Manual Notice 2024-1
From:
Jason Pike, P.E.Manual:
Roadway Design Manual
Effective Date:
11/15/2024Purpose
The
Roadway Design Manual
has been revised, reorganized, and reformatted to update to the current national guidance, national standards, state-of-the-practice, recent transportation research, recent transportation policies, and new topics.Contents
A correspondence Table reflecting the reorganization of the Manual is below:
RDM (Update) | Current RDM (REV. 2) |
(Chapter) | (Chapter) |
Chapter 1 (General Guidance) | Chapter 1 (Design General) |
Chapter 2 (Performance Based Practical Design) - New Chapter/Topic | N/A |
Chapter 3 (Context and Facility Type Considerations) - New Chapter/Topic | N/A |
Chapter 4 (Basic Design Criteria) | Chapter 2 (Basic Design Criteria) |
Chapter 5 (Local Roadways 4R) | Chapter 3 (4R Design Criteria) |
Chapter 6 (Collectors 4R) | Chapter 3 (4R Design Criteria) |
Chapter 7 (Arterials 4R) | Chapter 3 (4R Design Criteria) |
Chapter 8 (Freeways 4R) | Chapter 3 (4R Design Criteria) |
Chapter 9 (Mobility Corridor Facilities 5R) | Chapter 8 (5R Design Criteria) |
Chapter 10 (3R Design Criteria) | Chapter 4 (3R Design Criteria) |
Chapter 11 (2R Design Criteria) | Chapter 5 (2R Design Criteria) |
Chapter 12 (Special Facilities) | Chapter 6 (Special Facilities) |
Chapter 13 (Intersections) | Chapter 2, Section 4 & 6, Chapter 3, & Appendix D (Right Turn Slip Lane Design Guidelines) |
Chapter 14 (Alternative Intersection and Interchange Design) | Appendix E (Alternative Intersections and Interchanges) |
Chapter 15 (Grade Separations and Interchanges) | Chapter 3 (4R Design Criteria) |
Chapter 16 (Driveways) | Appendix C (Driveway Design Guidelines) |
Chapter 17 (Roadside Safety Design and Roadside Safety Hardware) | Chapter 7, Section 1, and Appendix A (Longitudinal Barriers) |
Chapter 18 (Bicycle Facilities) | Chapter 6, Section 4 |
Chapter 19 (Pedestrian Facilities) | Chapter 7, Section 3 |
Chapter 20 (Motorcyclist Design Consideration) - New Chapter/Topic N/A | N/A |
Chapter 21 (Texas Highway Freight Network, Texas Trunk System, NHS, and STRAHNET) | Chapter 3 (4R Design Criteria) |
Chapter 22 (Transit Facilities) - New Chapter/Topic | N/A |
Chapter 23 (Temporary Traffic Control) - New Chapter/Topic | N/A |
Chapter 24 (Other Design Elements) | New Material + Chapter 7, Section 2 (Fencing) |
Chapter 25 (Index) | N/A |
Appendix A (Minimum Values for Design Exceptions) | Respective Minimum criteria values from applicable Chapters |
Appendix B (Minimum values for Design Waivers) | Respective Minimum criteria values from applicable Chapters |
Appendix C (List of References) | N/A |
Roadway Design Manual Format:
Chapter 1 (General Guidance)
describes the design elements that require Design Exceptions, Design Waivers, Design Variances, and the Texas Highway Freight Network’s Design Deviations. Also includes references for schematic design, access control, preliminary engineering, and maintenance in design. Chapter 2 (Performance Based Practical Design)
discusses the concepts and application of performance-based practical design. Also added guidance from recent research NCHRP 785 (Performance-Based Analysis of Geometric Design of Highways and Streets) and NCHRP 839 (A Performance-Based Highway Geometric Design Process). Chapter 3 (Context and Facility Type Considerations)
describes the five context classifications (urban, suburban, rural, rural town, & urban core) along with considerations for all modes of users and traffic networks. Context approach brought into alignment with AASHTO Greenbook and recent NCHRP research. Chapter 4 (Basic Design Criteria)
presents basic design criteria. Portions of this section will have application to all projects to varying degrees. The chapter discusses speed, terrain, traffic characteristics, sight distance, horizontal and vertical alignment, combination of horizontal & vertical alignment, cross-sectional elements, drainage facilities, older drivers & pedestrians, and roadway intersecting department projects. The dimensions given in this chapter will be referenced for most of the roadway classifications. Some notable updates include a superelevation table for the proper selection of superelevation methodology as a function of context and/or functional classification. Also, a discussion on the concept of Target Speed.Chapter 5 (Local Roadways 4R)
describes target design criteria (4R) for Local roads and streets (i.e., design speed, lane width, shoulder width, speed change lane width, median width, horizontal curve radius, superelevation rate, etc.) as a function of the Context. Chapter 6 (Collectors 4R)
describes target design criteria (4R) for Collector roads and streets (i.e., design speed, lane width, shoulder width, speed change lane width, median width, horizontal curve radius, superelevation rate, etc.) as a function of the Context. Chapter 7 (Arterials 4R)
describes target design criteria (4R) for Arterial roads and streets (i.e., design speed, lane width, shoulder width, speed change lane width, median width, horizontal curve radius, superelevation rate, etc.) as a function of the Context. Chapter 8 (Freeways 4R)
describes target design criteria (4R) for freeways (i.e., design speed, lane width, shoulder width, speed change lane width, median width, horizontal curve radius, superelevation rate, etc.). The Freeways chapter includes Interstates, Expressways, and Freeways as a function of the Context. Chapter 9 (Mobility Corridor Facilities 5R)
describes and provides design guidance on mobility corridors (5R) with design speeds of 85 mph to 100 mph (i.e., lane width & number, shoulders, cross slope, vertical clearance, stopping sight distance, grades, horizontal alignment, superelevation, vertical curves, roadside design criteria, ramps and direct connectors, etc.). Chapter 10 (3R Design Criteria)
