Chapter 10: 3R Design Criteria
10.1 Design Considerations
10.1.1 Introduction
Rehabilitation (3R) projects consist of transportation projects that extend the service life and enhance the safety of a roadway. In addition to resurfacing and restoration, the activities may include upgrading the geometric design and safety of the facility. Work on 3R projects does not include the addition of through travel lanes (i.e., no added capacity). 3R projects may include upgrading geometric features such as roadway widening, minor horizontal realignment, and bridge improvements to meet current standards for structural loading and accommodate the approach roadway width. See
for additional clarification on horizontal and vertical alignment.
Design guidelines for 3R projects have been developed to allow for greater design flexibility.
At the District’s option, design values above those presented in this chapter may be used.
3R design decisions should be based on an assessment of the safety and traffic operational performance of the existing road and the cost-effectiveness of potential design improvements. Geometric design improvements should be considered as part of a 3R project in the following situations:
- An analysis of the crash history of the existing road identifies one or more crash patterns that are potentially correctable by a specific design improvement;
- An analysis of the traffic operational level of service (LOS) indicates that the LOS is currently lower than the target LOS for the facility or will become lower than the target LOS within the service life of the planned pavement resurfacing (typically 7 to 12 years); or
- A design improvement would reduce sufficient crashes over its service life to be cost effective (i.e., the anticipated crash reduction benefits over the service life of the project exceed the improvement implementation cost).
With a few exceptions (e.g., see bicycle accommodations below), in the absence of any of the three situations defined above, there is no indication that a design improvement is needed as part of a 3R project, and the existing roadway and roadside geometric features should remain in place. Design or traffic control improvements, in addition to pavement resurfacing, should be considered where anticipated benefits exceed anticipated costs.
For Benefit cost evaluations for 3R projects, spreadsheet tools and methods such as those identified in the
, or Tools 1 and 2 from
may be used to assess both single design alternatives and comparing several alternatives or combinations of alternatives. These tools generate both a Benefit/Cost (B/C) ratio (including safety benefits) as well as the net present value of benefits. Generally, B/C ratios of 2.0 or higher would represent a significant benefit; B/C ratios of between 2.0 and 1.0 although considered positive; additional sensitivity analyses should be done to determine whether or not the identified upgrades are sufficiently beneficial for the project and TxDOT. B/C values below 1.0 should generally not be considered.
These analyses would serve as the basis for determining whether or not specific upgrades should be made. These analyses would also serve as the basis in the justification for any needed design exceptions or design waivers (if established minimums are not met or not intended to be met) if the Benefit cost analysis indicates that such an improvement to the respective minimum values is not warranted.
These guidelines offer sufficient flexibility to allow cost-effective design and further compliance with the program goals of preserving and extending the service life and enhancing safety. While highway safety may not be the primary reason for initiating a 3R project, it is an essential element of all projects. 3R projects should identify and incorporate appropriate safety enhancements.
For 3R projects, current average daily traffic (ADT) volumes of less than 1,500 are defined as low traffic volume roadways.
3R Projects must be assessed to determine if bicycle accommodations are required per Chapter 18
If bicycle facilities are provided, see
for requirements.
10.1.2 Freeways and Interstates
In 2022 FHWA issued a final rule, which will allow State DOTs to adopt procedures or design criteria, as approved by FHWA, that enable the State to undertake resurfacing, restoration, and rehabilitation (RRR) projects on freeways, including Interstate highways. Freeway facilities follow the same 3R principles and analyses in this chapter. However, a design exception or design waiver would be needed if the respective 4R freeway minimum criteria (as specified in App. A, or App. B) are not met or not intended to be met. A benefit-cost evaluation would again serve as the basis for any needed design exceptions or design waivers.
10.1.3 Pavement Design
Pavement rehabilitation includes all pavement-related work undertaken to extend the service life of an existing facility. This includes placement of additional surfacing material and/or other work necessary to return an existing roadway, including shoulders, to a condition of structural and/or functional adequacy. The following are some examples of pavement rehabilitation work:
- Resurfacing to provide improved structural capacity and/or serviceability;
- Removing and replacing deteriorated materials;
- Replacing or restoring malfunctioning joints;
- Reworking or strengthening of bases and subbases;
- Recycling existing materials; and
- Adding underdrains.
