APWA Representation on the AASHTO Technical Committee on Geometric Design

Joe Kroboth, III, PE, LS, PWLF
APWA Representative to the TCD
Director, Transportation and Capital Infrastructure
Loudoun County, Virginia

With review and contributions by:

Marshall Elizer, PE
Assistant Secretary
Multimodal Development & Delivery
Washington State Dept. of Transportation

The American Public Works Association is afforded a rare opportunity to participate and provide representation on the American Association of State Highway and Transportation Officials (AASHTO), Technical Committee on Geometric Design (TCGD). This Committee is responsible for developing and updating several publications, like A Policy on Geometric Design of Highways and Streets, more commonly known as the AASHTO Green Book, and similar policy documents.

AASHTO, and its predecessor AASHO, have set the standard in highway design policy since the 1940s. The fundamental processes of highway and street design have remained essentially unchanged since its origin. During the past 75 years, transportation needs have evolved, and much has been learned about the relationships among geometric design, vehicle characteristics, human factors, safety, context, and operations.

The tide started to shift in 1998, when the Maryland State Highway Administration (SHA), in cooperation with AASHTO and the Federal Highway Administration (FHWA), hosted “Thinking Beyond the Pavement: A National Workshop on Integrating Highway Development with Communities and the Environment While Maintaining Safety and Performance.” That conference was soon followed by the development of the National Cooperative Highway Research Program’s (NCHRP) Research Report 480: A Guide to Best Practices for Achieving Context-Sensitive Solutions (2002), and then FHWA’s Guide for Achieving Flexibility in Highway Design (2004). These documents led to the creation of the Context Sensitive Solutions/Design (CSS/D) process that considers physical aspects or standard specifications of a transportation facility and the economic, social, and environmental resources in the community being served by that facility.

In 2014, NCHRP Research Report 785: Performance-Based Analysis of Geometric Design of Highways and Streets was released. Later in 2017, NCHRP released Research Report 839: A Performance-Based Highway Geometric Design Process. These documents send a message to the highway and street engineering industry: times are about to change. The old-fashioned approach to highway and street design has taught us to accept minimum design criteria to produce adequate performance and safety for the traveling public. Our highway and street design paradigm has been to meet these standards or criteria rather than to specifically provide sustainable traffic operations and safety (Neuman et al., 2017).

The TCGD embraces the notion of context-sensitive, multimodal, performance-based design and intends to integrate the concepts found in Research Report 785 and 839 and other modern engineering research into the eighth edition of the Green Book (GB8). Modern-day research findings suggest all geometric designs should be measured in the metrics of transportation performance, including mobility for all modes, accessibility, safety, maintenance, operations, and state of good repair. Research Report 839 suggests geometric design criteria for any given project should be established based on the context of the project location and not limited to the facility type. Maybe we should be asking ourselves, “What is the place-type where this roadway is located, and what are the appropriate characteristics of the roadway within this place?”

Performance-based design incorporates a design process that considers explicit consideration of performance measures, typically operational and safety performance measures. Each design decision should be explicitly assessed in terms of its potential impact on operations and safety (Neuman et al., 2017, p. 13). The companion report, NCHRP 785: Performance-Based Analysis of Geometric Design of Highway and Streets (Ray et al., 2014), provides a principals-focused approach that looks at the outcomes of design decisions as to the primary measure of design effectiveness. These research reports push highway designers to select performance measures that align with outcomes, evaluate the impact of alternative geometric design decisions on those performance measures, and arrive at solutions that achieve the overall desired project outcomes.

If you intend to be a highway and street design practitioner for several more years, do not wait any longer to get up to speed on the latest research in context-sensitive, multimodal, performance-based highway and street design decision-making.

References

Ray, B.L. et al. (2014). Research Report 785, Performance-based analysis of geometric design of Highways and streets. Found at: https://www.nap.edu/catalog/22285/performance-based-analysis-of-geometric-design-of-highways-and-streets. National Cooperative Highway Research Program. Transportation Research

Neuman, T.R. et al. (2002). Research Report 480, A guide to best practices for achieving context-sensitive solutions. Found at: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_480a.pdf. National Cooperative Highway Research Program. Transportation Research

Neuman, T.R. et al. (2017). Research Report 839, A performance-based geometric design process. Found at: https://www.nap.edu/catalog/24626/a-performance-based-highway-geometric-design-process. National Cooperative Highway Research Program. Transportation Research