Section 2: Design Exceptions, Design Waivers and Design Variances
Anchor: #i1002889Overview
This subsection discusses the following topics:
- design exceptions
- design waivers
- design variances
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, or Special Facilities) are not met. The procedures for handling design exception requests are outlined in the Project Development Policy Manual, Appendix C, Section 5, Roadway Design Exception Process. A design exception is not required when values exceed the guidelines for the controlling criteria.
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.
- Design Speed
- Lane Width
- Shoulder Width
- Bridge Width (see Bridge Project Development Manual)
- Structural Capacity (see Bridge Project Development Manual)
- Horizontal Alignment
- Vertical Alignment
- Grades
- Stopping Sight Distance
- Cross Slope
- Superelevation
- Vertical Clearance
Resurfacing, Restoration or Rehabilitation (3R) Projects. The list below gives the controlling criteria that will require a design exception.
- 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 bicycle lanes cannot be met.
Anchor: #i1003162Design 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, or the documentation may be forwarded to the Design Division for retention.
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:
- 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.
Anchor: #i1003307Design 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.