Crash Investigation Procedures

Explore the investigation procedures

To guarantee homogeneity in the investigation process and a high quality of the collected data, each team should be following common investigation procedures to ensure consistency in the data collection and the reduction of human errors.

They usually should cover the following aspects:

Road traffic crash scene investigation
Vehicle exterior investigation
Vehicle interior investigation
Personal Protective Equipment investigation
Witnesses: interviewing to people involved into the road crash
Investigation and collection of injury information

Further information can be found in our report, In-depth database: structure, tools and methods.

Road Traffic Crash Scene Investigation

Road environment investigation is a fundamental component of crash analysis and reconstruction. Investigators collect evidence from the crash scene, including: vehicle positions; impact points; skid marks; debris; road characteristics; traffic controls; weather conditions.

Data should be gathered not only at the point of impact but also from the road section leading up to the collision, typically 50–100 metres, to support reconstruction of pre-crash events. Because crash scenes often cause traffic disruption, investigation methods must be both efficient and accurate. While traditional manual tools remain available, digital technologies such as photogrammetry, drones, and total stations offer faster, more precise data collection and can generate detailed 3D models and orthorectified images, making them increasingly valuable for crash documentation and analysis.

Comprehensive scene investigations acquire the following:

Vehicle point-of-rest (POR)
Vehicle point of impact (POI)
Vehicle skid marks
Vehicle scratch marks (mostly for powered two-wheeler vehicles)
Debris and vehicle’s liquids position and scattering
Ground human-body rest position and biological finds (if any)

Capture Vehicle's POR, covering it from multiple angles to provide a comprehensive view of its position relative to the crash scene.
Photograph the area around the most probable impact zone, ensuring all relevant evidence is captured. Pay particular attention to ground skid and scratch marks, as these can offer insight into the dynamics of the crash.
Document pre-impact skids: Walk backward from the impact area to document the paths followed by each road user (vehicles, pedestrians, cyclists) during their pre-impact stage.
Take photographs approximately every 10 meters to ensure thorough coverage, capturing both the road and the vehicle at rest positions.
Cover at least 50 meters of road before the vehicle's point of rest is a crucial step in documenting the events leading up to the crash: movements, positions of the vehicles and other road users offer valuable context.
Maintain consistency in photographic techniques and angles throughout the report to facilitate analysis and reconstruction of the crash scene. Use landmarks or reference points in the surroundings to provide spatial context.

Good practice for photographic reporting of crash scenes

Vehicle Exterior Investigation

Vehicle exterior investigation focuses on documenting damage, impact marks and deformation patterns to understand crash dynamics and reconstruct the sequence of events. Evidence from the vehicle body and undercarriage can help estimate deformation energy, determine vehicle positions at impact, and assess interactions between road users. Accurate exterior data collection is also important for crash reconstruction and vehicle crashworthiness analysis, supported where relevant by standard classification systems such as CDC and TDC.

Investigators should look for:

Vehicle damage, distinguishing pre-existing from crash-related damage.
Evidence of vehicle-to-vehicle contact, such as deformation, scratches, and rubber transfers.
Tyre marks left on other vehicles or objects.
Evidence of vehicle-VRU interaction (pedestrians, cyclists, riders), including fibres, hair, blood, and abrasion marks.

Take photographs from at least eight angles, plus a top/overall view.
For photogrammetry, capture overlapping images (minimum 50% overlap) to support 3D reconstruction.
Include a measuring scale or reference object where possible to enable accurate scaling.
Take detailed photographs of all relevant damage and traces, including fibres, hair, blood, abrasion marks, and scratches.
For crashes involving vulnerable road users (VRUs), focus on areas such as the bumper, bonnet, windshield, and fenders.
Document details within their wider context by taking photographs that progress from overall views to close-ups or by using numbered references.

Photographing the vehicle

Measure damage to determine the extent of vehicle deformation and intrusion caused by the crash.
Create a damage profile and compare it with the vehicle’s original, undeformed shape.
Record damage in three dimensions: horizontal position; vertical position; and depth of deformation
Take measurements at different heights to capture the full damage profile.
Common measurement tools include: measuring tape or metric rod; laser distance meter; total station; laser scanner; photogrammetry.
Digital techniques such as laser scanning and photogrammetry can generate 3D vehicle models (point clouds), enabling detailed deformation analysis and comparison with undeformed vehicle models.

Measuring vehicle damage

Example of a vehicle damage profile superimposed to the undeformed vehicle shape, and the relative Crash-3 measures

Vehicle Interior Investigation

The vehicle interior investigation focuses on assessing passenger compartment deformation and the performance of passive safety systems, such as seatbelts, airbags, and child restraint systems. Investigators document damage, intrusion, occupant contact points, and biological traces (e.g. fibres, hair, blood) to better understand occupant kinematics, injury mechanisms, and the effectiveness of safety features.

Detailed photographs and observations support crash reconstruction and help identify how injuries occurred during the collision.

