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Section 2: Design Exceptions, Design Waivers, Design Variances, and Texas Highway Freight Network (THFN) Design Deviations

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Overview

This subsection discusses the following topics:

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Design Exceptions

A design exception is required whenever the controlling criteria specified for the different categories of construction projects (i.e., 4R, 3R, 2R, Special Facilities, Off-System Historically Significant Bridge Projects, Park Road Projects, and on-street Bicycle Facilities) are not met. Approval of a design exception rests with the TxDOT District, unless the project is subject to federal oversight or review. A design exception is not required when values exceed the minimum guidelines for the controlling criteria.

As per the “Stewardship and Oversight Agreement on Project Assumption and Program Oversight By and Between Federal Highway Administration, Texas Division and the State of Texas Department of Transportation, 2015” (FHWA-TxDOT S&O Agreement, 2015), the FHWA is required to approve any design exceptions on an Interstate. Additionally, if a project (Interstate or other) is identified on the FHWA Texas Division's list of “Projects of Division Interest” (PoDI), and the project’s PoDI plan identifies any design exception responsibility to FHWA, then all proposed design exceptions for that project will be required to be submitted to FHWA. All other project design exceptions are to be approved by the TxDOT District. Design exceptions to be submitted to the FHWA, must first be submitted to the Design Division - Project Development Support Section for review; the Design Division - Project Development Support Section will then transmit the design exception to the FHWA for approval.

Design exceptions involving the design loading structural capacity or bridge rails shall be sent to the Bridge Division for their review and approval.

All design exceptions must be signed by the TxDOT District Engineer and this signature authority cannot be delegated. Design exceptions must be documented on the Form 1002.

For flexibility and efficiency in meeting project design schedules, the review of design exceptions and recommendations for approval/non-approval may be established individually by each district. For example, a four person review committee might be established which includes:

The approval/non-approval of the majority of the committee members would constitute a quorum for recommending signature action.

The complete documentation for a roadway design exception should be retained permanently in the district project files. Since the construction plans are sealed, the design exception documentation does not require an engineer’s seal.

The following project categories will have controlling criteria that dictate a design exception.

New Location and Reconstruction Projects (4R). The list below gives the controlling criteria for 4R projects that will require a design exception.

NOTE: SSD applies to horizontal alignments, and crest vertical curves for the purposes of a Design Exception. SSD for crest vertical curves is a direct correlation with the K-Value. If the minimum K-Value is satisfied for a crest vertical curve (Fig. 2-5), then the vertical SSD is satisfied under usual conditions.

Resurfacing, Restoration or Rehabilitation (3R) Projects. The list below gives the controlling criteria for 3R projects that will require a design exception. For 3R projects, high volume roadways are defined as current ADT of 1500 and greater.

NOTE: SSD only applies to crest vertical curves for the purposes of a Design Exception for 3R high-volume roadways. SSD for crest vertical curves is a direct correlation with the K-Value. If the minimum K-Value is satisfied for a crest vertical curve (Fig. 2-5), then the vertical SSD is satisfied under usual conditions.

Resurfacing or Restoration Projects (2R). Design exceptions are required for 2R projects any time the existing geometric or bridge features for the proposed project will be reduced.

Bicycle Facilities. If the minimum requirements given in the AASHTO Guide for the Development of Bicycle Facilities for bicycle lanes or shared lanes cannot be met, a design exception will need to be submitted. See Chapter 6, Section 4 for additional information.

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  • For new shared lanes, the minimum lane width shall be 14 ft [4.2 m]. Widths less than this will require a design exception.
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  • For new bicycle lanes, the minimum clear width shall be 4 ft [1.2 m] measured to the longitudinal joint. Widths less than this will require a design exception.
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  • If the minimum requirements given in the AASHTO Guide for the Development of Bicycle Facilities for shared use paths cannot be met, a design waiver will be necessary per the following Design Waiver section.

Special Facilities. For off-system bridge replacement and rehabilitation projects with current ADT of 400 or less, the following design elements must meet or improve conditions that are typical on the remainder of the roadway or a design exception will be necessary:

Off-System Historically Significant Bridge Projects. The list below gives the controlling criteria that will require a design exception.

