Hermanus Steyn and Julia Knudsen 0 0 MONTANA DEPARTMENT OF TRANSPORTATION (MDT) ROAD DESIGN MANUAL (RDM) UPDATE: INCORPORATING PERFORMANCE BASED DESIGN Submission Date: November, Corresponding Author: Hermanus J. Steyn, Pr. Eng., P.E. Principal Engineer Kittelson & Associates, Inc. 0 SW Alder St., Suite 00 Portland, Oregon Phone: (0) - Fax: (0) - E-mail: hsteyn@kittelson.com Additional Author: Julia Knudsen, P.E. Senior Engineer Kittelson & Associates, Inc. 0 SW Alder St., Suite 00 Portland, Oregon Phone: (0) - Fax: (0) - E-mail: jknudsen@kittelson.com Word Count: abstract () + text (,0) + figure (00) + references (0) =,00 Figures, Tables, or Photographs:
Hermanus Steyn and Julia Knudsen 0 ABSTRACT: Montana Department of Transportation (MDT) is updating their Road Design Manual (RDM). The project includes two phases, Phase I: Develop Annotated Outline for New Road Design Manual and Phase II: Develop New Road Design Manual. As part of Phase I, the project team developed a table of contents for the new RDM; developed white papers on key road design topics for consideration in the new RDM; developed an annotated outline for the new RDM; and prepared a sample draft chapter. The team (consultant and MDT staff) gathered input and worked collaboratively to generate design material that reflects current design research, updated project development processes, and best practices for road design (i.e., performance based design). During Phase II, the team used the annotated outline to develop the new RDM. The team grouped the new/reorganized chapters and supporting material of the RDM into bundles to provide smaller, more reasonable deliverables for review. This approach spread the deliverables over several months rather than one large deliverable (entire manual) towards the end of the project. With this approach, consultant and MDT staff could stagger preparation and review timeframes to be efficient throughout the project duration. The new MDT RDM incorporates a performance-based road design approach into the road design project development process that enables designers to make informed decisions about the performance tradeoffs, which is referenced throughout the manual. In addition, the manual update approach provides a strategy for others to potentially update their design manuals.
Hermanus Steyn and Julia Knudsen 0 0 0 INTRODUCTION The existing Montana Department of Transportation (MDT) Road Design Manual (RDM) was previously updated in the 0 s. Since that time, MDT has prepared numerous design memoranda to reflect new design methodologies and standards. MDT appointed Kittelson & Associates, Inc. (KAI) to update the RDM to reflect the latest national design methodologies, guidelines, and standards. In addition, the updated manual will be presented in an updated format with links to other references and material to provide designers with a user-friendly resource for their projects (). An important element of developing the manual is understanding MDT s structure and the interaction between respective departments. The overall goals were to take a fresh look at roadway design from a national perspective, streamline the design approach, as well as minimize repetitiveness, especially between departments within MDT. Finally, the objective was to effectively communicate engineering principles and remind engineers that design is more than just applying a standard from a table, but rather understanding the tradeoffs and how design, safety and operations interact during the design of a project. APPROACH FOR UPDATING THE RDM The project team (KAI and MDT staff) developed a two-phase approach to provide an opportunity for the team to take a fresh look at the RDM, not spending excessive time early in the project, but developing an outline prior to delving into the material development. Phase I Establishing Annotated Outline Based on brainstorming sessions, the project team outlined the following Phase I tasks: Establish a table of contents; Develop white papers on key road design topics for consideration; Develop an annotated outline; and Prepare a sample chapter illustrating the format of chapters, text style, exhibits (e.g., figures, tables), headers, footers, and margins. Author Notes located in the margin of the page are introduced which allow an opportunity for key considerations to be emphasized and additional references added. After MDT accepted the Phase I deliverables, the project team proceeded with Phase II. Phase II Developing New Road Design Manual The project team used the annotated outline as the framework to develop the RDM. We grouped the new/reorganized chapters and supporting material of the RDM into six () bundles to provide smaller, more reasonable deliverables (volume/size) to MDT for review. This approach spreads the deliverables over several months rather than one large deliverable (entire manual) towards the end of the project. With this approach, KAI and MDT staff can stagger preparation and review timeframes to be efficient throughout the project duration. In addition, the objective is to accept each chapter as a final Draft deliverable, with only minor modifications when the chapters are combined into the final Draft RDM manual. INCORPORATING PERFORMANCE-BASED DESIGN IN THE RDM Incorporating a performance-based road design approach into the road design project development process enables designers to make informed decisions about the performance tradeoffs. This is especially helpful when developing solutions in fiscally and physically