describes rehabilitation (3R) project design criteria. Rehabilitation projects are intended to preserve and extend the service life of the existing roadway and to enhance safety. The chapter presents criteria for improvements and enhancements within the context of acceptable rehabilitation project design (including roadway tradeoff guidance and cross-section optimization, safety enhancements, frontage roads, bridges & bridge-class culverts, and Super 2 design). Also added guidance from recent research TTI 0- 6997 (Guidelines for Implementing Super 2 Corridors in Texas). Chapter 11 (2R Design Criteria)
describes non-freeway restoration (2R) project design criteria. Restoration projects are intended to restore the pavement structure, riding quality, or other necessary components to their existing cross section configuration. The chapter makes a special note that the addition of through travel lanes is not permitted under a restoration project. Chapter 12 (Special Facilities)
describes special facility design criteria. Special facilities may include off-system bridge projects, historical roadways or structures, and park roads. For these projects, the roadway may have preservation or economic considerations which have equal weight with the user access and mobility characteristics of the roadway, bridge, or other facility.Chapter 13 (Intersections)
discusses types of intersections and design criteria and considerations for the design of intersections as well as the design of right turn slip lanes. Chapter 14 (Alternative Intersection and Interchange Design)
provides guidance on alternative intersection designs. An overview, design considerations, pedestrian and bicyclist considerations, and access management are discussed for Roundabouts, Diverging Diamond Interchanges (DDI), Median U-Turn Intersections (MUT), Restricted Crossing U-Turn Intersections (RCUT), Displaced Left Turn Intersections (DLT), and Continuous Green T-Intersection (CGT). Chapter 15 (Grade Separations and Interchanges)
discusses grade separations and interchanges. Describes design criteria for ramps and direct connectors. Added guidance from recent research RTI 0-7047 (Establish Guidelines for Designing Auxiliary Lanes on Frontage Roads). The guidance from RTI 0-7047 provides guidance on merge auxiliary lanes, weaving auxiliary lanes, distance recommendations from an exit ramp to the downstream intersection, left-turn deceleration lanes, right-turn deceleration lanes, and U-turn/turnaround deceleration lanes. Also added guidance from recent research NCHRP 15-56 (Selecting Ramp Design Speeds Vol. 1 & 2). Chapter 16 (Driveways)
discusses design criteria and considerations for the design of driveways. Chapter 17 (Roadside Safety Design and Roadside Safety Hardware)
discusses the design of roadside safety and roadside safety hardware. Topics include general applications of conditions for roadside barriers, types of roadside barriers (Rigid, Semi-rigid, flexible), metal beam guard fence guidance, length of need methodology, Median barrier, crash cushion attenuators, and emergency turnarounds. Chapter 18 (Bicycle Facilities)
describes design criteria and considerations for the design of bicycle facilities. Chapter 19 (Pedestrian Facilities)
describes design criteria and considerations for the design of pedestrian facilities. This includes updates due to the recently adopted PROWAG criteria. Chapter 20 (Motorcyclist Design Consideration)
discusses motorcyclist design considerations such as pavement features, roadside features, highway features, and motorcycle safety during construction. Chapter 21 (Texas Highway Freight Network, Texas Trunk System, NHS, and STRAHNET)
describes the policy for highways on the Texas Highway Freight Network, Texas Trunk System, NHS, and STRAHNET. Chapter 22 (Transit Facilities)
discusses the design of transit facilities for buses and trains as it pertains to vehicular roadways such as Right of Way requirements (i.e., passenger platforms, intersections, transit centers, and dedicated transitways) and Roadway Design (i.e., lane widths, profiles, vertical clearances, acceleration/deceleration, and transit stops).Chapter 23 (Temporary Traffic Control)
discusses design criteria and considerations for the design of temporary traffic control (TTC) (i.e., purpose of TTC design, safety in TTC design, federal regulations, duration, typical sections, shoulder widths, lane widths, bike & ped requirements, property access requirements, temporary geometry, and example problems). Chapter 24 (Other Design Elements)
discusses roadway design considerations for fencing, illumination, signing, pavement marking, intelligent transportation systems (ITS), and wildlife crossings. Appendix A
contains tables of the minimum design values, that if not met, would require a design exception as described in Chapter 1. Appendix B
contains tables of the minimum design values, that if not met, would require a design waiver as described in Chapter 1. Appendix C
contains the source references.Significant Updates to the RDM:
- Performance Based Practical Design
- Context Classification
- Speed (Design, Operating, Posted, & Target): a newer emphasis on Target Speed that is the operating speed that the designer intends for drivers to use. In mixed-use urban areas, the target speed is the highest speed at which vehicles should operate on a low-speed thoroughfare in a specific context, consistent with the level of multimodal activity generated by adjacent land uses, to provide both mobility for motor vehicles and a desirable environment for pedestrians, bicyclists, and public transit users. In general, the Target speed for rural roadways should be on the higher end of the design speed range.
