Abstract

When highway project designs depart from design values found in the Kentucky Transportation Cabinet (KYTC) Highway Design Manual and AASHTO’s A Policy on Geometric Design of Highways and Streets, project managers at the agency must obtain either a design exception or design variance. While designers are more comfortable with exceptions and variances than they were 10 or 20 years ago, some hesitancy remains, especially among the Cabinet’s consultants. Misperceptions about what exceptions or variances entail or about their performance may underlie this reluctance. Exceptions and variances are best conceptualized as formal justifications for design decisions. Project managers merely need to describe why a design does not adhere to published guidance and illustrate that safety and mobility performance are not significantly compromised — in every instance new designs offer improvement over existing conditions. The limited number of research studies on design exceptions have found no evidence to suggest facilities where exceptions have been used have worse safety performance than those which abide by typical design values. To encourage project managers and designers to embrace cost-effective, context-adapted designs — and the role of variances and exceptions play in delivering those solutions — this report presents design axioms and case studies that document projects on which exceptions and variances have been used with success. Most of the exceptions and variances used on these projects are minor (e.g., narrowing shoulders, reducing design speeds), were critical for addressing the stated purposes and needs, and resulted in a solution that blended improved roadway with the surrounding contexts. Addition examples of mostly Highway Safety Improvement Program (HSIP) projects are catalogued that illustrate how creative fixes can be used to mitigate safety concerns.

Report Date

11-2021

Report Number

KTC-21-29/SPR19-575-1F

Digital Object Identifier

https://doi.org/10.13023/ktc.rr.2021.29

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