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Section 2: Design Exceptions, Design Waivers and Design Variances

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Overview

This subsection discusses the following topics:

  • design exceptions
  • design waivers
  • design variances
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Design Exceptions

A design exception is required whenever the criteria for certain 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. The determination of whether a design exception exists rests with the district, unless the project is subject to federal oversight or review. A design exception is not required when values exceed the guidelines for the controlling criteria.

Design exceptions for plans, specifications and estimates, designated federal oversight under the current Federal Oversight Agreement must be reviewed and approved by the FHWA. Design exceptions for all schematics on the NHS with the exception of preventive maintenance, freeway safety and 3R type projects must be reviewed and approved by the FHWA.

Design exceptions for all projects on the interstate system must also be reviewed and approved by the FHWA.

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

Final approval of a roadway design exception must be signed by the district engineer and this signature authority cannot be delegated. 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:

  • Director of Transportation Planning and Development,
  • Director of Construction,
  • Director of Operations/Traffic, and
  • Area Engineer (not responsible for project management).

The reviews of any three of the four member committee would constitute a quorum for recommending signature action.

The complete documentation for a roadway exception should be retained permanently in the district project files and a copy furnished to the Design Division. 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 that will require a design exception.

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

  • Deficient Bridge Rails (high volume roadways)
  • Design Speed (high volume roadways)
  • Horizontal Alignment (high volume roadways)
  • Vertical Alignment (high volume roadways)
  • Superelevation (high volume roadways)
  • Grades (high volume roadways)
  • Lane Width
  • Shoulder Width
  • Bridge Width (see Bridge Project Development Manual)
  • Structural Capacity (see Bridge Project Development Manual)

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.

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:

  • Design Speed
  • Lane Width
  • Shoulder Width
  • Structural Capacity (see Bridge Project Development Manual)
  • Horizontal Alignment
  • Vertical Alignment
  • Grades
  • Cross Slope
  • Superelevation
  • Minimum Structure Width, Face to Face of Rail: 24 ft [7.2 m].

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

  • Roadway Width
  • Load Carrying Capacity (Operating Rating)

Park Road Projects. Design exceptions are not applicable to park road projects that are off the state highway system. 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 must meet the required design criteria for the appropriate roadway classification including exception or waiver requirements.

Bicycle Facilities. Design exceptions are necessary when the minimum requirements given in the AASHTO Guide for the Development of Bicycle Facilities for on-street bicycle lanes and increased shared lane width cannot be met.

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Design Waivers

When the criteria is not met in a noncontrolling category, a design exception is not required. However, variations from the criteria in these cases 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 files and a copy furnished to the Design Division.

The following project categories will have noncontrolling criteria that dictate a design waiver.

New Location and Reconstruction Projects (4R). The list below gives the noncontrolling criteria that will require a design waiver:

  • Curb Parking Lane Width
  • Speed Change (refuge) Lane Width
  • Length of Speed Change Lanes
  • Curb Offset
  • Median Opening Width
  • Horizontal Clearance (clear zone)
  • Railroad Overpass Geometrics
  • Guardrail Length (unless for access accommodation; see Appendix A, Metal Beam Guardrails).

    Resurfacing, Restoration or Rehabilitation (3R) Projects. The list below gives the noncontrolling criteria that will require a design waiver. For 3R projects, low volume roadways are defined as current ADT of less than 1500.

  • Design Speed (low volume roadways)
  • Horizontal Alignment (low volume roadways)
  • Vertical Alignment (low volume roadways)
  • Superelevation (low volume roadways)
  • Grades (low volume roadways)
  • Deficient Bridge Rails (low volume roadways)
  • Obstruction Clearance (clear zone)
  • Turn Lane Width
  • Length of Speed Change Lanes
  • Parallel Parking Lane Width
  • Guardrail Length (unless for access accommodation; see Appendix A, Metal Beam Guardrails).

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

Special Facilities. Design waivers are not applicable to special facility projects including (1) off-system bridge replacement and rehabilitation projects, (2) off-system historically significant bridge projects, or (3) park road projects.

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

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Design Variances

A design variance is required whenever the design guidelines specified in the Americans with Disabilities Act Accessibility Guidelines (ADAAG) and the Texas Accessibility Standards are not met. Design variances should be sent to the Design Division for forwarding to the Texas Department of Licensing and Regulation for approval. Refer to Sidewalks and Pedestrian Elements in Chapter 2 for additional discussion.

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