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Flexibility in Highway Design

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Part I The Design Process

Part II Design Guidelines

Part III Case Studies


Letter from the Administrator

Dear Colleague:

One of the greatest challenges the highway community faces is providing safe, efficient transportation service that conserves, and even enhances the environmental, scenic, historic, and community resources that are so vital to our way of life. This guide will help you meet that challenge.

The Federal Highway Administration (FHWA) has been pleased to work with the American Association of State Highway and Transportation Officials and other interested groups, including the Bicycle Federation of America, the National Trust for Historic Preservation, and Scenic America, to develop this publication. It identifies and explains the opportunities, flexibilities, and constraints facing designers and design teams responsible for the development of transportation facilities.

This guide does not attempt to create new standards. Rather, the guide builds on the flexibility in current laws and regulations to explore opportunities to use flexible design as a tool to help sustain important community interests without compromising safety. To do so, this guide stresses the need to identify and discuss those flexibilities and to continue breaking down barriers that sometimes make it difficult for highway designers to be aware of local concerns of interested organizations and citizens.

The partnership formed to develop this guidance grew out of the designrelated provisions of the Intermodal Surface Transportation Efficiency Act of 1991 and the National Highway System Designation Act of 1995. Congress provided dramatic new flexibilities in funding, stressed the importance of preserving historic and scenic values, and provided for enhancing communities through transportation improvements. Additionally, Congress provided that for Federalaid projects not on the National Highway System, the States have the flexibility to develop and apply criteria they deem appropriate.

It is important, therefore, that we work with our State and local transportation colleagues to share ideas for proactive, community oriented designs for transportation facilities. In this guide, we encourage designers to become partners with transportation specialists, landscape architects, environmental specialists, and others who can bring their unique expertise to the important task of improving transportation decisionmaking and preserving the character of this Nation's communities. As illustrated in the guidance, we can encourage creativity, while achieving safety and efficiency, through the early identification of critical project issues, and through consideration of community concerns before major decisions severely limit design options.

We believe that design can and must play a major role in enhancing the quality of our journeys and of the communities traveled. This guide will help you achieve those dual purposes.

Sincerely yours,

Jane F. Garvey

Acting Federal Highway Administrator

Signature of Jane F. Garvey

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This Guide is about designing highways that incorporate community values and are safe, efficient, effective mechanisms for the movement of people and goods. It is written for highway engineers and project managers who want to learn more about the flexibility available to them when designing roads and illustrates successful approaches used in other highway projects. It can also be used by citizens who want to gain a better understanding of the highway design process.

Congress, in the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 and the National Highway System Designation (NHS) Act of 1995, maintained a strong national commitment to safety and mobility. Congress also made a commitment to preserving and protecting the environmental and cultural values affected by transportation facilities. The challenge to the highway design community is to find design solutions, as well as operational options, that result in full consideration of these sometimes conflicting objectives.

To help meet that challenge, this Guide has been prepared for the purpose of provoking innovative thinking for fully considering the scenic, historic, aesthetic, and other cultural values, along with the safety and mobility needs, of our highway transportation system. This Guide does not establish any new or different geometric design standards or criteria for highways and streets in scenic, historic, or otherwise environmentally or culturally sensitive areas, nor does it imply that safety and mobility are less important design considerations.

When Congress passed ISTEA in 1991, in addition to safety, it emphasized the importance of good design that is sensitive to its surrounding environment, especially in historic and scenic areas. Section 1016(a) of ISTEA states:

If a proposed project ...involves a historic facility or is located in an area of historic or scenic value, the Secretary may approve such project ...if such project is designed to standards that allow for the preservation of such historic or scenic value and such project is designed with mitigation measures to allow preservation of such value and ensure safe use of the facility.

Aesthetic, scenic, historic, and cultural resources and the physical characteristics of an area are always important factors because they help give a community its identity and sense of place and are a source of local pride.

In 1995, Congress reemphasized and strengthened this direction through the NHS Act, which states, in section 304:

A design for new construction, reconstruction, resurfacing... restoration, or rehabilitation of a highway on the National Highway System (other than a highway also on the Interstate System) may take into account...[in addition to safety, durability and economy of maintenance]...

