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|Federal Highway Administration > Publications > Public Roads > Vol. 73 · No. 4 > Risking Success Through Flexible Design|
Publication Number: FHWA-HRT-10-002
Risking Success Through Flexible Design
by Keith Harrison and Stephanie Roth
For many years, the customary approach to highway project development had been for engineers to gather information, make independent decisions, and then announce and justify their design plans to the public, known informally as the "decide, announce, defend," or "DAD," approach. The prevailing thinking was that highly trained engineers applying standard designs were producing projects that best served the needs of the traveling public. Projects were by and large being delivered on time and within budget, and project goals such as reducing crashes and congestion and maintaining the infrastructure also were being realized.
However, in recent years, State departments of transportation (DOTs) and professional engineers using the DAD approach have run into resistance from the public and stakeholders concerned about community interests. According to the Transportation Research Board's (TRB) National Cooperative Highway Research Program (NCHRP) Report 480, A Guide to Best Practices for Achieving Context Sensitive Solutions, this is particularly true when highway projects are perceived as having clear and measurable adverse impacts on the communities through which they pass.
"Such an approach is no longer feasible in today's professional climate," says Federal Highway Administration (FHWA) Associate Administrator for Infrastructure King Gee, "nor should we continue to use it. The public will no longer unquestionably accept project proposals, regardless of how well thought out they are. Rather, it is crucial to involve the public early in the process, and keep them involved, to reach a consensus that is acceptable to everyone."
With the expanding role of public involvement and the push to address concerns beyond engineering in highway projects come added responsibilities and considerations. Today, highway designers face many complex tradeoffs. A quality design requires thoughtful consideration of the needs of a variety of users, and it has to balance cost, safety, and mobility with historical, cultural, and environmental impacts. A quality design is more than simply assembling elements using standard plans or charts from a design manual. Highway engineers and designers need to understand the complex relationships between their design choices and the related risks.
Over the past decade, through conferences, training, and new partnerships, FHWA and its partners have been working to bridge knowledge gaps and enable transportation planners and engineers to design with flexibility and employ context sensitive approaches with greater confidence and regularity.
Understanding this evolving landscape of flexible and context sensitive highway design and how to thrive in it will enable State DOTs to build and refine roads and other transportation facilities that not only meet safety and mobility requirements but also help create more livable communities.
Early Calls for Flexibility
Some in the engineering community long have recognized the need for flexibility in highway design. Engineering journals from nearly a century ago cautioned against over-reliance on rigid application of design standards. For example, in "The Use and Abuse of Road Standards," an article in the August 1914 issue of Engineering and Contracting, the authors concluded that "standards are merely recommended designs which are to be adhered to unless conditions indicate that a variation in the design would meet them better..[T]o neglect the detailed study of local conditions.often results not only in an unwarranted increase in.cost, but may result in a type of construction which fits poorly the location where used."
The American Association of State Highway and Transportation Officials (AASHTO) built on this philosophy in the 1973 edition of its publication A Policy on Design of Urban Highways and Arterial Streets (also known as the "Red Book"). In the preface, AASHTO encouraged a tailored approach: "Good design will not necessarily result from direct use of the policy values. To form a segment of highway that will be truly efficient and safe in operation, be well fitted to the terrain and other site controls, and be acceptably amenable to the community environment, it must be a carefully tailor-made design for the unique set of conditions along the segment."
With passage of the National Environmental Policy Act of 1969, transportation agencies began addressing the possible adverse effects of transportation projects on the environment. But it took the U.S. Congress's recognition of the need for flexibility in design--and the benefits--to help what would later become known as context sensitive solutions (CSS) gain traction in project development.
In the landmark 1991 Intermodal Surface Transportation Efficiency Act, Congress emphasized the Federal commitment to preserve historic, scenic, and cultural resources affected by transportation projects. The National Highway System Designation Act of 1995 went a step further, stressing the need for flexibility in highway design to promote preservation of historic and cultural resources.
