uniform Traffic Control Devices and with the work zone hardware recommendations in the American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide.

State Requirements

  1. 43 TAC §15.56 – Requires projects to be designed in accordance with TxDOT procedures, standards and guidelines.

Required Practices

The LGPM Guide describes the TxDOT manuals and guidelines that must be used by the LG to coordinate road closures and detours on the state highway system or impacting the state highway system.

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Specifications/Special Provisions

General

Specifications are the directions, provisions and requirements outlining the description of work and the methods and manner the work is to be performed. Specifications and special provisions for highway and road projects are an integral part of the contract between the LG and the contractor. TxDOT maintains standard specifications, special specifications and required special provisions for use on road and highway projects in Texas.

Federal Requirements

  1. 23 CFR 630.205(b) – Requires plans and specifications to describe the location and design features and the construction requirements in sufficient detail to facilitate the construction and contract control of the project.
  2. 23 CFR 630.205(e) and 23 CFR 635.309(a) – Provides that FHWA authorization to advertise for receipt of bids will not be given until the plans, specifications and estimate (PS&E) have been approved.
  3. 23 CFR 635.411 – Prohibits referencing proprietary materials in the specifications unless supported by an approved public interest finding.
  4. FHWA Guidelines for Preparation of Plans, Specifications and Estimates (formerly the Federal-aid Policy Guide Non-regulatory Supplement to 23 CFR Part 630 Subpart B) – Contains guidelines for the preparation of the PS&E and definitions for standard specifications, special specifications and special provisions. NOTE: FHWA approves the use of TxDOT standard specifications, special specifications and special provisions on federally funded projects.

State Requirements

  1. 43 TAC §15.56 – Requires the use of the latest TxDOT standard specifications, special specifications and special provisions for projects on the state highway system. In addition, it requires all PS&E to be approved by the department prior to advertisement for bids on the project. If the LG desires to propose alternate specifications for a project on the state highway system, it may request TxDOT approval of alternate specifications for:
    1. projects with a pass-through financing arrangement ( 43 TAC §5.59);
    2. regional mobility authority projects connecting to the state highway system ( 43 TAC §26.33); and
    3. toll projects ( 43 TAC §27.56).

Required Practices

In general, the LG must either adopt the latest TxDOT standard specifications, applicable special specifications and required special provisions or request TxDOT approval of alternate, equivalent specifications. The LGPM Guide provides a detailed description of the required practices for developing specifications that must be used by the LG in order to obtain approval by TxDOT.

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