A critical aspect of the design process is the process of considering and documenting the need for design exceptions.

Best Practices for Risk Management (1)

State laws regarding tort suits vary, but certain general best practices apply across most jurisdictions. First, stakeholders should recognize that transportation agencies limit greatly the risk of a successful tort suit involving a design issue by focusing on design solutions that are proven, i.e., that are within current design guidelines and criteria. Thus providing a nominally safe, i.e., within criteria, design is the first and major step toward minimizing tort risk.

Occasionally, however, situations arise in which an acceptable design cannot be achieved given the site-specific situation under the design criteria that were selected for the project. The judicious use of design exceptions (referred to by some as design deviations) may be acceptable if in the expert opinion of the highway professional the exception will not result in or produce a substantive safety problem.

The term design exception refers to acceptance of a design value outside that within the range considered acceptable for the conditions. Examples would include a narrower shoulder (say, 4-foot versus 10-foot), narrower lane width, sharper curve for a given design speed, etc.

Exhibit F-2 (CSD_152) summarizes the design features considered by the FHWA as requiring a design exception should their design dimension fall outside the normal design range. Individual states may generally follow FHWA practice, but it is common for states to include other design elements as part of their design policy for considering design exceptions. Appendix F also contains the design exceptions review form from the Federal Highway Administration, Federal Lands Highway Division, Design Standards Information.

Exhibit F-2 (CSD_152)
Controlling* Geometric Design Criteria
*Design elements considered by FHWA to be of sufficient importance to require a Design Exception Request if design criteria are not met.

A critical aspect of the design process, including design decision making and risk management, is the process of considering and documenting the need for design exceptions. In most cases, key senior staff within an agency such as the Chief Engineer or Roadway Design Engineer must review and approve design exceptions. Documentation of the need for an exception is critical to assure good decision making and as risk management. The design exception request includes the following:

* Description of existing highway conditions and proposed improvement project
* Thorough description of the substandard feature(s), providing specific data identifying the degree of deficiency
* Crash data for at least the latest 3-year period, indicating frequency, rate, and severity of crashes
* Costs and adverse impacts that would result from meeting current design standards
* Safety enhancements that will be made by the project to mitigate the effects of the substandard feature
* Discussion of the compatibility of the proposed improvement with adjacent roadway segments

A well-performed and documented design exception represents the best defense for an agency should a lawsuit occur as a consequence of a crash that occurred within the project at a later date. Appendix F contains examples of design exception reports from two states - two from Connecticut, and one from Iowa. The latter state employs a process in which quantitative safety analyses are part of the process. Designers are expected to estimate the substantive safety performance of the proposed design to support decision making.