These legislative mandates led to the FHWA publication Flexibility in Highway Design (FHWA-PD-97-062), which underscored the importance of balancing the need for highway improvements with the need to integrate a project's design into the surrounding human and natural environments. Published in 1997 in partnership with AASHTO, the National Trust for Historic Preservation, and the nonprofit Scenic America, the document laid out a challenge for the highway design community: Use more innovative thinking and creativity to find and tailor design solutions to address the varied, and often conflicting, objectives of road projects. Flexibility in Highway Design emphasized that each project is unique, with its own distinct context, circumstances, and local characteristics. Further, the report stipulated that to balance a project's needs with its context, "designers need flexibility."
Then, in 1998, the Maryland State Highway Administration (SHA) hosted a national conference, "Thinking Beyond the Pavement," which brought together a diverse group of stakeholders to frame the overarching principles of context sensitive design (now CSS). Those principles include the importance of establishing multidisciplinary teams to plan projects; maintaining open, ongoing communication with stakeholders; and understanding the landscape, the neighboring community, and the area's valued resources before starting an engineering design.
CSS represents a departure from previous project development processes because it broadens the scope of considerations that factor into project decisions, going beyond just engineering principles and practices. As described by FHWA and AASHTO, CSS "is a collaborative, interdisciplinary approach that involves all stakeholders in providing a transportation facility that fits its setting. It is an approach that leads to preserving and enhancing scenic, aesthetic, historic, community, and environmental resources, while improving or maintaining safety, mobility, and infrastructure conditions."
Overcoming the Barriers
Rather than open the floodgates to CSS deployment, however, the legislative nudges toward increased flexibility and broader stakeholder involvement met with varying degrees of resistance. Being "flexible" was viewed as an unnecessary risk and one that added complexity, time, and effort to the process.
For DOT staffs accustomed to the traditional way of doing things, integrating CSS and adopting more flexible approaches may be challenging. For example, restrictive State design manuals might limit the range of solutions an engineer can consider for a project. Staffing also presents challenges when project managers lack experience managing complex projects involving multiple technical disciplines and external stakeholders.
States, however, are finding ways to overcome these challenges. Missouri, for example, purposefully wrote its new project implementation manual, Practical Design, "to allow flexibility for project- specific locations." In the manual's introduction, the Missouri DOT writes: "To accomplish Practical Design, we must properly define the scope by focusing on achieving the project purpose and need while considering the surroundings of each project. We must be sensitive to where the project is located, whether it is an interstate or a letter route. The surrounding context helps determine the design criteria." (See "Practical Design" by Joseph Jones on page 42.)
In 2006, Massachusetts also updated its highway design guidelines to provide designers and decisionmakers with a framework for incorporating context sensitive design and multimodal elements into transportation improvement projects. In fact, context sensitive design is one of three guiding principles for the new design guide, along with multimodal consideration and a clear project development process.
In a letter at the beginning of the Massachusetts Highway Department's (MassHighway) Project Development & Design Guide, Commissioner Luisa M. Paiewonsky wrote that one of the key features of the new guidebook is flexibility. "The new guidebook has significantly more flexibility in design requirements, particularly for lane and shoulder widths," she wrote.
Community context was also a major focus: "Recognizing that we live in a State full of classic New England downtowns, stone walls, historic districts, and natural resources, the new guidebook places much more emphasis on what the community looks like beyond the paved roadway. This approach will ensure that the roads we design are compatible with community surroundings."
Since MassHighway's publication of the new design guide, CSS thinking has become more engrained in the department's operations. "Little things have become routine," says Thomas A. DiPaolo, assistant chief engineer with MassHighway. "We now have project delivery teams, where it's routine for a project manager to have regular meetings with six or seven people representing the environmental division, traffic operations, the district office, the bridge section, the design consultant, and the town to ensure that everyone is on the same page. It sounds simple, but it wasn't routine to do this in the past."
