This information guide introduces users to design exceptions, which is a documented decision to design a section of highway or intersection to criteria that do not meet minimum values established for a project. The manual discusses a process for issuing design exceptions, including assessing and managing the risks associated with design exceptions. The tool also presents the 13 controlling criteria for geometric design that apply to the National Highway System (NHS) so users can reference the minimum allowed values. A formal design exception is required if these controlling criteria are not met for the NHS. Finally, the guide lists many potential mitigation strategies to counteract the negative risks associated with design exceptions (e.g., when proposing a design exception for stopping sight distance, designers could consider adding lighting or providing advance warning signs to assist drivers in a potentially unsafe area).
- Federal Highway Administration (FHWA)
This information guide is free of charge at the following link:
Mitigation Strategies for Design Exceptions