2.4.1. Incorporating Flexibility and Creativity in Design

 “It is better to know some of the questions than all of the answers.” 

James Thurber

 

From an engineering design perspective, there are important considerations in developing alternatives that will lend themselves to context-sensitive solutions. These include the flexible application of established design criteria and guidelines and the use of design innovations to incorporate community needs and enhancements. Every deviation from design standards must consider the potential impacts on operations, safety, regional needs, and the surrounding environment and may result in a design exception or variance.   Design exceptions or variances must be requested from the GDOT Chief Engineer. Refer to Chapter 8 of the GDOT Plan Development Process.  Some potential CSD issues relating to design exceptions or variances include:

• Landscaped medians and oversized rights-of-way
• Canopy trees, historic trees, and clear zone policy to preserve them
• Special finish guardrails to minimize obstruction
• Reduced clear zone behind curb and gutter in constrained areas
• Inclusion of sidewalks and bike lanes as part of mitigations/alternatives
• Construction materials that blend with the environment
• Gateways, amenity corridors, and historic areas
• Neighborhood buffers, open space and trails as buffers
• Scenic view sheds and tourism, gathering, and events
• Budget and local funding to help pay for right-of-way / amenities (e.g. SPLOST)

 

It is important for GDOT design engineers that are part of a multi-disciplinary CSS project team to realize that the design criteria provided in the AASHTO Green Book, A Policy on the Geometric Design of Highways and Streets, or other criteria were intended to be flexible.  As stated in the Green Book’s Forward,

 

“The intent of this policy is to provide guidance to the designer by referencing a recommended range of values for critical dimensions. It is not intended to be a detailed design manual that could supersede the need for the application of sound principles by the knowledgeable design professional.  Sufficient flexibility is permitted to encourage independent designs tailored to particular situations.  Minimum values are either given or implied by the lower value in a given range of values.  The larger values within the ranges will normally be used where the social, economic, and environmental (SEE) impacts are not critical.”

(AASHTO, 2004)

 

The Green Book is applicable over a wide range of conditions and encourages designers to be flexible, to develop alternatives that fit particular situations, to be sensitive to environment, and recognize that the design concepts presented are for guidance. 

 

Creativity or flexibility in design does not involve ignoring design criteria or an agency’s accepted design practices.  Flexibility is achieved in consideration of all known factors and trade-offs.  The expected safety performance of a flexible solution should be consistent with the expectations provided by a full standard design.  Applying creativity is necessary to develop a unique solution to fit the needs to the project.  Per the AASHTO Green Book (Forward), “Unique combinations of design requirements that are often conflicting result in unique solutions to the design problems.”  Recognition and use of the flexibility inherent in design standards and the exercise of informed judgment by experienced personnel are important in the development of a CSS and responding to local topography and community character.

 

These three documents can assist in determining the design values suitable for a CSS:

• AASHTO Green Book - A Policy on the Geometric Design of Highways and Streets (AASHTO, 2004)  

• A Guide for Achieving Flexibility in Highway Design, 1st Edition (AASHTO, 2004)

• Flexibility in Highway Design (FHWA, 1997)

 

FHWA’s Flexibility in Highway Design shows how to make highway improvements while preserving and enhancing the adjacent land or community.  This document emphasizes the goal of a CSS, which is for project teams to design a roadway that fully considers the aesthetic, historic, and scenic values while meeting important safety and mobility goals.  Highway designers need to consider the impacts of not using the most conservative values specified in A Policy on the Geometric Design of Highways and Streets.

 

Context-sensitive design should result in a balance that reflects environmental concerns, community values, economic realities, and also what is needed to enhance safety, operations, and/or capacity.  A CSS project is in harmony with the community and environment in a number of ways. Consider the following:

• The visual impacts of the project on the environment and the community, and how the completed project will look from the perspective of the facility user, pedestrians, bicyclists, and others in community

• Aesthetic treatments that reflect the values and local flavor defined by stakeholders (e.g. indigenous landscaping)

• Land uses change over time, but the highway will outlast some of the land uses

• State roads serve as a network for safe, efficient time-sensitive transportation

• The design of community gateways or main streets can affect a community’s image

 

Some options that can be explored when incorporating flexibility in design and the selection of materials:

• Footprint: identify areas of consensus and conflict

• Materials: soften and enhance impact

• Streetscapes: add lighting, landscaping, furniture

• Civic need: promote and respect a sense of place

• Safety: provide the safest environment for all types of facility users (vehicular, pedestrian, bicycle)

Offering flexibility in the selection of materials is a good way to involve the public.  While cost will be a primary consideration, stakeholders appreciate being given the opportunity to voice their opinion, and can be give a range of feasible options from which to choose. Section 2.4.3. Considering Design Choices and Consequences offers further food for thought in terms of creative design options for CSD projects.