Hermanus Steyn and Julia Knudsen 0 constrained environments. National activities and publications, such as Federal Highway Administration s (FHWA) Performance-Based Practical Design initiatives and National Cooperative Highway Research Program (NCHRP) Report, Performance-Based Analysis of Geometric Design of Highways and Streets, have resulted in a framework for how this approach can be executed within a design project (). While design teams may have been using similar practical design approaches in the past, clear documentation of a performance-based approach can encourage effective problem-solving, collaborative decision-making, and an overall greater return on infrastructure investments. A fundamental model for this approach documented in NCHRP Report is shown in Figure. FIGURE - Fundamental Model for Performance-Based Analysis for Geometric Design of Highways and Streets (Source: NCHRP Report ). Figure illustrates the following basic steps in performance-based analysis to inform geometric design. Each step of this approach is further described below ().. Identify intended outcomes (desired project performance) and project purpose and need. This may include any number of project context-driven categories helping to identify project objectives. Identifying project purpose and need early in the project development process, such as the planning stage, can help guide the project team as decisions are made in the subsequent stages of the project.. Establish geometric design decisions. This could include establishing design criteria and developing preliminary designs. A preliminary review of potential design exceptions required for the project may be identified at this stage. Documenting design decisions and the considerations supporting those choices that result in flexible design solutions is a key component in managing project risk.
Hermanus Steyn and Julia Knudsen 0 0 0. Evaluate performance outcomes. This is the point at which the performance outcomes of the geometric design choices are evaluated. Establishing the geometric performance allows an assessment of the effectiveness of the design decision in relation to the project purpose.. Refine decisions based on performance. Depending on the results of the evaluation of the design performance, there can be an iterative process to refine design decisions to bring resulting performance in line with project purpose. This type of approach can be used as a problem-solving tool throughout a project and a framework for maintaining a consistent project scope throughout each stage of the process.. Assess financial feasibility. In this step, the benefits associated with design choices are assessed to establish the monetary value of the geometric solution compared to the intended project outcomes. Cost estimates and project funding information will be used at this stage to help make project decisions.. Select project(s) or alternatives. As project alternatives are deemed viable within the project context, they may be advanced for more detailed evaluations and/or environmental reviews. At this stage of the project, a selected alternative may be carried forward to a final design stage where additional road design details are reviewed and design plans are prepared. The fundamental model provides a decision making approach that can help the design team to develop and evaluate design choices within each unique contextual design environment. The focus is on performance improvements that benefit the project and system needs and allows decisions to be made based on performance analysis. Executing this approach involves using relevant, objective data to support the design decisions and developing an analytical approach tailored to the project purpose and need. This will require an awareness of the resources available to quantify specific performance measures or qualitatively describe the anticipated effect of a given roadway, intersection, or interchange design. Examples of performance-based tools that can be used as a resource for conducting a project with this approach are described below: American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual (HSM) provides factual information and proven analysis tools for crash frequency prediction (). The HSM helps users integrate quantitative crash frequency and severity performance measures into roadway planning, design, operations, and maintenance decisions. HSM analytical tools allow users to assess the safety impacts of transportation project and program decisions (). The HSM predictive tools have been integrated into FHWA s Interactive Highway Safety Design Model (IHSDM). IHSDM is a suite of software analysis tools developed by FHWA that are used to evaluate the safety and operational effects of geometric design decisions on highways (). IHSDM applies HSM methodologies to estimate safety performance. It can be used to provide estimates of a highway design's expected safety and operational performance and checks existing or proposed highway designs against relevant design policy values (). The Highway Capacity Manual (HCM), published by the Transportation Research Board (TRB), presents the operational performance measures and evaluation
