Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
56 CHAPTER FOUR CONCLUSIONS This synthesis is based on a literature review and survey responses from 43 agencies (41 state transportation agen- cies (STAs), the District of Columbia, and Puerto Rico). The literature review focused on key publications outlining the conventional approach to design as well as the newer con- text-sensitive solutions/context-sensitive design (CSS/CSD) and performance-based planning approaches. It also incor- porated publications that outlined complimentary fields that could be used to evaluate trade-offs such as value engineer- ing (VE), choosing by alternatives (CBA), risk analysis and management, and safety. Rather than an exhaustive litera- ture search on a single topic area, the synthesis attempts to present an overview of the wide range of techniques avail- able from the highway design and related fields and how they relate to trade-off analysis. SURVEY RESULTS One of the key issues identified by the survey was that few STAs have codified procedures for evaluating trade-offs in highway geometric design. Based on the input received, the majority of the time agencies surveyed conduct trade-off analyses they had to rely on engineering judgment. Most agencies evaluate trade-offs during preliminary engineering or environmental clearance. However, several agencies pointed out that trade-offs often are not raised until a design is nearly complete. One of the difficulties cited that contributed to this situation was the lack of design resources and decision makers available in the predesign period of project development to undertake trade-off decisions. How- ever, the later in the project development process that trade- off decisions are made, the more limited the flexibility in dealing with them becomes. The majority of agencies utilize consultant staff as the primary resource for conducting trade-off analyses and have centralized approval authority for decisions regarding the outcomes. Further, different units in the agency are respon- sible for approving trade-offs and design exceptions. During the development of the survey, 11 typical catego- ries of trade-offs were identified for inclusion in the survey instrument: access management, cost, environmental issue, historic impact, human factors/driver expectancy, opera- tional efficiency, right-of-way (ROW) availability, safety, schedule, social concerns and tort liability exposure. With the exception of tort liability exposure, agencies responded that all of these trade-offs were typically considered as goals within a Purpose and Need (P&N) statement. Safety was overwhelmingly identified as the trade-off most used as justification for design decisions. Addition- ally, cost and environmental issues have a high likelihood of being used to justify design decisions. This shows that while a number of trade-offs are considered when making design decisions, agencies tend to focus on these three most often. Continuing this trend, when asked to rank the likelihood of a trade-off being accepted as justification for a design decision, safety, cost, and environmental issues were identi- fied as being likely to be accepted. Justifications associated with historic impact, operational efficiency, and ROW avail- ability also were likely to be accepted. Approximately half of the agencies believed there were gaps or missing components in the STAâs procedures and tools associated with evaluation of trade-offs in design. Some of the concerns identified were associated with a con- cern that the lack of formal guidance and procedures forced a reliance on engineering judgment. Weaknesses of this approach are limitations associated with inexperienced staff, inconsistencies associated with informal practices, failure to adequately identify and consider appropriate trade-offs, and inconsistencies in documentation of decisions. Conversely, agencies that did not believe there were gaps often pointed to processes and policies that, when followed, minimized gaps. Approximately three-quarters of the agencies did not have risk prediction tools or techniques to assist in balanc- ing competing interests in the design process. Those that did have tools in place almost all used ones that combine a mix- ture of qualitative and quantitative analyses. Approximately half of the agencies have some tools and training to assist designers in evaluating trade-offs in the design selection process. Common tools identified are the Highway Safety Manual, IHSDM, RSAP, VE, crash history, life-cycle cost analysis, and a design policy manual.