Design and Risk Management
Transportation engineers and designers are trained to use accepted design criteria throughout project development. Striving to meet those criteria is the primary means by which high-quality roadways are produced. A highway or roadway that reflects full compliance with accepted design criteria decreases the probability that safety or traffic operational problems will develop. Therefore, using design values that lie within typical ranges provides a degree of quality control and a level of risk that transportation agencies consider acceptable.
According to the Project Management Institute, risk is defined as an uncertain event or condition that, if it occurs, has a positive or negative effect on a project's objectives. In other words, risk is a probability, not a certainty, and the level of consequences, positive or negative, are unknown.
Risks can sometimes yield rewards. That is, a risk could bring about a benefit that would be unachievable without taking that risk. Or a risk might be more tolerable when it is low relative to the potential benefit of the action incurring the risk. The key is to understand and evaluate potential risks associated with a project and weigh the pros and cons to make the best decisions possible.
In an ideal world, agencies would reduce or mitigate all potential risks associated with a project. But in the real world, limited budgets coupled with increased demands on agency staffs necessitate prioritizing where resources will be concentrated. Risk management is the process of identifying, evaluating, prioritizing, and mitigating risks, which guides a coordinated approach to minimize, monitor, and control those risks and their impacts. Part of this process is assessing the probability with which certain risks might occur. To the extent possible, risks should be quantified, both on the basis of their probability and their potential consequences.
Risk management starts early in the project design with identification of the range of potential risks and then selecting the most critical ones to mitigate or plan for. The process continues throughout the project design and requires knowledge of the project-specific risk factors and the exercise of sound professional judgment.
Identifying risks involves analysis of all pertinent issues. Knowledge of a project's geographic, environmental, safety, and traffic conditions and the assumptions underlying the design standards is essential to understanding the risks associated with selecting and applying those standards. Knowledge of human factors--how drivers interact with their vehicles and the road--can help identify potential flaws in the design that might not be readily apparent in the engineering drawings. In many cases, the risks associated with a decision can be mitigated with inclusion or enhancement of other features that could offset the risk.
For example, making optimum use of a constrained roadway right-of-way can be particularly challenging. What if full, standard lane and shoulder widths cannot be achieved? The Iowa DOT wrestled with this issue during reconstruction of a portion of I-235 in Des Moines. About 4.6 miles (7.4 kilometers) of the existing corridor was significantly narrower than the rest of the corridor.
Within this constrained area, providing a cross section that fully met design criteria would have significantly increased the costs and impacts of the project on adjacent land uses. The cross section that eventually was selected narrowed the two inside travel lanes on both sides by 6 inches (15 centimeters). This provided enough space to widen both inside shoulders by 1 foot (0.3 meter). The resulting design represented a compromise in both the lane width and shoulder width values. The consensus was that although this design did not meet the adopted design criteria, it would function well operationally and would most effectively use the available cross-sectional width to optimize safety.
During a recent roundtable session, sponsored by the Institute of Transportation Engineers, on agency challenges to integrating CSS, one participant noted that, to some, embracing CSS might seem equivalent to taking on more risk. But why not reframe the discussion, the participant said, to look at CSS in terms of a risk management strategy? What is the actual risk of making design modifications versus the risk of being unable to make any transportation improvement at all due to controversy or local opposition?
In fact, risk management and the application of CSS mirror one another. Both involve gathering information from a number of sources, evaluating and prioritizing that information, collaborating with stakeholders, and arriving at a course of action that makes the most sense for the unique circumstances at hand. Using both approaches can prove mutually beneficial, balancing a sensible project solution with an acceptable level of risk.
Designing for Safety
Highway planners and engineers need to be cognizant of two fundamental types of risk: risk of lawsuits arising from crashes allegedly associated with a design (tort risk) and risk of the solution not performing as expected in terms of safety, serviceability, and operations (engineering risk). Other risks associated with highway projects include delay, cost, political factors, differing site conditions, weather-related risks, and availability of materials.
