USA Banner
  U.S. flag
              An official website of the United States government Here's how you knowOfficial US Government Icon
              **Official websites use .gov**A **.gov** website belongs to an official government organization in the United States.
            Secure Site Icon
              **Secure .gov websites use HTTPS**
                  A **lock** ( A locked padlock ) or **https://** means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites. 
 U.S. Department of Transportation Icon United States Department of Transportation
 Search DOT
            Search
                    About FHWAFHWA Organization
                Headquarters Offices
                Field Offices
                Strategic Plan
                Business Opportunities
                Staff Directories
                Careers
                Highway History
                Contact UsProgramsAcquisition Management
                Civil Rights
                Federal Lands Highway
                Infrastructure
                Innovative Program Delivery
                Operations
                Planning, Environment, and Realty
                Policy
                Research, Development, and Technology
                Safety
                Browse by TopicsResourcesCore Highway Topics
                Federal Aid Essentials
                Automation
                Complete Streets
                Laws and Regulations
                Policy & Guidance Center
                Section 508
                Publications and Statistics
                Professional Development
                National Highway Institute
                Resource Center
                Accessibility Resource Library
                FHWA Research LibraryNewsroomPress Releases
                Speeches & Testimony
                Photos
                Videos
                Media ContactsMenu OFFICE OF RESEARCH, DEVELOPMENT, AND TECHNOLOGY AT THE TURNER-FAIRBANK HIGHWAY RESEARCH CENTER Home
                        Research
                        Turner-Fairbank Highway Research Center
                        Research and Development


            
            In This Section
        Explore Research and Technology
                Safety R&D Overview
                Safety Data and Analysis
                                Overview
                Development of Crash Modification Factors (DCMF) Program
                Evaluations of Low Cost Safety Improvements Pooled Fund Study (ELCSI–PFS)
                Surrogate Safety Assessment Model
                Human Factors
                Intersection Safety
                Motorcycle Safety
                Motorcycle Crash Causation Study
                Pedestrian and Bicycle Safety
                Roadway Safety
                                Overview
                Interactive Highway Safety Design Model
      
   Contact Us
      Turner-Fairbank Highway Research Center
      
                    
            United States Department of Transportation Federal Highway Administration6300 Georgetown PikeMcLean, VA 22101United States
      
          
    **Email:**TFHRC.webmaster@dot.gov
    If you are deaf, hard of hearing, or have a speech disability, please dial 7-1-1 to access telecommunications relay services.
                
                Surrogate Safety Assessment Model Overview
    

    
    
          **A simulation and analysis project with Federal Highway Administration (FHWA) to predict the safety of roadways before crashes occur.**

The Surrogate Safety Assessment Model (SSAM) is a software application developed to automatically identify, classify, and evaluate traffic conflicts in the vehicle trajectory data output from microscopic traffic simulation models. The SSAM also has built-in statistical analysis features for conflict frequency and severity measures that can aid analysts in the design of safe traffic facilities.

SSAM (version 2.16) was initially developed and released to the public in 2008 with additional enhancements completed in 2017. This latest 2017 release, SSAM (version 3.0), improves software performance and adds capability of differentiating between at grade and grade separated conflicts at interchanges.

**Description**

The safety of intersections, interchanges, and other traffic facilities is most often assessed by tracking and analyzing police-reported motor vehicle crashes over time. Given the infrequent and random nature of crashes, this process is slow to reveal the need for remediation of either the roadway design or the flow-control strategy. This process is also not applicable to assess the safety of new roadway designs that have yet to be built or new flow-control strategies that have yet to be applied in the field.

**This research was funded by the FHWA, and consists of two initial projects:**

Surrogate Safety Measures From Traffic Simulation Models, Publication Number: FHWA-RD-03-050.
	Surrogate Safety Assessment Model (SSAM) and Validation, Final Report: FHWA-HRT-08-051.Detail

A conflict is, simply put, a scenario where two road users will likely collide without evasive action. An example is illustrated in Figure 1, where a vehicle is angling across two lanes to the left turn bay and has abruptly cut in front of another vehicle that must decelerate to avoid a collision.

Traffic Studies
"Photo of a software illustrated vehicle collision scenario "Traffic conflicts have been studied since the late 1960s as a technique to assess the safety of a location, with the understanding that conflict frequency is correlated with the risk of actual collision.

Conflict scenario from SSAM application

Software Applications for Analysis

Conflict studies traditionally use personnel trained to identify and record conflicts observed at an intersection. In this research, the SSAM software application was developed to automate conflict analysis by directly processing vehicle trajectory data. Researchers specified an open-standard "universal" vehicle trajectory data format designed to provide the location and dimensions of each vehicle approximately every 10th of a second. It is hoped that video processing technology will, in the coming years, be capable of automatically extracting vehicle trajectory data adequate for SSAM processing.

Although, the trajectory file format was previously supported as an export option by four popular traffic microsimulation packages–AIMSUN, Paramics, TEXAS, and VISSIM–the differentiating of grade separated conflicts feature is available for 1) VISSIM 9 (and it's later release), and 2) ETFOMM (Enhanced Transportation Flow Open-Source Microscopic Model) Cloud Service) (ECS) because of the implementation of the “z-coordinate” in trajectory files by their software developers. It is also important to recognize that the SSAM software is mainly focused on conventional automobile type of safety conflict analysis while the VISSIM trajectory output files would contain all traffic (vehicles, pedestrians, buses, bicycles, etc.) in its trajectory output files.

Resources

The SSAM software is available freely to the public. Please reference to the “SSAM Software Download” section below in order to download the SSAM software installation program and its related documents.

**SSAM Software Download**

Please find SSAM software code (version 3.0) and program information here on GitHub. Please use Google Chrome if you do not have the latest version of Microsoft Edge.

Parties interested in downloading the SSAM software (version 3.0) are encouraged to carefully review the READMI.txt and documents in the “Documentation” folder prior to the installation of SSAM software. Please also be advised that FHWA is only distributing the SSAM software but does not provide any additional follow-up technical assistance.

This SSAM software tool and its related documents are disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this SSAM tool and its associated documents.
              **Project Contact**
Clayton Chen
clayton.chen@dot.gov
      
    
          Last updated: Tuesday, May 3, 2022 U.S. DEPARTMENT OF TRANSPORTATION

**Federal Highway Administration**

1200 NEW JERSEY AVENUE, SE

WASHINGTON, DC 20590

202-366-4000Subscribe to email updates
                    About
  

        
              About FHWA
                Careers
                Org Chart
                Staff Directories
                Work with UsPrograms
  

        
              Acquisition Management
                Civil Rights
                Federal Lands Highway
                Infrastructure
                Innovative Program Delivery
                Operations
                Planning, Environment, and Realty
                Policy
                Research, Development, and Technology
                SafetyPolicies, Rights, Legal
  

        
              About DOT
                Accessibility
                Budget and Performance
                Civil Rights
                FOIA
                Information Quality
                No FEAR Act
                Office of Inspector General
                Privacy Policy
                USA.gov
                Web Policies and Notices
                Web StandardsNews & Events
  

        
              Newsroom
                Press Releases
                Speeches & Testimony
                Media Contacts
                Connect with Us