  1. the constructed and natural environment of the area;
  2. the environmental, scenic, aesthetic, historic, community, and preservation impacts of the activity; and
  3. access for other modes of transportation.

The National Highway System (NHS) consists of approximately 161,000 miles of roads, including the Interstate System, or 4 percent of the total highway mileage. The primary purpose of the NHS is to ensure safe mobility and access. By emphasizing the importance of good design for these roads, Congress is saying that careful, contextsensitive design is a factor that should not be overlooked for any road.

A Policy on the Geometric Design of Highways and Streets (Green Book), published by the American Association of State Highway and Transportation Officials (AASHTO), contains the basic geometric design criteria that establish the physical features of a roadway. This Guide is correlated to a large extent to the Green Book because that is the primary geometric design tool used by the highway design community. Like the Green Book, this Guide contains sections on functional classification, design controls, horizontal and vertical alignment, crosssection elements, bridges, and intersections. There are many good projects highlighted in this Guide that were achieved working within the parameters of the Green Book to obtain safety and mobility and to preserve environmental and cultural resources. These projects used the flexibilities that are available within the criteria of the Green Book. These projects also used a comprehensive design process, involving the public and incorporating a multidisciplinary design approach early and throughout the process.

If highway designers are not aware of opportunities to use their creative abilities, the standard or conservative use of the Green Book criteria and related State standards, along with a lack of full consideration of community values, can cause a road to be out of context with its surroundings. It may also preclude designers from avoiding impacts on important natural and human resources.

This Guide encourages highway designers to expand their consideration in applying the Green Book criteria. It shows that having a process that is open, includes public involvement, and fosters creative thinking is an essential part of achieving good design. This Guide should be viewed as a useful tool to help highway designers, environmentalists, and the public move further along the path to sensitively designed highways and streets by identifying some possible approaches that fully consider aesthetic, historic, and scenic values, along with safety and mobility. It also recognizes that many designers have been sensitive to the protection of natural and humanmade resources prior to ISTEA.

The decision to use and apply the concepts illustrated and discussed in the Guide for any specific project remains solely with the appropriate State and/or local highway agencies. In addition, while many of the concepts discussed will clearly aid the decision process, it must be recognized that changes in the design or design criteria will not always resolve every issue to a mutual level of satisfaction.

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An important concept in highway design is that every project is unique. The setting and character of the area, the values of the community, the needs of the highway users, and the challenges and opportunities are unique factors that designers must consider with each highway project. Whether the design to be developed is for a modest safety improvement or 10 miles of newlocation rural freeway, there are no patented solutions. For each potential project, designers are faced with the task of balancing the need for the highway improvement with the need to safely integrate the design into the surrounding natural and human environments.

photo: street with cars parked on the right and a tree-lined grassy median on the left

In order to do this, designers need flexibility. There are a number of options available to State and local highway agency officials to aid in achieving a balanced road design and to resolve design issues. These include the following:

This Guide illustrates the flexibility already available to designers within adopted State standards. These standards, often based on the AASHTO Green Book, allow designers to tailor their designs to the particular situations encountered in each highway project. Often, these standards alone provide enough flexibility to achieve a harmonious design that both meets the objectives of the project and is sensitive to the surrounding environment.

When faced with extreme social, economic, or environmental consequences, it is sometimes necessary for designers to look beyond the "givens" of a highway project and consider other options. The design exception process is one such alternative. In other cases, it may be possible to reevaluate planning decisions or rethink the appropriate design.

For existing roads, sometimes the best option is to maintain the road as is or make only modest 3R improvements. Since the passage of ISTEA, States also have the ability to develop new standards outside the Green Book criteria for all roads not on the NHS. It is important, however, to recognize that the Green Book criteria are based on sound engineering and should be the primary source for design criteria. When the impact of the proposed action is evaluated and flexible design considerations are appropriate, they should be investigated.

All these options may give designers flexibility to use their expertise and judgment in designing roads that fit into the natural and human environments, while functioning efficiently and operating safely.

The ultimate decision on the use of existing flexibility rests with the State design team and project managers. Each situation must be evaluated to determine the possibilities that are appropriate for that particular project. Managers are encouraged to allow the designers to work with staff members from other disciplines to aid in exploring options, constraints, and flexibilities.

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Updated: 9/19/2012
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