"Only 20% of [State Transportation Agencies] STAs indicated that the advent of context-sensitive design has increased the number of design exceptions they prepare ... Almost all STAs view design exceptions as a value-adding process. Simply having a record of the decision process and its use in managing tort risk are the principle benefits cited by STAs..."

SUMMARY

Nearly all highway and street construction and improvement projects are designed to conform to agency-adopted geometric design criteria. In some situations, achieving conformance with all design criteria is not practical or reasonable. A "design exception" is the process and associated documentation of creating or perpetuating a geometric feature that does not meet applicable criteria. Because design features that do not meet criteria may affect the safety and operational efficiency of the facility, a decision to depart from criteria should be deliberative, documented, and approved by an authorized official. All state transportation agencies (STAs) prepare design exceptions. However, the volume of design exceptions, project conditions requiring their preparation, technical processes employed, and approval roles vary substantially among states. Although cognizant of the benefits associated with preparing design exceptions, some states are concerned about the level of resources (i.e., agency personnel, funds, and time) used in the process. This report describes the range of design exception practices among STAs and the problems and suggested improvements based on the experience of state agency personnel...

BACKGROUND

All state transportation agencies (STAs) routinely develop designs and prepare plans for highway and street construction projects. Each STA is guided by a collection of design standards and policies, the purpose of which is to provide a safe, operationally efficient, and economical facility. For various reasons, it is not always practical or desirable that a project meets each and every design criteria and standard. For example, a design that meets all criteria may be extraordinarily expensive or impose severe community impacts. The decision to deviate from an applicable criterion is referred to as a design exception. Before making such a decision, design alternatives and their associated ramifications are evaluated through a deliberative process. The possible safety consequences of design exceptions are a concern to many designers. A study was conducted of design exceptions that were approved for projects on existing roadways in Kentucky. The analysis showed that crash rates at the project locations after construction were not higher than before construction.

In the United States, many road and street design practices have a connection to the federal-aid highway pro-gram, which is a partnership between the STAs and the FHWA. Under this program, federal funds are apportioned to each state for eligible activities (e.g., engineering and construction) subject to compliance with certain federal policies, one of which relates to design exceptions. The FHWA provides both regulatory (compulsory) and non-regulatory direction on design exceptions. This information can be found in the Federal-Aid Policy Guide, the relevant section of which is included as Appendix A of this synthesis. Under this regulation, a project that does not conform to applicable criteria may be approved when war-ranted. This is patently reasonable but very general; the nonregulatory supplement provides additional definition in several areas. The FHWA has established minimum design criteria for projects on the National Highway System (NHS), which includes the entire Interstate system. These criteria are included in A Policy on Geometric Design of Highways and Streets ("Green Book"). The Interstate system has several additional design criteria, which are included in A Policy on Design Standards-Interstate System. As noted in the next paragraph, there are certain exceptions to the applicability of these criteria. The Green Book provides criteria, guidance, and discussion on many design related topics, not all of which are equally critical. In the nonregulatory supplement of the Federal-Aid Policy Guide, the FHWA indicates that "[a]lthough all exceptions from accepted standards and policies should be justified and documented in some manner, the FHWA has established 13 controlling criteria requiring formal approval." Through this regulation and guidance, the FHWA has established certain requirements with respect to design policy and design exceptions; however, their scope and applicability are limited. As outlined in subsequent paragraphs, STAs hold considerable discretion on these matters as well.

Individual states may develop design standards and secure FHWA approval for nonfreeway NHS 3R (resurfacing, restoration, and rehabilitation) projects (see the Terminology section of this chapter for further information). Upon approval, these standards may be used in lieu of Green Book criteria on applicable projects. For preventive maintenance projects, the FHWA does not require design exceptions for retention of existing features that do not conform to current criteria. Design criteria for non-NHS facilities are established solely by STAs. A STA may adopt design criteria that are equal, lower, or higher than those in the Green Book for federal-aid, non-NHS projects. The decision to deviate from these non-NHS criteria is also a matter of STA discretion. States decide how to handle policy deviations that are not among the 13 controlling criteria and whether or not to develop 3R standards. STAs also set design policy and design exception procedures for non-NHS facilities.

Each STA has a unique operating environment. The prevailing conditions within individual states and the latitude that exists under the federal-aid program have led to considerable variation in the volume of design exceptions processed by states, the methods employed, and the level of detail provided in agency procedures. For example, several STAs estimated that on average they prepare one or two design exceptions annually; the California Department of Transportation (Caltrans) estimated its annual number at 500. Several states include their entire design exception guidance in 4 or 5 pages, whereas the New Jersey Department of Transportation (DOT) draft Design Exception Procedures Manual is 46 pages plus 38 pages of appendices.

External Links:

More Information: gulliver.trb.org/publications/nchrp/nchrp_syn316.pdf

Further Reading:

Design Exception Practices: A Synthesis of Highway Practice