Research & Data

Crash Injury Research

Mission

The Crash Injury Research and Engineering Network (CIREN) conducts in-depth investigations of real-world motor vehicle crashes to understand how specific crash, vehicle, and occupant factors contribute to injury outcomes. CIREN integrates prospective data collection with expert multidisciplinary analysis of medical and engineering evidence to determine injury causation in every investigated crash. The mission of CIREN is to improve the prevention, treatment, and rehabilitation of motor vehicle crash injuries—reducing deaths, disabilities, and their human and economic impact.

Background

CIREN was established following a 1985 National Academy of Sciences recommendation in Injury in America, which called for injury research through multidisciplinary collaboration among experts in engineering, medicine, and related fields. This collaborative approach remains the cornerstone of CIREN’s work. CIREN teams serve four key roles: 

  • Database – Systematic collection of over 1,000 data points per case covering crash environment, vehicle damage, restraint systems, post-crash medical care, case subject medical history, injury outcome, and treatment.
  • Sentinel – Early detection of environmental, technical, or human factors contributing to injury in motor vehicle crashes.
  • Knowledgebase – Comprehensive case reviews conducted by teams of engineers, medical professionals, epidemiologists, and crash investigators to assess injury causation and ensure data accuracy.
  • Research Catalyst – Generating research informed by real-world crash investigations and clinical experience, addressing current medical, technical, and socioeconomic challenges.

Methods

CIREN cases are identified, consented, and enrolled at five Medical Centers located within Level I trauma centers that treat large numbers of motor vehicle crash victims. With participant consent, CIREN obtains access to de-identified medical records and digital radiology data not available in any other NHTSA field crash investigation study. Medical center teams are led by experienced trauma surgeons and emergency physicians and include trained crash investigators and project coordinators. The crash investigators follow standardized NHTSA protocols to document crash circumstances and perform crash reconstructions. Medical personnel conduct extensive review of patient records and imaging to abstract a comprehensive report of injuries sustained for each case. The medical imaging is retained for research purposes. 

CIREN cases are analyzed by four Engineering Centers based at academic research institutions with extensive expertise in vehicle crash analysis and human injury biomechanics. Engineering teams are led by highly experienced mechanical engineers, typically specializing in biomechanics. Both medical and engineering teams are supported by multidisciplinary experts, including additional physicians, engineers, epidemiologists, nurses, and other research professionals who contribute to the comprehensive analysis of each case. 

Each CIREN case undergoes a structured, collaborative review involving the Medical Center, Engineering Center, Quality Control Center, and NHTSA personnel. Medical Centers present findings from vehicle and scene inspections, along with detailed medical and treatment data. Engineering Centers conduct the injury causation analysis, identifying contact locations, applied forces, and injury mechanisms. In some cases, computational reconstructions are used to enhance the injury causation assessment. The Quality Control Center performs a comprehensive, element-by-element review to ensure data completeness, accuracy, and adherence to protocol. NHTSA then conducts a final review before cases are published to the public case viewer and tabular files (see Data Access).

  • Emory University – Atlanta, GA (enrolling patients at Grady Memorial Hospital in Atlanta, GA)
  • Inova Trauma Center – Falls Church, VA (also enrolling patients at the University of Virginia Medical Center in Charlottesville, VA and Valley Health Winchester Medical Center in Winchester, VA)
  • University of Alabama at Birmingham – Birmingham, AL
  • University of Maryland R Adams Cowley Shock Trauma Center – Baltimore, MD
  • Wake Forest University – Winston-Salem, NC (enrolling patients at Atrium Health Wake Forest Baptist Medical Center in Winston-Salem, NC and Atrium Health Carolinas Medical Center in Charlotte, NC)
  • Emory University Department of Emergency Medicine – Atlanta, GA (in partnership with University of Michigan Transportation Research Institute – Ann Arbor, MI)
  • Medical College of Wisconsin Department of Neurosurgery – Milwaukee, WI
  • University of Virginia Center for Applied Biomechanics – Charlottesville, VA
  • Virginia Tech - Wake Forest University Center for Injury Biomechanics – Winston-Salem, NC
     
