2.3 Performance-Based Design Process

2.3.1 What is Performance-Based Design?

Performance-Based Design (PBD) is an evaluation of the performance impacts of highway design decisions. It provides an approach that looks at the outcomes of design decisions as the primary measure of design effectiveness. The
National Cooperative Highway Research Program (NCHRP) Reports 785 Performance-Based Analysis of Geometric Design of Highways and Streets and
839 A Performance-Based Highway Geometric Design Process
are publications that seek to guide project managers and designers through PBD processes.
  • Report 785
    establishes an approach designers can use to evaluate the performance trade-off of different project development and design decisions.
  • Report 839
    presents a revised geometric design process providing guidelines based on the project type and the problem or need being addressed.
These reports are recommended reading for all designers and project managers.

2.3.2 Performance-Based Design Guiding Principles

The principles that guide PBD allow designers to create usable, practical, and long-lasting highways and streets.
Intended Outcomes:
The foundational step in PBD is to determine and document a project’s purpose, need and problems. This is followed by establishing the desired project outcomes and goals.
Connection to Project Development Process:
Designers should consider the opportunities to apply performance-based analysis during each stage of project development (project initiation, planning, preliminary engineering, and final design). The ability to recognize the benefits of performance-based analysis is greater in the earlier stages of project development (planning and preliminary engineering), and harder to influence project outcomes during final design activities.
Performance Categories:
The goal of PBD is to focus on actual project performance instead of the traditional dimension-based design approach. Areas of performance characteristics include, but are not limited to:
  • Quality of service;
  • Safety;
  • Reliability;
  • Accessibility;
  • Infrastructure integrity;
  • Ease of use;
  • Ease of maintenance;
  • Visual quality; and
  • Fit to context and community.

2.3.3 Performance-Based Design Process

Figure 2-1
illustrates the steps in the general performance-based design process. Chapter 5 of
NCHRP Report 785
gives a detailed process framework for application of performance-based analysis. The application of the framework is organized into three broad project development phases – project initiation, planning, and preliminary engineering.
Project Initiation:
Project Context – Determine the context (rural, rural town, suburban, urban, or urban core) of the project to help identify the facility users and special needs influencing geometric design decisions. See
Chapter 3
for more discussion on context classification and its application.
Intended Outcomes – The results of determining the intended outcomes are the identification of the following:
  • Primary and supplementary target users of the project;
  • Project objectives and goals; and
  • Performance measures to evaluate progress toward the intended outcomes.
Planning:
Geometric Influences – This step identifies the geometric characteristics or decisions that influence a project’s performance as it relates to the categories of accessibility, mobility, quality of service, reliability, and safety.
Potential Solutions – Potential solutions should be developed with a particular awareness of what has been learned in previous steps. The solutions can be general concepts early in project development or more detailed, project specific solutions to address a specific need, issue, or challenge.
Preliminary Engineering:
Estimated Performance – Once the appropriate evaluation tool and resources are selected for the given project and performance measures, designers can apply the tool or resource to assess the project alternatives’ relative performance.
Financial Feasibility – Financial feasibility approaches include:
  • Total construction and maintenance cost of the alternative;
  • Cost effectiveness of the alternative; and
  • Benefit/cost ratio of the alternative.
Selection – Based on the results of the estimated performance and financial feasibility step, the designer will select a preferred alternative or refine alternatives and reevaluate their performance.
Performance-Based Design Process ( click in image to see full-size image)
Figure 2-1 Performance-Based Design Process

2.3.4 Resources for Performance Based Analysis

AASHTO’s Highway Safety Manual (HSM)
is the most prevalent resource for performance-based methodology. Other PBD resources have been developed and continue to be developed through research. Such resources include: