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Design

 

Guidance on NHS Design Standards and Design Exceptions

With the implementation of the MAP-21 legislation and the resulting changes to highways included in the National Highway System (NHS), the need has arisen to address how to apply our design standards and design exceptions in the development of highway improvement projects.

While FHWA-approved standards apply to all projects on the NHS, we encourage flexibility and a context-sensitive approach which considers the full range of project needs and the impacts to the community and natural and human environment. Design exceptions are a useful tool that may be employed to achieve a balance of project needs and community values. State DOT or local authorities must evaluate, approve, and document design exceptions. Approving any design exception is a Federal Action, which requires reviewing and documenting their potential environmental impacts.

For highways added to the NHS under MAP-21, the effective date that projects are required to comply with the NHS design requirements and standards is October 1, 2012. NHS projects having completed an environmental decision or final design prior to that date may proceed without changes. NHS projects completed on or after that date must follow the FHWA-approved standards or receive approval for design exceptions.

Additional information on MAP-21 legislation is available at: http://www.fhwa.dot.gov/map21/qandas/. We encourage you to review this information and share it with your State and local partners.

  1. Are there design standards that apply to the National Highway System (NHS)?
  2. What design standards has FHWA adopted?
  3. Do FHWA-adopted design requirements apply to all projects on the NHS?
  4. Do NHS standards apply to projects that do not use Federal-Aid Highway Program (FAHP) funding?
  5. What flexibilities are allowed with NHS design standards?
  6. Can projects on the NHS deviate from the NHS design standards?
  7. What justification is required to evaluate, review, and approve design exceptions on the NHS?
  8. Are design exceptions approved on a project-by-project basis?
  9. At what point in the development of a project should design exceptions for a project on the NHS be reviewed and approved?
  10. What variances from NHS standards require FHWA review and approval of design exceptions?
  11. Who approves design exceptions for projects on the NHS?
  12. Does a State DOT or local agency's approval of design exceptions on behalf of FHWA constitute a Federal Action?
  13. Do design exceptions meet the criteria to be classified as a Categorical Exclusion (CE)?
  14. What information must State DOTs or local agencies review to determine if a proposed design exception can be classified as a CE?

  1. Are there design standards that apply to the National Highway System (NHS)?

    Yes.  The Federal Highway Administration (FHWA) has adopted design standards for the NHS (as specified in 23U.S.C.109(c)).

  2. What design standards has FHWA adopted?

    The FHWA has adopted standards for roadway geometrics, bridges and structures, erosion and sediment control, hydraulics, traffic noise, materials, and accessible pedestrian design. These standards are listed in 23CFR625.4 and 49CFR37.9.

  3. Do FHWA-adopted design requirements apply to all projects on the NHS?

    Yes.  The FHWA-adopted design requirements found in 23CFR625 and 49CFR37.9 apply to projects on the NHS, including routes added to the NHS by the Moving Ahead for Progress in the 21st Century Act (MAP-21).

    The FHWA-adopted geometric design standards apply to new and reconstruction projects on the NHS.  The NHS standards for the geometric design of highways include the American Association of State Highway and Transportation Officials' (AASHTO) A Policy on Design Standards Interstate System (January 2005) and A Policy on Geometric Design of Highways and Streets (2011).

    For resurfacing, restoration, and rehabilitation (3R) projects, design standards adopted by the State Department of Transportation (DOT) and approved by the FHWA Division Administrator will apply (23CFR625.4(a)(3)). More information about developing geometric design standards for 3R projects is available in the Transportation Research Board publication Designing Safer Roads: Practices for Resurfacing, Rehabilitation, and Restoration and the FHWA Technical Advisory Developing > Geometric Design Criteria and Processes for Non-freeway RRR Projects.

  4. Do the NHS design standards apply to projects that do not use Federal-Aid Highway Program (FAHP) funding?

    Yes. These FHWA-adopted or approved design standards apply to all street and highway projects on the NHS, regardless of the funding source for the project. (23CFR625.3).

  5. What flexibilities are allowed with NHS design standards?

    The NHS geometric design standards provide a range of acceptable values for highway features and FHWA encourages the use of this flexibility to achieve a design which best suits the desires of the community while satisfying the purpose for the project and needs of its users.