  • Crash Research and Analysis, Inc. – Elma, NY
  • Children’s Hospital of Philadelphia (2005-2010)
  • Children’s National Medical Center (1997-2005)
  • County of San Diego (1997-2010)
  • University of Medicine and Dentistry of New Jersey (1997-2005)
  • University of Miami Jackson Memorial Hospital (1997-2005)
  • University of Michigan (1997-2005)
  • University of Washington Harborview Medical Center (1997-2016)

APPLICATIONS AND KEY CONTRIBUTIONS

CIREN provides a unique link between real-world crash injuries, laboratory testing, and computational modeling, supporting the development and validation of injury assessment tools and criteria used in biomechanics research and crash testing. Its Bio-Tab injury causation process, first implemented in 2005, was later adopted in NHTSA’s Crash Investigation Sampling System (CISS) and Special Crash Investigations (SCI) programs. CIREN’s methods have also informed other injury research efforts, including Federal Aviation Administration (FAA) aviation crash studies and U.S. Army blast injury reviews. 

CIREN data have supported research on small overlap crashes, lower extremity, knee-thigh-hip, and lumbar spine injury mechanisms, leading to new injury criteria and expanded data collection protocols. CIREN has also supported various internal NHTSA research efforts, including case studies on brain, ankle, and thorax injuries, oblique frontal crashes, and fatalities in frontal crashes. CIREN has enabled validation of computational reconstructions using Global Human Body Models Consortium (GHBMC) models and fulfilled numerous data and medical imaging requests from academic and industry researchers worldwide. 

In addition, CIREN centers have advanced studies on the role of Advanced Automatic Crash Notification (AACN) data in improving trauma care, further extending CIREN’s impact on injury prevention, treatment, and research.

PEDESTRIAN/NON-MOTORIST DATA COLLECTION

The CIREN Pedestrian Crash Pilot Study, conducted from 2018 to 2020 at two CIREN enrollment centers, applied CIREN’s investigation and analysis methods to collect detailed data on vehicle-to-pedestrian crashes. This effort led to the development of updated protocols for pedestrian crash investigation, data collection, and injury causation analysis to support research on pedestrian crashworthiness, crash avoidance, infrastructure, and behavior. 

Building on this work, the Vulnerable Road User In-Depth Crash Investigation Study (VICIS) expanded pedestrian data collection in 2022 across four CISS primary sampling units, with CIREN engineering centers conducting the analysis. In total, 99 vehicle-to-pedestrian crash cases were collected and analyzed through these two studies, representing NHTSA’s largest dedicated pedestrian crash dataset since the Pedestrian Crash Data Study (PCDS) of the 1990s. These efforts provided the foundation for CISS to adopt nationwide non-motorist crash data collection beginning in 2024. 

FINITE ELEMENT COMPUTER SIMULATION

CIREN is advancing the use of computational human body models to support injury causation analysis and virtual testing. A CIREN contractor has developed a scalable, generic vehicle interior model along with scaled human body models based on the GHBMC to enable virtual reconstructions of real-world crash cases. This framework allows users to select either simplified or detailed models to conduct parameter studies, visualize occupant kinematics, and explore potential injury mechanisms. 

CIREN teams have assisted in applying these tools during the case review process, contributing to model validation, and feeding insights into broader virtual testing efforts. Ongoing work continues to refine the models and methods, with outputs supporting other NHTSA safety research activities focused on advancing virtual testing capabilities.

Research

Since its inception in the late 1990s, CIREN has contributed extensively to NHTSA’s safety research in an array of topics including injury mechanisms across body regions and crash modes, restraint system performance, occupant characteristics and premorbid conditions, child crash safety, and computational crash reconstruction. To date, CIREN data has supported over 200 peer-reviewed publications and more than 300 technical reports, presentations, and short communications. 

