SSAM 3.0 | NGSIM

Trajectory-Based Safety Assessment

SSAM 3.0 builds on the Federal Highway Administration's Surrogate Safety Assessment Model concept: automatically identifying, classifying, and evaluating traffic conflicts from vehicle trajectory data generated by microscopic traffic simulation models.

The FHWA SSAM overview describes surrogate safety analysis as a way to evaluate roadway safety before crashes occur, using trajectory data to estimate conflict frequency and severity. SSAM 3.0 extends this approach with improved performance, grade-separation support, 3D conflict visualization, and interfaces for simulation integration.

ETFOMM and SSAM Integration

ETFOMM differentiation: FHWA's SSAM software page identifies only two listed simulation platforms with z-coordinate trajectory support for differentiating at-grade and grade-separated conflicts: VISSIM 9 or later and ETFOMM Cloud Service. ETFOMM is also designed to interface directly with SSAM during simulation, supporting second-by-second safety analysis workflows.

ETFOMM's native connection to SSAM is important because it allows simulated vehicle movements, trajectories, and intersection geometry to flow directly into safety analysis. This reduces the friction between simulation and safety assessment and supports research workflows where operational performance and surrogate safety measures are evaluated together.

Key Capabilities

Conflict analysis

Trajectory Conflict Measures

Processes simulated trajectories to evaluate safety performance measures such as time-to-collision, post-encroachment time, speed, relative speed, and conflict location.

3D visualization

Grade-Separated Conflicts

Supports three-dimensional conflict mapping and z-coordinate trajectory logic to help distinguish at-grade conflicts from grade-separated movements at interchanges and complex facilities.

Performance

C++ and Parallel Computing

The FHWA TechBrief describes SSAM 3.0 enhancements including C++ reimplementation, OpenMP-based parallel computing, and substantial computation-time improvement over earlier Java-based versions.

Integration

ETFOMM Interface

Supports simulation-to-safety workflows where ETFOMM trajectory outputs and network geometry can be used directly in SSAM analysis and visualization.

Research Background

FHWA publication FHWA-HRT-17-027 describes the 2017 open source SSAM enhancement and update, including improved safety measures, 3D conflict graphics, advanced computing, C++ restructuring, parallel computing, ETFOMM integration, and API functions for simulation software interfaces.

Reference to FHWA documents is provided for technical and historical context. It does not imply FHWA endorsement of any commercial product, service, or manufacturer.