    Design values should be selected based on an evaluation of the context of the facility, needs of all the various project users, safety, mobility (i.e., traffic performance), human and natural environmental impacts, and project costs.  For most situations, there is sufficient flexibility within the range of acceptable values to achieve a balanced design. However, when this is not possible, a design exception may be considered and be appropriate.

    In addition, section 1404(b) of the Fixing America's Surface Transportation Act (FAST Act) creates an exception to current FHWA regulations at 23CFR 625governing the design standards for all NHS highways, providing some local jurisdictions with additional flexibility in the choice of design standards for specific projects. Refer to separate Questions & Answers specific to the provisions of section 1404 of the FAST Act, available at http://www.fhwa.dot.gov/programadmin/standards.cfm.

  6. Can projects on the NHS deviate from the NHS design standards?

    Yes. State and local agencies may consider designs that deviate from the NHS design standards when warranted based on the conditions, context, and consequences of the proposed projects.  If an agency chooses to deviate from a standard, they must document the design exception. (23CFR625.3(b)).

    A design exception states the reason(s) for a specific deviation from an established standard for a specific highway feature and may also include features to mitigate any negative effects. For additional information on design exceptions, please refer to the FHWA publication Mitigation Strategies for Design Exceptions.

  7. What justification is required to evaluate, review, and approve design exceptions on the NHS?

    All proposed design exceptions should be thoroughly analyzed and the potential impacts understood before approval. The process to evaluate and justify design exceptions must be based on an evaluation of the context of the facility (e.g., community values), needs of all the various project users, safety, mobility (i.e., traffic performance),  human and environmental impacts, project costs, and other impacts.  As codified in 23 CFR 625.3(f), exceptions may be approved on a project basis for designs that do not conform to the minimum or limiting criteria set forth in the standards, policies, and standard specifications adopted in 23 CFR 625.  Design exceptions, subject to approval by FHWA, or on behalf of FHWA if a State transportation agency has assumed the responsibility through a Stewardship and Oversight agreement, are required for projects on the NHS only when the controlling criteria are not met (see Question #10).

    Documentation for design exception requests should describe all of the following:

    • Specific design criteria that will not be met;
    • Existing roadway characteristics;
    • Alternatives considered;
    • Comparison of the safety and operational performance of the roadway and other impacts such as right-of-way, community, environmental, cost, and access for  all modes of transportation;
    • Proposed mitigation measures; and
    • Compatibility with adjacent sections of roadway.

    Design Speed and Design Loading Structural Capacity are fundamental criteria in the design of a project and additional documentation is required for exceptions to these criteria.  Design speed exceptions should also describe the length of the proposed section with a lower design speed compared to the overall length of the project, and the measures that will be used in transitioning to adjacent sections with a different design speed.  Documentation for exceptions to the Design Loading Structural Capacity should include verification of safe load-carrying capacity (load rating) for all State unrestricted loads or routine permit loads and, in the case of bridges and tunnels on the Interstate System, all Federal legal loads.

  8. Are design exceptions approved on a project-by-project basis?

    Yes.  Design exceptions may be approved on a project-by-project basis. (23CFR625.3(f)).  Each design exception should be thoroughly evaluated to ensure the implications are understood and potential mitigation features considered before making any decisions when the design of a roadway feature falls outside of the established minimum values.  As a result, design exceptions cannot be approved for general application to an entire corridor or geographic region.

  9. At what point in the development of a project should design exceptions for a project on the NHS be reviewed and approved?

    Design exceptions may be approved at any time prior to finalizing the design of a project. However, agencies are encouraged to review and approve design exceptions as soon as sufficient analyses have been conducted and implication of these exceptions identified. The early consideration, evaluation, and decision on design exceptions will ensure more informed decision-making occurs early in the project development process, reducing the risk and cost of delays resulting from changes later in the process. Design exceptions are typically reviewed in conjunction with the overall review and approval of the plans, specifications, and estimates for a project on the NHS.

  10. What variances from NHS standards require FHWA review and approval of design exceptions?

    The FHWA requires the review and approval of design exceptions on high-speed (i.e., Interstate highways, other freeways, and roadways with design speed ≥ 50 mph) roadways on the NHS for 10 controlling criteria: design speed, lane width, shoulder width, horizontal curve radius, superelevation rate, maximum grade, stopping sight distance, cross slope, vertical clearance, and design loading structural capacity.  