Hermanus Steyn and Julia Knudsen 0 procedures for various modes and types of facilities. The HCM includes methodologies for evaluating the operations of freeways, weaving areas, freeway/ramp junctions, two-way two-lane facilities, and intersections (). For users in Montana, MDT s Safety Information Management System (SIMS) is a database and analysis system that allows users to screen the roadway network and complete reviews of specific locations using HSM tools and methodologies. This system provides increased access to crash data and advanced crash data query capabilities. SIMS incorporates many roadway elements into the database, which allows for comparisons of crashes versus roadway characteristics. In addition, this system allows tracking of safety projects for before and after evaluations. A performance-based road design approach can be beneficial to executing design decision documentation. The steps taken within this approach help identify the need for design exceptions early in project development. It provides a clear way to document design decisions and the considerations supporting those choices that result in a flexible design solution. Documenting design decisions helps manage tort liability risk. The MDT project development process is similar to national recognized project development processes. The majority of MDT projects are developed from the planning stage to the construction stage by the same design team. The typical activities within a MDT project are executed through four primary stages: Scoping, Design, Right-of-Way, and Construction. Figure illustrates where MDT s project development process, the nationally recognized project development process, and performance-based road design approach coincide with each other. Throughout the chapters, designers are reminded of the applying the performance-based road design approach to assist documenting their decisions. A performance-based design approach and the tools presented in this approach, provide an effective way to evaluate the performance measures, understand the tradeoffs of design decisions, and document the process. 0 FIGURE - Relationship between Project Development Processes (RDM Exhibit -).
Hermanus Steyn and Julia Knudsen 0 0 0 OVERVIEW OF CHAPTERS AND SUPPLEMENTAL DOCUMENTS This section highlights key information that is documented in the respective chapters and supplemental documentation. As part of the RDM development, KAI also collaborated with MDT staff to develop a stand-alone MDT Geometric Design Standards document that summarizes all of the design standards for MDT facilities (). The RDM references this document regularly to encourage designers to understand the background and principles, while also referencing the criteria recommended and required by MDT. Chapter - Road Design Guidelines and Procedures Chapter introduces the RDM by describing the manual s purpose, scope, and primary definitions. This chapter presents the nationally recognized perspective of the project development process and introduces topics such as performance-based road design and multimodal design considerations. The chapter includes an overview of MDT road design activities, process, and project coordination. This chapter sets the basis for the entire manual by outlining key concepts and providing a fundamental understanding of the design policies and procedures for executing a design project within MDT. Highlights: A key objective was illustrating how the MDT design process aligns with the nationally recognized project development process, as well as implementing a performancebased design approach. This chapter highlights current research and performance tools (,,,) that may help a designer understand the tradeoffs between design, safety and operations. Chapter - Basic Design Controls Roadway design is predicated on basic controls that establish the overall objective of the highway facility and identify the basic purpose of the highway project. Understanding the distinction of the basic design controls and geometric design criteria is fundamental to executing a design approach that meets the desired outcomes of a project. The design controls are attributes, values, or qualities that influence discrete geometric element dimensions or considerations. Design criteria are dimensions and values that meet design control needs, such as curve radius, cross-section, and merge lengths. The chapter outlines the basic design controls for the criteria that impact roadway design. This includes a discussion on the functional classification system, speed, traffic volume controls, access control, sight distance, and the design exception process. This chapter consistently references the MDT Geometric Design Standards that present design criteria for the design controls (). Identifying the controls that impact the criteria can help a designer understand how the design decisions can impact the performance measures related to the overall project desired outcomes. Highlights: Chapter emphasizes the idea that the design controls and associated criteria provide a platform for the designer to make thoughtful evaluations of the project needs and context. Design decisions may result in changing various design criteria to achieve the overall purpose of the project and/or more effectively serve the various users of the facility. The design exception process is meant to help document the design decisions (changes to criteria based on project context) and provide a framework for balancing the importance of geometrics, safety, and operations, as well as considering tradeoffs and integrating performance-based design.
