2.4 Performance Based Practical Design
2.4.1 What is Performance Based Practical Design?
What is PBPD? | |
What PBPD is: | What PBPD is not: |
Grounded in performance management | New regulation or requirement by FHWA |
Exercises engineering judgement to address a project’s purpose and need | New version of Value Engineering (VE) |
Uses appropriate performance-analysis tools | Replacement for Context Sensitive Solutions (CSS) |
Considers both short- and long-term project and system goals | Opportunity to disregard long-term needs |
- | Compromise on safety or user needs to save money |
Performance Based Practical Design (PBPD) is the process of performance evaluations, as previously discussed in
, during project development to guide alternative selections and, ultimately, geometric design decisions. PBPD modifies the traditional dimensional design approach to a “design up” approach – using engineering judgement and practical design to build up the improvements from the existing conditions to meet both project and system objectives.
PBPD is an approach to decision-making that encourages engineered solutions rather than reliance on maximum values or limits found in design manuals. PBPD is making practical decisions but making sure those decisions are based on an objective analysis of the relevant data.
FHWA discusses notable attributes of PBPD to be:
- PBPD focuses on performance improvements that benefit both project and system needs.
- Agencies make sound decisions based upon performance analysis.
- By scrutinizing each element of a project’s scope relative to value, need and urgency, a PBPD approach seeks a greater return on infrastructure investments.
PBPD Used In All Phases Of The Project Lifecycle | |
Planning | Preliminary Engineering & Design |
Define system and project purpose and need | Start with existing conditions as the baseline |
Develop concise project objectives from the purpose and need | Engineer solutions that meet the purpose and need – not just meet standards |
Consider project in the context of the system | Evaluate tradeoffs based on objective analysis of data |
Address all users | Support with design exceptions if needed |
- PBPD strengthens the emphasis on planning-level corridor or system performance needs and objectives when planning, scoping, and developing individual projects.
- PBPD can be implemented within the Federal-aid Highway Program regulatory environment utilizing existing flexibility.
- PBPD does not eliminate, modify, or compromise existing design standards or regulatory requirements.
- PBPD should consider multiple design and operating solutions to find the combinations that best addresses the project objectives.
Additional guidance on PBPD and Benefit/Costs Analyses can be found in the
. Examples of PBPD can also be found in the following references:
- FHWA PBPD case studies;
- Demonstrating Performance-Based Practical Design through Regional Performance-Based Planning – Federal Highway Administration (FHWA);
- Demonstrating Performance-Based Practical Design through Alternative Intersections – Federal Highway Administration (FHWA);
- Demonstrating Performance-Based Practical Design through Analysis of High-Occupancy Toll Lanes – Federal Highway Administration (FHWA); and
- FHWA-HIF-16-030 - Federal Highway Administration (FHWA).
2.4.2 Performance Based Practical Design Application
A PBPD approach should be utilized in all projects commensurate with the scope of the project. For 4R projects, the PBPD process can be used to optimize the design elements of a project that will provide the most safety at a better cost. The respective benefit-cost evaluation may use the tools and methods as described in the
, or other available approved tools. The level of analysis should be commensurate with the size and scope of the project. These tools will use a present-day cost and value of benefits to develop a Benefit/Cost ratio (including safety benefits). Generally, B/C ratios of 2.0 or higher represent a significant benefit, while ratios between 2.0 and 1.0, though considered positive, require additional sensitivity analyses to determine whether the identified upgrades are sufficiently beneficial for the project and TxDOT. B/C values below 1.0 should generally not be considered. For those elements that it is determined from a Benefit-Costs standpoint that the design minimums for a particular element will not be achieved. The PBPD analysis would serve as the basis for any needed design exceptions or design waivers.
Design guidelines for 3R projects have been developed to allow for greater design flexibility. 3R design decisions should be based on an assessment of the safety and traffic operational performance of the existing road and the cost-effectiveness of potential design improvements.
covers the application of PBPD for 3R projects and uses as the primary basis
, and
which has spreadsheet tools for comparing several alternatives or combinations of alternatives. There are additional tools and methodologies as referenced in the
. As with 4R projects, the Benefit-Costs analyses would serve as the basis for any needed design exceptions or design waivers.
also covers roadway tradeoff cross-section optimization guidance for 4 lane and 2 lane roadways (a form of PBPD) that may be applicable to certain 4R projects as well.
The TxDOT Safer by Design Tools (found on the
on TxDOT.gov), required for all applicable construction projects, is an additional tool available which utilizes proven safety measures based on the predictive method included in the
. This tool is unique to Texas roadway facilities and provides quantitative scores specific to how a change in a roadway design may directly influence the safety performance of a roadway.
2.4.3 What is the Difference between PBPD and Value Engineering?
FHWA views PBPD as the next step in the evolution of project development and design decision-making. Practical Design, Context Sensitive Solutions, Value Engineering and other similar initiatives and strategies are considered key components of a successful PBPD program.
Value Engineering:
- Method to determine the most cost-effective way to achieve proposed improvements;
- Typically focuses on maximizing project improvements; and
- Performed by multidisciplinary team not involved in the project.
PBPD:
- Method to determine the most cost-effective way to achieve the project objectives;
- Focuses on maximizing roadway system improvements, system safety, and TxDOT’s strategic goals; and
- Performed by project team and project stakeholders.