57 Only five agencies have developed specific performance goals regarding the evaluation of trade-offs. Shoulder width was overwhelmingly the controlling cri- terion most often associated with a design exception request. Other controlling criteria typically associated with design exception requests are horizontal alignment, vertical align- ment, and lane width. The controlling criterion of structural capacity was not selected by any respondent, and several respondents added notes to the survey responses that this criterion would never be considered. When asked to rank how willing the agency typically is to consider a design exception for each of the 13 control- ling criteria, shoulder width, horizontal alignment, verti- cal alignment and lane width were identified as likely to be considered. Approximately three-quarters of the agencies had no plans to reevaluate how trade-offs are handled in the design selection process in the next 6 to 12 months. Further, approx- imately 90% of the agencies had no plans to reevaluate how design exceptions are handled over the same period. LITERATURE REVIEW The current edition of the Green Book is the basis for most of the design criteria used by STAs. The broad policy-level overview of trade-off considerations in the Green Book points out that the guidance is intended to provide opera- tional efficiency, comfort, safety, and convenience for the motorist, while taking into consideration environmental quality. Further, the effects of the various environmental impacts can and should be mitigated by thoughtful design processes. However, the guidance speaks to the evaluation of trade-offs only in general terms at a fairly high level and does not provide specific cause-and-effect examples. Fur- ther, as the guidance has developed, much of the background material regarding how standards have been developed has been removed, making it more difficult for practitioners to establish these relationships. To evaluate the trade-offs associated with design, the designerâs understanding of the basic controls and criteria associated with each element of the design is important. Although the Green Book provides little guidance on evalu- ating these trade-offs, it does establish the framework from which most controls and criteria are derived. Design criteria, established through years of practice and research, form the basis on which highway designers strive to balance competing needs for a roadway project. For many situations, there is sufficient flexibility within the design cri- teria to achieve a balanced design and still meet minimum values. On occasion, designers encounter situations with especially difficult site constraints, and an appropriate solu- tion may suggest the use of design values or dimensions out- side the normal range established by a control or criterion. In such cases, a design exception may be considered. Docu- mentation of design exceptions is important to verify that sound engineering judgment and social/cultural impacts have been considered and that the proposed solution demon- strates an appropriate balance of these components. To help overcome some of the limitations of the conven- tional approach to highway design as presented in the Green Book, FHWA produced Flexibility in Highway Design in 1997. The guide does not attempt to create new standards. Rather, it builds on the flexibility in the current standards to identify opportunities to use flexible design as a tool to help sustain important community interests without compromising safety. CSS and CSD both consider the overall context within which a transportation project fits. The conventional approach to design does not emphasize an interdisciplin- ary approach, although the CSS/CSD approaches do. As the design process evolves, consideration given to issues that do not center on design criteria becomes increasingly important to determining the ultimate success of a design. This increases the need to identify trade-offs associated with design decisions accurately and completely and strike a balance between the competing factors in an interrelated decision-making process. Because successful projects will require a level of compromise and trade-off, CSS/CSD are excellent tools for providing structure to the process. The concept of context-based design is closely related to CSS/CSD. However, context-based design implies that the street or road is designed to be fully compatible with its context. In context-sensitive design, in contrast, context is taken into account but is not necessarily a governing factor in the design. Flexibility in the application of design criteria requires a fundamental understanding of the basis for these criteria (i.e., basic design controls) and the impacts of changing the dimensions of a criteria or adding/eliminating design ele- ments. It is critical that trade-offs associated with these decisions be fully understood to preserve the integrity of the resultant design. The analysis of trade-offs is central to the alternatives analysis process of any project. The goal of an alternatives evaluation is to provide an objective and balanced assess- ment of impacts, trade-offs, and benefits of each alternative. This requires careful selection of, and stakeholder agree- ment on, measures of effectiveness (MOEs) to be used as evaluation criteria. The MOEs need to reflect community and environmental objectives as well as transportation. Once the alternative analysis is completed, one of the crit- ical aspects of trade-off decisions is ensuring that adequate
58 documentation of the decision occurs and that the docu- mentation is retained, as both crashes and tort claims may occur many years after the decisions and construction. As important as adequate documentation is a clearly understood decision process. Projects are made up of a series of tasks, each of which may involve a series of trade-off decisions that result in a final project decision outlining the ultimate action to take. As such, it is critical that the decision process identify what decisions will be made and by whom, and what analyses, processes, and documents will be produced to sup- port important decisions. Several other closely related fields have insight to offer in the treatment and evaluation of trade-offs in a decision- making process and in how that process can be structured to ensure the best decisions. Many of the tools, techniques, and processes are currently utilized as part of the transportation field and can be adapted for use in trade-off analysis. Some agencies have begun to incorporate the following into every- day operations: ⢠Performance-based planning has most often been applied at the organizational level to assess program conformance with a stated overall transportation plan or goals and objectives. However, the process is just as applicable for evaluating trade-offs associated with alternatives, especially when put in the context of CSS/ CSD. The use of outcome-based performance mea- sures, as opposed to the traditional use of output-based performance measures, is especially apt for evaluating trade-offs. ⢠The VE process is a powerful decision-making pro- cess, as using the common language of functions enables an interdisciplinary team to communicate more effectively to arrive at a supportable decision. One of the challenges in using VE principles to make trade-off decisions in design is associated with the dif- ficulty in monetizing key factors under consideration (e.g., quality of life factors). ⢠The CBA process assists decision makers in mak- ing informed choices on program expenditures. CBA differs from other decision-making systems in that