Hermanus Steyn and Julia Knudsen 0 0 0 Chapter Horizontal Alignment The horizontal alignment of a roadway, as well as the vertical alignment and cross section, will have an impact on the safety and operational performance for various road users, as well as construction and maintenance costs. This chapter presents the basic design principles for designing horizontal alignment elements, including a discussion of the different types of horizontal curves and methods of achieving superelevation. Highlights: A key element of Chapter was updating the information in this chapter to be consistent with the most recent version of the American Association of State Highway and Transportation Officials (AASHTO) A Policy on Geometric Design of Highways and Streets (Green Book) (). This chapter starts by explaining the design principles and approach related to horizontal alignment design and reminds the designer how to integrate performance-based design into projects. In addition, this chapter clarifies MDT s recommended method for superelevation axis of rotation. Chapter Vertical Alignment The roadway vertical alignment may play an important role in a roadway's safety, aesthetics and project costs. This chapter provides guidance on vertical alignment elements including: coordination with other design elements; laying out a profile grade line; guidance on grades including a range of allowable grades; principles and application of vertical curves; and minimum vertical clearances. Highlights: Chapter starts by explaining the design principles and approach related to vertical alignment design as well as provides a discussion on the coordination of horizontal and vertical alignment that should be integrated to enhance safety and improve operations. Chapter Cross Section Elements The roadway cross section can play an important role in the basic operational and safety features for the roadway and has a significant impact on the project cost, especially for earthwork. This chapter provides guidance in the design of cross section elements, including the roadway section, shoulders, bicycle lanes, two-way left-turn lanes, on-street parking, curbs, sidewalks, medians, landscape areas, and side slopes. In addition, this chapter provides several typical sections for various roadway types. Highlights: The development of Chapter included new, enhanced sections on key design elements such as dedicated bicycle facilities, pedestrian facilities, and the use of speed reduction treatments. This chapter starts by explaining the design principles and approach related to cross sectional elements and reminds the designer how to integrate performancebased design into projects. Chapter Intersections and Interchanges Intersections and interchanges are an important part of the transportation system. These intersection nodes create access and provide mobility on a facility; however, they are also a location of inherent conflict. The operational efficiency, capacity, safety, and cost of the transportation system depend largely upon their respective designs, especially in urban areas. The primary design objectives of intersections and interchanges are: Minimize the potential for and the severity of conflicts among motor vehicles, bicycles, and pedestrians; Provide for the convenience, ease, and comfort of all users;
Hermanus Steyn and Julia Knudsen 0 0 0 Provide adequate capacity; and Examine potential system-wide impacts, especially for new construction. Chapter discusses the geometric design of at-grade intersections typically conducted by the road designer including intersection traffic control, intersection alignment, intersection profile, and turning radii. It provides an overview of lanes at intersections, approaches, multimodal design considerations, speed reduction treatments, as well as alternative forms of intersections, including roundabouts, and interchanges. Highlights: One of the key components of this chapter was understanding and emphasizing the coordination between the MDT Road Design Section and the MDT Traffic and Safety Bureau. The Bureau plays a significant role in intersection and/or interchange design and is responsible for the operational and safety analyses. Information in this chapter was closely coordinated with the MDT Traffic and Safety Bureau to maintain coordination and communication between the entities and encourage consistency. Chapter Multimodal Design Considerations The explicit design for all modes of travel is an integral part of a roadway project and has an impact on the safety and operational performance for various road users. This chapter presents the basic design principles and approach for designing multimodal design elements, including pedestrian facilities, bicycle facilities, shared used paths, crossing treatments, and transit facilities. This chapter emphasizes the need to coordinate with the Traffic and Safety Bureau and Planning Division to obtain an understanding of local plans, operational and safety aspects, as well as the traffic engineering design elements for signing and pavement markings associated with the multimodal design. Highlights: Chapter was a new chapter and provided a toolbox of multimodal design treatments for bicycles, pedestrian, and facilities, as well as crossings. Each treatment described provides different levels of separation. The level of separation depends on the functional classification of the roadway, traffic speed, as well as the traffic, bicycle, and pedestrian volumes along the facility. For example, a high-volume, high-speed arterial is also serving a bicycle and pedestrian recreational route, then physical separation (e.g., landscaped buffer, concrete barrier, etc.) would be appropriate. The chapter emphasized the need for designers to consider the level of separation that appeals to a wide variety of users based on the project context and future vision of the facility. Chapter Urban Design Considerations Chapter is intended to provide design guidance for urban facilities including local streets, collectors, and arterials. The design approach described in this chapter considers various transportation modes and addresses how a designer can effectively integrate vehicles, pedestrians and bicycles into the urban environment. This chapter will: Reference the tools and urban design considerations described in Chapter, Provide additional information on urban intersections to expand on Chapter, Apply the basic roadway design principles documented in Chapters,, and, and Introduce drainage topics that are further discussed in Chapter. Highlights: Chapter was a new chapter in the RDM. While traditionally many of the MDT projects may have been focused in primarily rural areas, this chapter provided an opportunity to highlight some of the unique urban design features.