The existing pavement condition and deficiencies should be identified for 3R projects. Design strategies selected to correct deficiencies will vary from seal coats to overlays to complete pavement structure reconstruction. Projects that consist only of seal coats or overlays, and do not meet the design guidelines presented in this chapter, are not eligible for rehabilitation funding
Reference TxDOT’s
for additional information related to pavement rehabilitation.
10.1.4 Minimum Geometric Design Values
Minimum 3R geometric design guidelines for roadways and frontage roads are provided in Appendix A and Appendix B.
A
design exception
is required for not meeting the minimum values shown in Appendix A tables. A design waiver
is required for not meeting the minimum values shown in Appendix B tables. See
with respect to vertical and horizontal alignment. Criteria is designated as applicable to high-volume roadways, low-volume roadways, or both. A Benefit cost evaluation should serve as the basis for design exceptions and design waivers
(see
).10.1.5 Design Values
Where existing highway features comply with the minimum design values given in the respective Appendices, the designer may choose not to modify these features. However, where existing features do not meet these values, the designer may upgrade to the design values shown in this manual following a performance-based approach that uses benefit-cost analysis in design decisions.
These values are intended for use on typical rehabilitation projects. The designer may select higher values to be consistent with adjoining roadway sections, to provide consistency with prevailing conditions on similar roadways in the area, or to provide operational improvements at specific locations.
10.1.5.1 Alignment
Typically, 3R projects will involve minor or no change in vertical or horizontal alignment. However, consider flattening curves or other improvements where a crash history indicates a concern or where existing curvature is inconsistent with prevailing conditions within the project or on similar roadways in the area. Where appropriate, consider superelevation improvements as well. Where the superelevation of an existing curve is less than the design superelevation value of the roadway by more than 1%, the superelevation should be restored. These types of isolated improvements are not considered substantial and thus may be included for consideration in 3R projects.
Substantial changes in existing horizontal and/or vertical alignment improvements are considered reconstruction.
Projects with substantial changes in existing alignment should be developed to reconstruction (4R) standards.
Design exceptions or design waivers for vertical or horizontal alignment on a 3R project will only be required when crash history or prevailing conditions indicate needed upgrades, but those upgrades are not included in the 3R project.
10.1.5.2 Design Speed
Reconstruction of horizontal and vertical alignments should be considered when the design speed of the roadway in question is not consistent with the existing geometrics.
For roadways that do not meet the minimum 3R design speeds (see
or
for Freeways), an evaluation should be done to examine high-frequency crash locations (and potential crash locations) to determine whether cost-effective alignment revisions can be accomplished with the resources available. These projects should be designed to accommodate the anticipated operating speed where practicable. When the anticipated operating speed cannot be met, additional traffic safety measures should be provided including, but not limited to, enhanced signage, pavement markings and delineation.
10.1.5.3 Side and Backslopes
Roadside flattening should be considered for each 3R project with roadside slopes steeper than 1V:4H where sufficient ROW is available. A benefit cost analysis should be conducted to determine the net benefit and viability of such an upgrade (see
).
10.1.5.4 Lane and Shoulder Widths
Consideration should be given to increasing lane widths to 12-ft in conjunction with rehabilitation projects where the highway is a high-volume route utilized extensively by large trucks. Widening shoulders has generally been shown to have a greater reduction in crashes versus widening travel lanes. Factor in this consideration along with other considerations that determine the scope of a project, including expected service life of the proposed rehabilitation work, long-range plans for the route, and design standards of nearby segments on the route. A benefit cost analysis should be conducted to determine the net benefit and viability of such an upgrade.
10.1.5.5 Bridge Widths
Roadway widths on bridges with curbs are measured to the face of curb. Roadway widths on bridges without curbs are measured to the nominal face of rail.
Refer to TxDOT’s
and TxDOT
for the nominal widths of specific rail types and additional guidance.