    As of May 5, 2016, on low-speed roadways (i.e., non-freeways with design speed <50 mph) on the NHS, only the following two controlling criteria apply: design speed and design loading structural capacity.  While FHWA only requires the approval of design exceptions for these controlling criteria, agencies are encouraged to develop and implement procedures to analyze, evaluate, document, and approve all types of design variances. More information about this change can be found at http://www.fhwa.dot.gov/design/standards/160505.cfm.

  11. Who approves design exceptions for projects on the NHS?

    Design exceptions from NHS standards for the controlling criteria listed in Answer #10 must be approved by FHWA or on behalf of FHWA by a State DOT or local agency (as specified in 23CFR625.3(f)).

    On those projects where the State DOT has assumed FHWA's stewardship and oversight responsibilities (as specified in the State DOT-FHWA Stewardship Agreement), the State DOT must evaluate, approve, and document design exceptions as if they were approved by FHWA.

  12. Does a State DOT or local agency's approval of design exceptions on behalf of FHWA constitute a Federal Action?

    Yes.  The approval of design exception for any project on the NHS by FHWA is a Federal Action (that requires the evaluation and documentation of any environmental implications prior to taking any formal action or granting approval of these exceptions). The approval of design exceptions is a Federal Action regardless of the source of funding (e.g., Federal, State, local, private) or if a State DOT or local agency approves the design exceptions on behalf of FHWA. In other words, the Federal Action is the approval of the design exception and not the project. If a project on the NHS does not use Federal funding, the approval of design exceptions may be the only action or decision that may involve a State DOT or FHWA on these projects.  In many circumstances, the approval of the design exception will likely fall under categorical exclusion. (Reference 23CFR771.117(c). Also see question 13).

  13. Do design exceptions meet the criteria to be classified as a Categorical Exclusion (CE)?

    Typically, yes. The selection of the appropriate environmental review, documentation, and approval of FHWA's decision-making process will usually be based on the type and scope of the project. Design exceptions by themselves normally do not result in a change in the scope of a project or cause any significant impacts.  In many circumstances, the approval of the design exception will likely fall under categorical exclusion. (Reference 23CFR771.117(c)).  The FHWA Division Offices are encouraged to review and amend their programmatic CE agreements with their State DOTs to include design exceptions, as appropriate.

    Additional information and resources to support the environmental review, documentation, and approval that may be required on a project are available in FHWA's Environmental Review Toolkit.

  14. What information must State DOTs or local agencies review to determine if a proposed design exception can be classified as a CE?

    The review, consideration, and approval of design exceptions generally occurs after the impacts of a project's design have been reviewed and approved as complying with the applicable Federal and State or locally-required environmental finding, determination, or decision (as specified in  23CFR771 and any equivalent State or local requirements). A re-evaluation would be conducted to confirm that the applicable Federal and State or locally-required environmental finding, determination, or decision remained valid after the design exceptions were proposed.

    Typically design exceptions by themselves do not involve unusual circumstances or result in significant environmental impacts, making it highly unlikely that design exceptions alone would require an environmental review and documentation other than what is required for a CE action. For a project where the only Federal involvement is the approval of design exceptions, a CE would likely satisfy the NEPA evaluation and documentation requirements (as specified in 23CFR771).

    The FHWA Division Offices, State, or local agencies reviewing design exceptions also need to confirm proposed design exceptions are consistent with the project's previously completed environmental review and any commitments that were made, for the purpose of complying with applicable environmental requirements (as specified in 23CFR771 and any equivalent State or local requirements).

    The review and approval of design exceptions as a CE must be conducted in accordance with the State DOT-FHWA Stewardship and Oversight Agreement, any State DOT-FHWA CE Agreement, the State DOT's design policies, and FHWA approval standards. Based on past experience, the review of design exceptions must verify they do not involve significant environmental impacts or unusual circumstances (as specified in 23CFR771.117(a)and(b)). The documentation of this information may vary based on the procedures and practices of each agency (i.e., Design Study Reports and Project Fact Sheets).

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Updated: 10/12/2016
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