- Target Design Criteria (4R) Local Roads (Ch. 5), Collector Roads (Ch. 6), Arterials (Ch. 7), and Freeways (Ch. 8): Changing to an emphasis on Target values (with the minimum values provided in the Appendices). The Tables now more align with the AASHTO Greenbook, 4R Chapters are categorized by functional classifications and within the Chapters they are delineated by Context (Rural, Rural Town, Suburban, Urban, & Urban Core) for the respective Design Elements (i.e., design speed, travel lane width, shoulder width, median width, etc.), and typical Sections (e.g., urban core typical section).
- 3R Design Criteria (Including Freeways & Interstates and Roadway Tradeoff Guidance & Cross-Section Optimization): In 2022 FHWA issued a final rule which will allow State departments of transportation (State DOT) to adopt procedures or design criteria, as approved by FHWA, that enable the State to undertake 3R projects on Freeways, including Interstate highways, without utilizing design exceptions as long as the 3R procedures or criteria are met. The practice of roadway design is changing to a more performance-based (PBPD), flexible approach, particularly for 3R projects. Rather than focusing on meeting minimal dimensional criteria, 3R projects can be developed based on project-specific conditions and existing and expected future roadway performance. NCHRP 876 in particular presents a rational approach for estimating the cost-effectiveness of including safety and operational improvements in a 3R project. This PBPD approach provides the basis for determining design improvements that should be incorporated into 3R projects. NCHRP 15-50 (companion to NCHRP 876) reviewed the latest safety literature and developed cost-benefit analysis equations for the most common design improvements applied to 3R projects (including spreadsheet tools Tool 1 and Tool 2).Roadway Tradeoff Guidance and Cross-Section Optimization: TTI research report 0- 7035-R1 studied the safety and operational benefits of converting four-lane undivided highways into other cross section alternatives without changing the overall pavement width, or slightly increasing the overall width dependent on available ROW and clear zone needs. The researchers developed a framework based on safety and operational effects that allows the design engineer to select a cross section depending on traffic volume, heavy vehicle mix, existing cross-sectional width, and access-point density. Also added guidance from follow up recent research TTI 0-7136 (Texas Guidelines for Optimizing Roadway Cross-Section).
- Intersections: includes design considerations (i.e., intersection characteristics, functional area, design objectives, user groups, and capacity), types of intersections (i.e., three-leg and four-leg), alignment and profile, intersection sight distance (i.e., case A, B, C, D, E, F, and G), turning roadways, speed change lanes, median openings, right turn slip lanes, minimum turning radii, and railroad highway grade crossings.
- Alternative Intersection and Interchange Design (additional design guidance). Also added recent research from RTI 0-7036 (Roundabouts/Innovative Intersections), NCHRP Synthesis 550 (Alternative Intersection Design and Selection), and NCHRP 948 (Guide for Ped and Bike Safety at Alternative and Other Intersections and Interchanges), and NCHRP 1043 (Guide for Roundabouts) to RDM chapter 14.
- Grade Separations and Interchanges
- Bicycle Facilities (Micromobility): includes a variety of electrical powered micromobility and power-driven mobility devices (i.e., human or electric powered transportation device, including bicycles, scooters, electric assist bicycles, electric scooters and other small, lightweight, wheeled conveyances) that may be operated on a street, sidewalk, or bikeway unless restricted by a jurisdiction. Micromobility limited to top speeds of 30 mph or less and complements transit by providing first/last mile transportation.
- Pedestrian Facilities (PROWAG): On August 8, 2023, the US Access Board published PROWAG to provide guidance. PROWAG provides a useful framework to meet TxDOT’s obligations to make our programs, services, and activities in the public right-of-way readily accessible and useable by all individuals including those with disabilities. The Pedestrian Facilities chapter has been updated to the August 8, 2023 edition of PROWAG.
- Motorcyclist Design Considerations
- Temporary Traffic Control
- THFN, Texas Trunk System, NHS, and STRHNET
- Transit Facilities
Instructions
This manual, and all revisions, applies to all transportation project development (all modes), whether developed by the department or by other entities. Due to projects that may be further along in development with current criteria, this manual, and all revisions, will be effective for all projects beginning with March 2026 Letting, and if final Schematic or 30% plans have not been approved by May 31, 2025. The Districts have the option to use these revisions prior to these dates.
Contact
Kenneth Mora, P.E., Roadway Standards and Research Lead Design Division (PDS),
, (512) 416-2678
Archives
Past manual notices are available in a
.