Park Road Projects. Design exceptions are not applicable to park road projects that are off the state highway system, designated as Park and Wildlife Roads (PW). Design is based on the criteria and guidance given in the current publication of the Texas Parks and Wildlife Department Design Standards for Roads and Parking, or as approved by the Texas Parks and Wildlife Department.

On-system park road projects, designated as Park Roads (PR) must meet the required design criteria for the appropriate roadway classification including design exception or design waiver requirements.

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Design Waivers

When the criterion is not met in a non-controlling category, a design exception is not required. However, a departure from the minimum criteria will be handled by design waivers at the district level. Design waivers will be granted as the district authorizes. The complete documentation should be retained permanently in the district project.

The non-controlling criteria for the following project categories will require a design waiver.

New Location and Reconstruction Projects (4R).

NOTE: Sag Vertical Curve Length applies to sag vertical curves for the purposes of a 4R Design Waiver. Sag Vertical Curve Length for vertical alignment is a direct correlation with the K-Value. If the minimum K-Value is satisfied for a sag vertical curve (Fig. 2-6), then the Sag Vertical Curve Length is satisfied under usual conditions. For minimum Sag Vertical Curve Lengths at Under-Crossings see Fig. 2-1A.

Resurfacing, Restoration or Rehabilitation (3R) Projects. For 3R projects, low volume roadways are defined as a current ADT of less than 1500.

NOTE: SSD applies only to crest vertical curves for the purposes of a Design Waiver for 3R low-volume roadways. SSD for crest vertical curves is a direct correlation with the K-Value. If the minimum K-Value is satisfied for a crest vertical curve (Fig. 2-5), then the vertical SSD is satisfied under usual conditions.

Sag Vertical Curve Length applies to sag vertical curves for the purposes of a 3R Design Waiver. Sag Vertical Curve Length for vertical alignment is a direct correlation with the K-Value. If the minimum K-Value is satisfied for a sag vertical curve (Fig. 2-6), then the Sag Vertical Curve Length is satisfied under usual conditions. For minimum Sag Vertical Curve Lengths at Under-Crossings see Fig. 2-1A.

Resurfacing or Restoration Projects (2R). Design waivers are not applicable to 2R projects.

Special Facilities. For off-system bridge replacement and rehabilitation projects:

NOTE: Sag Vertical Curve Length applies to sag vertical curves for the purposes of a Design Waiver. Sag Vertical Curve Length for vertical alignment is a direct correlation with the K-Value. If the minimum K-Value is satisfied for a sag vertical curve (Fig. 2-6), then the Sag Vertical Curve Length is satisfied under usual conditions.

Design waivers are also necessary when the minimum requirements given in the AASHTO Guide for the Development of Bicycle Facilities for shared use paths cannot be met.

Design waivers are not applicable to off-system historically significant bridge projects or off-system park road projects.

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Design Variances

A design variance is required whenever the design guidelines specified in the Texas Accessibility Standards (TAS) are not met. Design variances shall be sent to Texas Department of Licensing and Regulation (TDLR) for approval. Refer to Sidewalks and Pedestrian Elements in Chapter 2 for additional discussion. Design variance documentation should also be developed when the Proposed Accessibility Guidelines for Pedestrian Facilities in the Public Right of Way (PROWAG) cannot be met. This documentation should be kept in the project files.

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Texas Highway Freight Network (THFN) Design Deviations

A Texas Highway Freight Network (THFN) Design Deviation will be required for projects Letting September 1, 2020 or later that do not meet specified Bridge Vertical Clearance Requirements. Chapter 3, Section 8 contains the specific requirements for the THFN. The Deviation request is exclusive of (and in addition to) the Design Exception that may be needed for Vertical Clearances not meeting the specified requirements in Chapter 3 of the respective roadway facility. The THFN Deviation requests will be submitted to the Design Division – Project Development Support Section, and will be reviewed by an assigned Design Deviation Committee.

A Deviation request form, process flowchart, and other information can be found on the Design Division – Roadway and Hydraulics Design website.

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