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.

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.

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.

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 ).

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.

Refer to TxDOT’s and TxDOT for the nominal widths of specific rail types and additional guidance.