Hermanus Steyn and Julia Knudsen 0 0 0 0 Chapter Roadside Safety The ideal roadway would be free of obstructions or other hazardous conditions within the entire highway right-of-way. However, this may not be practical because of economic, environmental, or drainage factors. Chapter presents the design principles and guidance for roadside safety. This includes information on clear zone distances, which are designed to adequately provide a clear recovery space for the majority of drivers who run off the road. This chapter also provides criteria for the use of roadside barriers, median barriers, breakaway devices, and impact attenuators where providing the clear zone is not practical. Highlights: One of the key components of Chapter was updating the information to be consistent with the most recent version of the AASHTO Roadside Design Guide (). Chapter 0 Work Zone Traffic Control Traveling through a construction zone can be difficult and confusing to drivers. A well-planned traffic control plan can alleviate many of these difficulties and confusions. This chapter provides information for the road designer to develop a safe and well-conceived transportation management plan including construction options, geometric design of crossovers and detours, and roadside safety through construction zones. Highlights: Chapter 0 relied heavily on referencing the other chapters for specific design information and understanding how that would be integrated into the work zone traffic control. One of the key elements of this chapter was understanding the design coordination that takes place and confirming this process with MDT s current practice. Chapter Drainage and Irrigation Design Chapter presents principles and criteria for the design and consideration of drainage facilities in collaboration with the roadway design; including: culverts, special-purpose large culverts, storm drains, roadside drainage, miscellaneous drainage facilities, irrigation facilities, and encasement pipes. The development of Chapter was coordinated closely with the MDT Hydraulics Manual and the MDT Permanent Erosion and Sediment Control (PESC) Design Guidelines to provide consistency to designers in these references. Highlights: This chapter was closely coordinated with the MDT Hydraulics Section, which initiated productive discussions between the various departments. It was important to provide information that was useful and relevant to the road design designer and process. Chapter Plan Preparation Chapters through provide the designer with uniform criteria and procedures for the geometric design of a highway facility. These roadway designs must be incorporated into the road plans so that they can be clearly understood by contractors, material suppliers, and construction personnel assigned to supervise and inspect the construction of the project. To
Hermanus Steyn and Julia Knudsen 0 0 0 provide this consistency, this chapter provides guidelines for the uniform preparation of contract plans including recommended plan sequence, drafting guidelines, plan sheet content and sample plan sheets. Highlights: A unique attribute of Chapter was receiving input from the MDT personnel that actually conduct the plan reviews and work with the designers on the final development of plan preparation. Chapter Quantity Summaries In addition to preparing clear and concise construction plans, the designer needs to compile an accurate estimate of the project construction quantities. This information leads directly to the Engineer's Estimate, which combines the computed quantities of work and the estimated unit bid prices. An accurate estimate of quantities is critical to prospective contractors interested in submitting a bid on the project. Chapter presents detailed information on estimating quantities for highway construction projects. Highlights: MDT emphasized that this is the most critical chapter for the RDM, in terms of what will be most often used and referenced by designers. The key objective was to update this chapter to be user/designer-friendly and provide useful guidance. Chapter Specifications/Special Provisions/Detailed Drawings Contractors, material suppliers, and MDT personnel assigned to supervise and inspect the construction of the project use the Standard Specifications for Road and Bridge Construction (Standard Specifications), Supplemental Specifications, Special Provisions and the MDT Detailed Drawings to assist them in the project design and construction. Chapter describes the purpose of the specifications, special provisions and detailed drawings, as well as presents the guidelines for preparing Special Provisions. Highlights: Chapter outlines the additional design information that is required and consistently referenced during a design project. Appendices The purpose of the RDM is to provide uniform design practices for design teams preparing contract plans for projects involving MDT facilities. While the majority of the information can be found in the design manual chapters, additional design definitions, details, guidance, and example calculations are provided in the appendices. The appendices are separated into two parts: Appendices A J consist of additional chapter content, which includes supplemental design guidance, detailed equations and descriptions associated with various manual chapters. Appendix K consists of example calculations for designers to reference during project computations. The examples are numbered based on the corresponding chapter content. For example, Example. corresponds to material in Chapter. Highlights: The appendices were developed to provide supplemental information associated with specific chapters and provide actual design examples that designers could reference. The examples may also be used as training tools for new designers.