it concentrates only on the difference between the advan- tages of alternatives being compared. The CBA pro- cess provides a logical, trackable linkage between the factors used to identify the preferred alternative and the major trade-offs among the alternatives considered. Risk is perceived as the effect of uncertainty on a proj- ect or organizational objectives and represents exposure to mischance, hazards, and the possibility of adverse conse- quences. A risk can be acceptable for inclusion on a project when the risk is within acceptable tolerance and is balanced by a desirable benefit. As such, the principles of project risk analysis, risk and reliability analysis, and risk management may be used to support decision making regarding the trade- offs between various alternatives. Promoting safety and safe travel is at the core of all trans- portation planning and design, where safety can be under- stood as a measure of the freedom from unacceptable risks of personal harm. The basic principles and guidelines that influence much of what happens in project development are founded on professional principles of encouraging safe design. As such, trade-offs may influence the safety poten- tial of an alternative. Several key areas provide insight into how to address these trade-offs: the field of organizational accident analysis and prediction, safety-conscious planning, Road Safety Audits, the interactive highway safety design manual, and the new Highway Safety Manual. FUTURE NEEDS Preparation of this synthesis revealed significant needs asso- ciated with developing tools and formalized processes for dealing with trade-offs in highway geometric design. The STA survey identified several key areas that need additional research and development. The recent release of the Highway Safety Manual and the commitment to continue to develop this resource to expand its coverage into additional roadway types will pro- vide an additional resource to agencies conducting trade-off analyses that focus on safety. The ability to utilize scien- tific, data-based analyses to make performance-based deci- sions regarding the impacts of trade-offs on to safety should greatly increase designersâ ability to understand the true impacts of their decisions. VE is a useful process to ensure that the alternative selected provides the needed functions of a project at the lowest cost, while improving the quality and value of the project and reducing the overall time to complete the project. However, a number of agencies still view VE as a âcheck- boxâ activity and not as a vital tool to help ensure that trade- off analyses support the agencyâs vision and the projectâs purpose and need. The development of risk-based methods to account for both quantitative and qualitative factors in the analysis of trade-offs is necessary to fully understand the impacts of design decisions on environmental issues. The use of interdisciplinary teams has proven effective in areas such as Value Engineering, Road Safety Audits, and Context Sensitive Solutions/Context Sensitive Design. Upcoming research for NCHRP 17-53, Evaluation of the 13 Controlling Criteria for Geometric Design, should
59 add much-needed clarification to the safety and opera- tional impacts of trade-offs associated with these criteria. Safety is a key rationale for all the controlling criteria except structural capacity and vertical clearance. However, the 13 controlling criteria were established at a time when safety relationships for these elements were poorly understood, and these criteria and their application have not been reconsid- ered as new knowledge has been gained about the relation- ships between geometric design elements and operations. It is hoped that this research will address questions regarding whether changes are needed in the list of design elements considered as controlling criteria and whether the list of design elements considered as controlling criteria might vary between roadway types. One of the core principles of CSS/CSD is to ensure that all stakeholders are part of the decision-making process and feel a true sense of ownership of the outcome. This does not mean that agencies abdicate their decision-making powerâ the agency has the final call. However, it does ensure that the trade-off analysis is conducted in such a way as to inform all stakeholders (including the public informing the agency) of the needs and expectations of the other involved parties and the benefits and drawbacks of the many elements fre- quently included in transportation projects in order to gain a full understanding of the implications of the trade-off deci- sions. However, the results of the survey showed that three- quarters of the responding agencies did not have a role for public involvement in the approval of trade-offs. CSS/CSD principles and practice have been developed and successfully implemented over the past two decades. The CSS/CSD principles have been accepted to varying degrees by the transportation professional community and decision makers. Based on agency responses to the survey, consultants handle the completion of the trade-off analysis most of the time. As such, these consultants become the ultimate users of the tools and policies produced to guide trade-off consid- erations. The inclusion of key consultants in the development of these tools and procedures during agency development will result in a better product that can be more easily inte- grated into everyday practice. Just as the application of prin- ciples of CSS/CSD are successful only through the use of a interdisciplinary team that includes representatives of all key stakeholders, the same is true for the development of the tools and procedures to support CSS/CSD. FUTURE RESEARCH Preparation of this synthesis revealed further research needs associated with evaluation of trade-offs in highway geomet- ric design. Several topics emerged as areas of interest for future study: ⢠Tools and a Formal Process for Evaluating Trade- offs. A number of survey respondents indicated that the approach to trade-off analysis identified a lack of formal tools, including risk prediction tools, proce- dures, and policies. Further research could provide a guidebook to codify tools and processes to evaluate trade-offs. ⢠Online Resources for the Green Book. The basis of many design criteria has been removed from the dis- cussion presented in the Green Book, and designers are responsible for determining which design values directly support substantive safety. A successful approach for providing background materials is illus- trated by Volume 4 of the 2010 Highway Capacity Manual, an electronic-only volume that registered users can access online. This volume features sup- plemental chapters on methodological details, com- prehensive case studies, and a technical reference library that includes the research studies used to develop the manual. Further research could include development of a similar electronic resource to sup- port the Green Book. ⢠Impact of Design Consistency. One of the tensions between the traditional Green Book approach and the flexible approach to roadway design associated with CSS/CSD is centered on the concept of design con- sistency. Further research could include a study of the safety impacts of design consistency. ⢠Highway Safety Manual. Further research to expand the number of facility types for which the HSM pro- cedures can be used may provide designers with addi- tional tools for considering trade-offs. ⢠Integration of Project and System Level Trade-offs. Further research could describe the relationships between project- and system level-trade-offs.