Wearable protective equipment investigation

For vulnerable road users (VRUs) such as cyclists and motorcyclists, investigators should assess the type and condition of any personal protective equipment (PPE) worn at the time of the crash. This includes helmets, protective clothing, gloves, boots, and other safety gear. Examining PPE damage helps evaluate its effectiveness, understand injury mechanisms, and generate evidence to support future road safety improvements. Investigators should document all marks, abrasions, cuts, fractures, and other damage to both the equipment and the user.

Source: Small, M., & Addo-Ashong, T. (2021). Road Safety Strategies for African Cities: A Guide to Development. Washington, DC: SSATP.

Document all visible damage, including abrasions, cracks, cuts, and fractures.
Take photographs from overall views to detailed close-ups.
Inspect the retention system and verify whether it remained secure.
Assess shell damage, including its type, severity, and location.
Record the helmet's wearing status (properly fastened, unfastened, ejected, etc.).
Document key helmet characteristics:
- Type (e.g. full-face, open-face, bicycle)
- Size and manufacturing year
- Certification standard (e.g. ECE, DOT, SNELL)
Where possible, retain the helmet for further laboratory analysis.

When examining the helmets:

Interviewing witnesses

Conducting interviews with road users regarding a road traffic accident is a multi-faceted task. It encompasses emotional significance, legal context, and practical considerations. Establishing a productive interview relationship requires special attention to the following factors:

Conduct interviews as soon as possible

Interview road users while memories are still fresh and before accounts are influenced by discussions with others or media reports.
Ensure the interviewee is physically and emotionally capable of participating.
If injuries prevent an on-scene interview, conduct it at the hospital as soon as practicable.

Use a two-stage interview process

Initial interview: a brief interview at the crash scene or hospital to capture immediate recollections and key facts.
Follow-up interview: a more detailed discussion within 48 hours to clarify events and collect additional information based on preliminary investigation findings.

Use open-ended questions

Encourage interviewees to describe events in their own words before asking specific follow-up questions.
Focus on understanding:
- Road, weather, and traffic conditions
- Actions and decisions before the crash
- Driver perceptions, reactions, and avoidance manoeuvres
- Vehicle movements and interactions
- Distraction, fatigue, time pressure, and route familiarity

Verify information and improve accuracy

Use both forward recall (describing events chronologically) and backward recall (working backwards from the crash) to identify inconsistencies and improve reliability.
Clarify uncertainties without leading the interviewee toward a particular answer.

Build trust and rapport

Introduce yourself, your organisation, and the purpose of the investigation.
Explain how the information will be used and reassure the interviewee about confidentiality and data protection.
Use empathy, active listening, and a non-judgemental approach to encourage open communication.

Prepare before the interview

Review available crash information, including vehicle involvement, crash configuration, and scene evidence.
Conduct a team debrief where possible to identify knowledge gaps and key topics to explore.
Avoid assumptions or preconceived theories that could bias questioning.

Document contributing factors

Explore factors that may have influenced behaviour, including stress, workload, secondary tasks, conversations, navigation activities, or reduced alertness.
Record observations consistently and objectively.

Respect the interviewee throughout the process

Recognise that road traffic crashes can be traumatic experiences.
Allow sufficient time for responses and avoid pressuring the interviewee.
Maintain a professional, respectful, and supportive environment at all times.

Investigation and collection of injury information

By documenting the type, severity, and location of injuries, investigators can better understand injury mechanisms, occupant and road user kinematics, and the relationship between crash forces and injury outcomes. The classification of road traffic injury severity can vary depending on the source and purpose of classification.

Combine information from hospitals, emergency services, police reports, and on-scene observations.
Gather medical records, diagnostic imaging, treatment information, and injury assessments where available.

Collect injury data from multiple sources

Apply AIS coding to classify injuries by body region and severity.
Use injury severity scores to support crash reconstruction, injury causation analysis, and safety research.

Use standardised injury coding

Work with healthcare professionals, forensic specialists, and crash reconstruction experts to interpret injury mechanisms and outcomes.
Use expert input to improve the accuracy and reliability of findings.

Collaborate with medical and forensic experts

Medical classifications focus on injury severity, treatment needs, and long-term health outcomes, often using systems such as ICD-11.
Crash investigation programmes typically use the Abbreviated Injury Scale (AIS) and Maximum AIS (MAIS) to assess injury severity in a road safety context.
Police classifications are generally based on observable outcomes and crash circumstances and may not provide the same level of medical detail.

Understand differences in injury classification

Record the number and location of injured persons.
Document visible injuries and the positions of casualties.
Capture photographs and detailed notes to support later analysis.

Conduct on-scene injury assessments

Investigate how injuries occurred, including contact with vehicle interiors, other road users, the road surface, or roadside objects.
Document injury patterns such as bruises, lacerations, fractures, and internal trauma.

Analyse injury mechanisms

Store injury data, photographs, medical reports, imaging records, and severity scores in a structured and secure manner.
Ensure information is traceable and available for future analysis.

Maintain comprehensive records

Obtain the necessary ethical approvals before collecting or accessing medical data.
Protect the privacy and confidentiality of crash victims.
Ensure informed consent is obtained where required and comply with national data protection regulations when handling health information.

Follow ethical and legal requirements