Tort liability is a key risk. In the safety arena, engineers might be reluctant to consider design exceptions for fear of increasing an agency's vulnerability to tort litigation. A design exception, or waiver, allows for use of criteria lower than those specified as the minimum acceptable.
As noted in AASHTO's 2004 A Guide for Achieving Flexibility in Highway Design, if a design exception makes the most sense for a project given its context, and as long as granting the exception would not compromise the project's safety, the design exception process is a legitimate exercise of professional judgment, not evidence of a flawed design. If a design team works closely with stakeholders, is creative within the bounds of good engineering practice, and fully documents all decisions, it will have gone a long way toward minimizing the risk associated with a future tort action.
However, the application of more flexibility in design does not usually require consideration of a design exception. Often, engineers can choose appropriate design values from within the allowable range defined by the applicable design criteria. In fact, according to NCHRP Synthesis Report 316 Design Exception Practices, only 20 percent of State DOTs indicated that the advent of context sensitive design (now CSS) had increased the number of design exceptions they prepare. Almost all the respondents said their agencies view design exceptions as a value-adding process. Simply having a record of the decision process and its use in managing tort risk were cited as principal benefits.
With respect to risk, one might further classify safety as either nominal or substantive. Nominal safety refers to a design's adherence to design criteria or standards; substantive safety refers to the actual performance of a highway or facility as measured by the number of crashes per mile per year and the consequences of those crashes as specified by injuries, fatalities, or property damage.
Designing for safety is an exercise in risk management because the safety performance of any given project design is relative. It is not uncommon to have a road that is nominally safe--that is, all its geometric features meet design criteria--but substantively unsafe, having a known or demonstrated crash problem. Similarly, roads that are nominally unsafe (having one or more design features that do not meet current design criteria) can be substantively safe.
"There is a common misperception that incorporating flexibility into development for a road project means that the project's safety will be compromised," says Dwight Horne, FHWA's director of program administration. "This line of thinking does not fully consider how flexibility may actually enhance the safety of transportation projects."
The Hawaii State legislature went so far as to include explicit language in State law about the relationship of flexible design and safety. "The legislature expressly finds that flexible designs are not themselves less safe than earlier engineering practices. Rather, flexible design is simply part of the ongoing evolution within engineering that takes a broader range of considerations into account than may have been done in the past. Flexible design is not inherently less safe than some different or prior design; flexible design is a different and broader combination of factors to be considered in being safe."
In fact, says Horne, CSS and safety concerns are not only highly compatible, but applying CSS principles "goes one step beyond merely addressing safety by actually incorporating safety objectives into project development. Safety is actually a cornerstone of CSS."
One of the most frequent challenges for design practitioners is how to address the public's desire for trees within a highway right-of-way while minimizing the risk of the trees being struck by run-off-the-road vehicles. The Maryland SHA employed a creative solution to this challenge during reconstruction of State Route 355 in Montgomery County. Specifically, the agency used a nontraditional design to accommodate the retention of a prominent mature oak tree. Original plans for the widening showed the tree needed to be taken down; however, SHA staff reviewed the alignment and cross section, inspected the tree and surrounding area, and committed to preserving the tree through redesign.
The cross section and horizontal alignment were adjusted to place the tree in the median of State Route 355. The designers raised the profile of one direction of travel to create space for the tree's root system and designed a special irrigation and monitoring system. SHA used steel-backed, timber-faced guardrail (meeting the crash testing requirements of NCHRP Report 350 Recommended Procedures for the Safety Performance Evaluation of Highway Features) to shield the tree while improving safety for motorists.
Many CSS success stories are characterized by a high degree of stakeholder and community involvement, which provides a forum for discussing safety concerns. As stated in FHWA's Flexibility in Highway Design, "Having a process that is open, includes public involvement, and fosters creative thinking is an essential part of achieving good design.by identifying some possible approaches that fully consider aesthetic, historic, and scenic values, along with safety and mobility."