Selected Publications

Abstract – Because small overlap impacts have recently emerged as a crash mode posing great injury risk to occupants, a detailed analysis of U.S. crash data was conducted using the NASS/CDS and CIREN databases. Frontal crashes were subcategorized into small overlap impact (SOI) and large overlap impact (LOI) using crash and crush characteristics from the datasets. Injuries to head, spine, chest, hip and pelvis, and lower extremities were parsed and compared between crash types. MAIS 3+ occupants in NASS/CDS and CIREN demonstrated increased incidence of head, chest, spine, and hip/pelvis injuries in SOI compared to LOI. In NASS/CDS, subgaleal hematoma represented 48.6% of SOI head injury codes but 27.6% in LOI. Cervical spine posterior element fractures also represented greater proportions of SOI spine injuries (e.g., facet fractures: 27.8 vs. 14.0%), and proximal femur fractures represented a greater proportion of hip/pelvis injuries (e.g., intertrochanteric fracture: 32.5 vs. 11.8%). Tarsal/metatarsal fractures were a lesser proportion of lower extremity injuries in SOI compared to LOI. Occupant contact points inducing these injuries were observed in CIREN cases in some instances without compartment intrusion. These injuries suggest the substantial role of occupant kinematics in SOI which may induce suboptimal occupant restraint interaction.

Objective: To describe a new method for analyzing and documenting the causes of injuries in motor vehicle crashes that has been implemented since 2005 in cases investigated by CIREN. Methods: The new method, called BioTab, documents injury causation using evidence from in-depth crash investigations. BioTab focuses on developing injury causation scenarios (ICSs) that document all factors considered essential for an injury to have occurred as well as factors that contributed to the likelihood and/or severity of an injury. The elements of an injury causation scenario are (1) the source of the energy that caused the injury, (2) involved physical components (IPCs) contacted by the occupant that are considered necessary for the injury to have occurred, (3) the body region or regions contacted by each IPC, (4) the internal paths between body regions contacted by IPCs and the injured body region, (5) critical intrusions of vehicle components, and (6) factors that contributed to the likelihood and/or the severity of injury. 

Results: Advantages of the BioTab method are that it attempts to identify all factors that cause or contribute to clinically significant injuries, allows for coding of scenarios where one injury causes another injury, associates injuries with a source of energy and allows injuries to be associated with sources of energy other than the crash, such as air bag deployment energy, allows for documenting scenarios where an injury was caused by two different body regions contacting two different IPCs, identifies and documents the evidence that supports ICSs and IPCs, assigns confidence levels to ICSs and IPCs based on available evidence, and documents body region and organ/component-level "injury mechanisms" and distinguishes these mechanisms from ICSs. Conclusion: The BioTab method provides for methodical and thorough evidenced-based analysis and documentation of injury causation in motor vehicle crashes.

Abstract - One of the challenges in expanded use of finite-element (FE) simulations for occupant protection research is the availability of validated vehicle models that can represent varied vehicle types and safety designs. The objective of this study was to develop a publicly available, parametric FE model representing a diverse set of driver and front passenger compartments and restraint systems to enable automated and efficient population-based crash simulations. A previously published driver compartment model was expanded in this study to include the front passenger area with additional airbags. Using a mesh morphing method, the updated vehicle model was morphed into interior geometries representing four vehicles with varied sizes. All modeled restraint components are parameterised. LS-DYNA simulation results using the vehicle-specific models were compared with US-NCAP frontal and side impact tests with ATDs. Seat belt and air bag parameters were tuned to provide a good match to ATD responses. A set of population-based crash simulations were then conducted with 200 human body models with a wide range of size and shape to demonstrate the feasibility and robustness of the automated crash simulation concept. This is the first study to develop a parametric FE model of both driver and passenger seating positions.