Hermanus Steyn and Julia Knudsen 0 0 0 Geometric Design Standards The MDT Geometric Design Standards provide design criteria summary tables for the geometric design of MDT rural and urban facilities (). Chapter outlines the basic design controls for the criteria presented in this document. The selection of design values depends on the functional classification of the highway facility, which is provided in Chapter.. Highlights: While this was previously part of the RDM chapter content, these standards are now a stand-alone document separate from the RDM, but consistently referenced. These standards were updated to reflect consistent design criteria for each type of MDT facility for both rural and urban areas. The standards were also updated to reflect a consistent terminology and organizational structure for the design elements presented in the Design Exception Template. This allows designers to easily work with both documents to identify any design elements that may require additional documentation. Design Exception Template The designer is responsible for making every reasonable effort to meet these criteria in the project design (). However, this will not always be practical or appropriate. The performancebased design approach will guide the designer to take the project context and the intended project outcome into account when establishing the design controls and associated design criteria on a project-by-project basis. The design decisions can be documented through design exceptions. This template discusses MDT's procedures for identifying, justifying and processing design exceptions. The following provide the outline of the template and highlights sections where to integrate performance-based design as part of the documentation process:. Executive Summary The executive summary should describe the reason for seeking a design exception, and provide a description of the features that will require an exception to the approved design standards.. Proposed Project This section should describe the proposed project, its purpose and intended outcomes, as well as clearly outline the benefits this project will have on the overall transportation system highlighting the overall performance of the system.. Existing Conditions This section should address the existing conditions in which the project is being proposed, and provide the context to better understand the potential impact of the design exception... Roadway character.. Description of surrounding area: This subsection should describe the characteristics of the surrounding area, such as urban/rural classifications, terrain (e.g., flat, rolling, mountainous), and surrounding land uses. In addition and if applicable, it may summarize the future vision for the area, because the context of the surrounding area may result in a change in roadway character (e.g., rural to urban)... Safety.. Environmental factors.. Cultural resources.. Public perception
Hermanus Steyn and Julia Knudsen 0 0 0. Description of Design Exception and Applicable Criteria. This section should address the design exception being requested. In the case that there are multiple design exceptions being submitted for the same project, each design exception request should be addressed separately in this section, but discussion should be provided describing how multiple design exceptions relate to one another directly or indirectly, particularly if there is a cumulative effect. Description of the proposed value of the criteria for the project and why it is appropriate for the project context and how it is consistent with the purpose and need (i.e., performance-based design original intended outcome).. Impacts This section should address the anticipated cumulative effects of the design exception on corridor operations, safety, adjacent sections, as well as long and short-term effects. This section should integrate performance-based design into the evaluation. o Analysis of impact on corridor operations: Level-of-service, volume-tocapacity ratio o Analysis of impact on corridor safety: The Highway Safety Manual (HSM) procedures may be used, when applicable, to compare predicted safety for alternative scenarios () o Adjacent roadway sections and future work plans: Discussion of compatibility with adjacent roadway sections and anticipated future corridor improvements o Review of impact to driver expectation: Considering adjacent roadways and other planned improvements; and Consider the overall context of the roadway o If the design exception is for design speed, include a discussion of effects on other controlling criteria determined by design speed. For example; Horizontal curves and superelevation; Stopping Sight Distance; and Clear zone. Alternatives Considered This section should include a description and explanation of any feasible alternatives that were considered, the selected treatment, and the reasons why the proposed treatment was selected.. Mitigation Measures This section should address all mitigation efforts for the impacts identified in the Impacts section. These should include any mitigating features proposed within the design, whether incidental or added exclusively to mitigate the nonconforming element, as well as any mitigating circumstances outside of the design. The FHWA document, Mitigation Strategies for Design Exceptions may be a resource; it provides potential mitigation measures for various design elements (0).. Anticipated Costs This section should address the anticipated costs and cost savings associated with the design exception. Costs include costs to the department, as well as social costs to society. Not all costs can be easily determined or measured in dollars, however costs included in this section should be quantified to the extent practical and qualified as real, potential, and/or comparative. These can be documented using a benefit-cost analysis.
