Diagnosis and Countermeasure Selection

Diagnosis of safety concerns at specific sites, whether those sites were identified by network screening or by other methods, is a process that is conducted manually by most highway agencies at present. An important step in diagnosis is the preparation of collision diagrams. Some agencies have automated the process of preparing collision diagrams for intersection locations; but in many agencies, the preparation of collision diagrams—as well as the rest of the diagnostic process—is conducted manually. A basic collision diagramming capability is included within SafetyAnalyst, but the Diagnosis Tool can also interface with selected commercially available collision diagramming software packages, including collision diagramming software with interactive capabilities.

The SafetyAnalyst software automates the preparation of collision diagrams, the identification of collision types that are overrepresented at specific locations, and the investigation of the specific accident patterns that are present. The software serves as an expert system to guide the user through office and field investigations of particular sites. For example, SafetyAnalyst generates a site-specific list of questions to be answered in a field visit to the site. The questions asked are determined based on the available data about the accident experience, geometric design, and traffic control at the site; the answers provide more detailed information on site conditions and field assessments of whether particular conditions are present. The answers to the field investigation questions posed by SafetyAnalyst are entered into the software and are used in identifying appropriate countermeasures for implementation to improve safety.

The selection of countermeasures for implementation is made by the user, not by the software. However, SafetyAnalyst assists users by suggesting for consideration a list of alternative countermeasures that are appropriate for the site-specific safety concerns. The logic that identifies appropriate countermeasures considers the accident patterns and related site conditions investigated in the diagnostic process. The user can then select one or more of the suggested countermeasures for further consideration or can add other countermeasures that they consider appropriate.

The automation of these traditionally manual procedures using an expert system approach provides a benefit to highway agencies by assuring that diagnosis and countermeasure selection activities are comprehensive and thorough. Suggestion of field investigation checklists and lists of candidate countermeasures by the software may help assure that all potentially effective countermeasures are considered. These activities have traditionally been conducted in highway agencies by very experienced engineers; however, many of those experienced engineers are retiring, and SafetyAnalyst may help their less-experienced successors conduct such studies.