Abstract - Motor vehicle crash (MVC) occupants routinely get a computed tomography (CT) scan to screen for internal injury, and this CT can be leveraged to opportunistically derive bone mineral density (BMD). This study aimed to develop and validate a method to measure pelvic BMD in CT scans without a phantom and examine associations of pelvic BMD with age and pelvic fracture incidence in seriously injured MVC occupants from the Crash Injury Research and Engineering Network (CIREN) study. A phantom-less muscle-fat calibration technique to measure pelvic BMD was validated using 45 quantitative CT scans with a bone calibration phantom. The technique was then used to measure pelvic BMD from CT scans of 252 CIREN occupants (ages 16+) in frontal MVCs who had sustained either abdominal or pelvic injury. Pelvic BMD was analyzed in relation to age and pelvic fracture incidence. In the validation set, phantom-based calibration vs. phantom-less muscle-fat calibration yielded similar BMD values at the anterior superior iliac spine (ASIS; R2 = 0.95, p < 0.001) and iliac crest (R2 = 0.90, p < 0.001). Pelvic BMD was measured in 150 female and 102 male CIREN occupants aged 16–89, and 25% of these occupants sustained pelvic fracture. BMD at the ASIS and iliac crest declined with age (p < 0.001). For instance, iliac crest BMD decreased an average of 25 mg/cm3 per decade of age. The rate of iliac crest BMD decline was 7.6 mg/cm3 more per decade of age in occupants with pelvic fracture compared to those not sustaining pelvic fracture. Findings suggest pelvic BMD may be a contributing risk factor for pelvic fracture in MVCs.

Abstract - Objective: Knee air bags (KABs) have become increasingly common in the vehicle fleet. Previous studies (Weaver et al., 2013; Patel et al., 2013) showed indications that KABs may be protective for some lower extremity injuries and associated with increased risk for others. Since KABs have become significantly more common in recent model year vehicles, we revisited these findings using the most recent available data. 

Methods: We compared injury rates below the knee, from the knee to the hip, and above the hip in years 2000-2015 of the National Automotive Sampling System, Crashworthiness Data System (NASS-CDS) and the Crash Injury Research and Engineering Network (CIREN). Injury rates were compared with matched analyses and with Bayesian multiple logistic regression. 

Results: Both analyses showed that KAB to have an Odds Ratio of approximately 0.6 for knee to hip injuries, with the Bayesian model strongly significant and the matched model borderline insignificant. In the Bayesian model, KAB was borderline significant for a decrease in above the waist injuries, while the matched model pointed toward a protective effect but was not significant. Both models pointed toward an increased risk of below knee injuries, but neither was statistically significant. 

Conclusions: KABs may be protective for knee to hip injuries and above waist injuries. If KABs continue to be widely implemented in the vehicle fleet, the field should continue to monitor and evaluate below knee injuries.

Data Access

CIREN Crash Viewer

The CIREN database contains detailed, structured data on motor vehicle crashes with clinically significant injury outcomes, including crash reconstruction findings and comprehensive medical injury profiles. To protect patient confidentiality, all personally identifiable information, geographic details, and sensitive medical data are removed from the public files. Publicly accessible CIREN cases, dating back to 2004, are made available once coding and quality control are complete. Additional cases are published on a rolling basis as they are finalized. 

Using the links below, users can search the available CIREN cases using a range of filter options to identify cases of interest. Vehicle-related filters include make, model, and model year, as well as crash characteristics such as impact type, crash angle, change in velocity (Delta-V), and rollover status. Occupant-specific filters include seating position, age, height, weight, and sex. Injury data can also be used to refine searches, including filters for body region, injury severity, and specific injury codes. 

CIREN data sets

The CIREN public data set contains cases with crash dates between June 1, 2005, and December 31, 2016, that have undergone the complete quality control process. A portion of the data is provided in SAS files similar to those prepared for National Automotive Sampling System – Crashworthiness Data System (NASS-CDS) annual releases, though several CIREN-specific SAS files have been created to disseminate the additional occupant and injury causation data that CIREN collects. The data files are provided with a CIREN data dictionary to facilitate their use, though users may also require NASS-CDS Analytical User’s Manual(s) to fully comprehend the data.

  • CIREN data files  (downloadable ZIP file)
    ZIP file posted September 7, 2018 with Data Dictionary v1.2.1 applicable to the 2016 data release (includes repair of missing data in OA file)

Tabular case data from cases enrolled from 2017 onward will be released in the future.

More Information

For more information on CIREN technical operations and field procedures, contact:
Human Injury Research Division, NSR-220
1200 New Jersey Avenue SE
Washington, DC 20590

You can also ask for more information or make requests by email:
nhtsa.ciren@dot.gov 

CIREN Investigator Verification: https://crashviewer.nhtsa.dot.gov/verify 

OMB Control Number: 2127-0774
Expiration Date: 03/31/2028