Hermanus Steyn and Julia Knudsen 0 0 0. Recommendation/Summary This section should summarize the information from the previous sections and recommend the proposed design exception. The summary must show that reasonable engineering judgment was used to justify the proposed design exception and the outcome will match the project purpose and need. Design exception processes represent a means for designers to implement design features that do not fall within the designated design criteria established by MDT. Historically, design exceptions yielded projects, as states began to face the challenges of redesigning existing roadway facilities within an environment of increasing constraints. In essence, it is a form of documentation that shows the analysis and engineering judgment performed to design a roadway to fit the surrounding environment and local context. As roadway networks become more built-out and the surrounding land uses make certain roadway improvements impractical, design exceptions will become increasingly embraced as a process with which to implement customized and flexible designs to better meet the needs of a constrained environment. Highlights: The design exception template was updated to provide consistency with the MDT Geometric Design Standards and emphasize the need to identify the tradeoffs between design, safety and operations. This guides designers to consider how applying a performancebased design approach will help document the design decisions. CONCLUSIONS The two-phase project approach provided a systematic approach for updating the road design manual: Phase I established an agreed upon annotated outline for the road design manual update. The objective was to proceed forward from Phase I as a foundation with limited revisions within the overall approach avoiding approach change and to be cost effective. Phase II captured the production of the manual in manageable bundles to help the project team (preparers and reviewers) continued to be efficient throughout the project duration. At the start of each bundle, the project team confirmed the approach to be consistent with the Phase I annotated outline and established deliverable dates consistent with the overall project schedule. A unique objective of the new MDT RDM was to incorporate a performance-based road design approach into the road design project development process that enables designers to make informed decisions about the performance tradeoffs, which is referenced throughout the manual. The new manual explains the engineering principles and approach, as well as provides standards in applying research-based design guidance. This paper could serve as a model for other State Departments of Transportation in the development of their new design manuals to reflect performance-based design. ACKNOWLEDGEMENT The material represents excerpts from the new Road Design Manual, which was prepared for Montana Department of Transportation (MDT).
Hermanus Steyn and Julia Knudsen 0 0 REFERENCES ) Montana Department of Transportation (MDT). Road Design Manual (RDM). MDT. (). http://www.mdt.mt.gov/publications/manuals.shtml#rdm ) Ray, B., Ferguson, E., Knudsen, J., Porter, R.J., and Mason, J. NCHRP Report : Performance-Based Analysis of Geometric Design of Highways and Streets. Transportation Research Board. (). ) Montana Department of Transportation (MDT). Geometric Design Standards (GDS). MDT. (). http://www.mdt.mt.gov/other/webdata/external/cadd/rdm/standards/geo METRIC-DESIGN-STANDARDS.pdf ) American Association of State Highway and Transportation Officials (AASHTO). A Policy on Geometric Design of Highways and Streets. AASHTO. Washington, D.C., () ) American Association of State Highway and Transportation Officials (AASHTO). Roadside Design Guide, th Edition. AASHTO. Washington, D.C., (). ) Montana Department of Transportation (MDT). Design Exception Template. MDT. (). i. Not published/posted yet, but will be into MDT s report templates. ) American Association of State Highway Transportation Officials (AASHTO). Highway Safety Manual (HSM). AASHTO, Washington, D.C., (0). ) FHWA. Interactive Highway Safety and Design Model (IHSDM). FHWA, Washington, D.C., (0). ) Transportation Research Board (TRB). Highway Capacity Manual (HCM). Transportation Research Board of the National Academies, Washington, D.C., (0). 0) Stein, W. J., and T. R. Neuman. Mitigation Strategies for Design Exceptions. Report No. FHWA-SA-0-0. Federal Highway Administration, Washington D.C., (0).