By involving stakeholders and the public early in the process, safety concerns associated with a project can be placed on the table, where project planners can discuss and address them, leading to improved safety further down the line in project development, and ultimately, a safer highway facility. Plus, employing the CSS approach could help reduce the risk of costly redesigns later in the process to address community concerns.
Flexibility in Design Speeds
AASHTO's A Guide for Achieving Flexibility in Highway Design stresses the need for knowledgeable, experienced highway engineers if the execution of a context sensitive project is to be successful. Flexible thinking is about making informed choices. Simple, rote application of the highest or lowest value within a range of design values without explicit consideration of context might not always lead to the most informed choices that best meet a project's objectives.
For example, selecting a design speed is one of the most critical choices a design professional makes. This decision establishes an index value that profoundly influences the design values for other road features, such as the sharpness of curves, the steepness of grades, and the footprint of the highway.
Some designers might interpret a lesser value for design speed as tantamount to choosing an inferior design. Or they might feel compelled by agency policies or guidelines to choose the highest value. But choosing the highest design speed imposes more stringent values for the alignment and cross section, which might in turn result in higher project costs or untenable environmental impacts.
Much like a master chef who grasps the nuances of how various ingredients combine in a recipe, a highway design professional needs to understand the functional basis of the components of a roadway and how they interact, including design speed, lane width, cross section, and alignment. Using this understanding, plus familiarity with the community context, the designer needs to judge whether a so-called substandard design element poses an acceptable risk. That is, the designer needs to decide whether the design's operational performance, safety, serviceability, or aesthetic character will be adversely affected.
MassHighway's new design guidebook expands the flexibility afforded designers in the selection of design speeds. The guidebook encourages engineers to consider the roadway context, implications for the safety and comfort of pedestrians and bicyclists, and implications for regional mobility. Specifically, flexibility is provided to allow design speeds that are lower, the same, or higher than existing operating speeds, depending on the project's purpose.
DiPaolo, from MassHighway, says the flexibility has always been there. "We've always made and documented design exceptions. The flexibility in the new guidebook has made it easier for designers to select appropriate values for each project and will likely lead to fewer design exceptions in the future."
Training and Outreach
As anyone who has ever engaged in stretching exercises to improve physical fitness can attest, exercising flexibility without knowing how to do so properly can be dangerous. Done right, you feel better. Done wrong, you could get hurt. Exercising flexibility in highway design is really no different.
AASHTO's A Guide for Achieving Flexibility in Highway Design stresses the importance of having skilled professionals: "The ability to develop a context sensitive solution by working within and sometimes outside design criteria, while maintaining the safety and operational integrity of the highway, requires a broad and deep understanding of the operational effects of highway geometry. For this reason, knowledgeable, experienced, professional highway engineers are essential for a successful context sensitive project."
To fill knowledge gaps and help engineers and designers gain confidence in applying flexibility and CSS principles, FHWA and its partners have sponsored numerous workshops, forums, and peer exchanges over the past decade. For example, in 2006, the American Society of Civil Engineers held a conference in Atlanta, GA, called Context Sensitive Solutions in Practice: What You Need to Know. And in February 2009, the Center for Transportation Studies at the University of Minnesota held a forum called Flexible Design for 21st Century Challenges: Balancing Competing Objectives and Optimizing Return on Investments.
Formalized training too is helping transportation professionals learn these approaches. FHWA's Resource Center has developed a workshop--Introduction to Human Factors Considerations in Highway Design--that provides insights on road user capabilities and behaviors and how these human factors can best be addressed in highway design decisionmaking.
Training in road safety audits (RSAs), such as the National Highway Institute (NHI) course Road Safety Audits/Assessments (FHWA-NHI-380069), has helped raise awareness and use of this proactive safety analysis method. RSAs, like CSS, rely on a multidisciplinary, collaborative approach to problem solving.
NHI also offers training courses that share a common theme of "safety effects," exploring safety performance functions and crash reduction factors, both of which help quantify the likely safety implications of a design alternative or a safety treatment. These courses include Safety and Operational Effects of Geometric Design Features (FHWA-NHI-380070), Application of Crash Reduction Factors (FHWA-NHI-380093), and Science of Crash Reduction Factors (FHWA-NHI-380094).
And, most recently, FHWA unveiled a 2-day NHI course, Highway Design: Applying Flexibility and Risk Management (FHWA-NHI-380095), focused on the core philosophy that good design requires more than simply applying standards. The course provides participants with knowledge to make informed decisions when applying engineering judgment and risk management in highway design. Exercises and case studies provide practical applications of current knowledge from research and operational experience of human factors and safety effects.
TRB too is promoting the benefits of design flexibility through a task force focused on CSS research and development. "We plan to put a greater emphasis on the concepts of practical design and practical solutions that have been developed recently due to the economic constraints that most State DOTs are facing," says Nick Stamatiadis, professor of civil engineering and transportation at the University of Kentucky and chairman of the TRB Task Force on Context Sensitive Design/Solutions.
Partnering for Livability
CSS and design flexibility are critical tools that can help DOTs contribute to creating more livable communities. FHWA defines "livable communities" as "places where the young and old can walk, bike, and play together; where historic neighborhoods are preserved; where farms, forests, and other green spaces are protected; where parents spend less time in traffic and more time with their children, spouses, and neighbors; where older neighborhoods can thrive once again. A livable community has safe streets, good schools, and public and private spaces that help foster a spirit of community."
U.S. Transportation Secretary Ray LaHood, at his Senate confirmation hearing, identified community livability as a top priority. He vowed to invest in infrastructure in a way that "recognizes the unique character of each community."
Toward that end, in June 2009, Secretary LaHood entered the U.S. Department of Transportation (USDOT) into a partnership with the U.S. Department of Housing and Urban Development and the U.S. Environmental Protection Agency to implement six livability principles that the three agencies will use to coordinate Federal investments in transportation, housing, and environmental protection. (See "Livability Principles" above.)
The new partnership aims to help U.S. families in all communities--rural, suburban, and urban--gain better access to affordable housing, more transportation options, and lower transportation costs. The three agencies will work together to ensure that these housing and transportation goals are met while simultaneously protecting the environment, promoting equitable development, and helping to address the challenges of climate change.
From the individual design engineer to entire DOT cultures, learning to embrace design flexibility and apply CSS approaches in projects ultimately will lead to improved community livability. As Secretary LaHood said at his confirmation hearing, "The era of one-size-fits-all transportation projects must give way to one where preserving and enhancing unique community characteristics, be they rural or urban, is a primary mission of our work rather than an afterthought."
Keith J. Harrison, P.E., is a safety/geometric design engineer in the FHWA Resource Center in San Francisco. He earned a B.S. in civil engineering at Worcester Polytechnic Institute and an M.S. in transportation planning and engineering at Polytechnic Institute of New York (now New York University). He is a member of the TRB Joint Task Force on Context Sensitive Design/Context Sensitive Solutions and secretary of the AASHTO Technical Committee on Environmental Design. Harrison has more than 30 years of experience helping FHWA partners achieve CSS.
Stephanie Roth, AICP, is a communications specialist with the FHWA Resource Center in Arlington, VA. She earned a B.A. from the University of Pittsburgh in political science and Spanish, and an M.S. in community and regional planning from the University of Texas at Austin. She is a member of the American Institute of Certified Planners. Roth has 16 years of experience in transportation planning and communications, working at the local, State, and Federal levels.
To schedule a session of the NHI course Highway Design:Applying Flexibility and Risk Management (FHWA-NHI-380095), visit www.nhi.fhwa.dot.gov. For more information, visit www.fhwa.dot.gov/environment/flex/index.htm or contact Keith Harrison at 415-744-2657 or firstname.lastname@example.org, or Stephanie Roth at 703-235-0509 or email@example.com.
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