Accident Analysts - a Search for Traces
Author: Joachim Geiger
Every serious road accident leaves behind traces that reveal the story of how the accident happened. Finding and understanding these traces is the job of DEKRA accident analysts. But how do these experts operate at the scene? And what tools do they use? We checked with the specialist division.
Severe accidents with injuries and fatalities are still a reality on Europe's roads - in 2023, around 20,400 people were killed in road accidents across the European Union, with pedestrians, cyclists and motorcyclists particularly at risk. Each of these accidents has its own story in which courts, public prosecutors and insurance companies are interested when assessing questions of fault. The findings necessary for this are provided by accident analysis reports. “In principle, as an accident analyst, you arrive at the scene of an accident like a cinema visitor who enters the cinema at the time the credits roll and has to make up his mind what the movie was like based on that," explains Peter Rücker, Head of Accident Analysis and Accident Research at DEKRA Automobil. Tracks and vehicle end positions are the equivalent of the film credits at the scene of the accident, as are circumstances such as weather and lighting conditions.
The evidence at the scene of the accident is the main source for the accident report
“Every accident scene is unique, exactly at the time of the accident,” reports Peter Rücker. Comprehensive forensic evidence is therefore the most important basis for clarifying the course of an accident. For the accident analyst, it is important to precisely record the evidence at the site. This includes taking pictures and videos of impact marks, splinter fields and spilled liquids on the road as well as any damage to vehicles, trees and crash barriers. Sometimes, however, there is also evidence where some accident analysts would like to see significantly more traces. The impact of a pedestrian or cyclist on a car, for example, is often difficult to reconstruct from the tracks. “First of all, you can't really see anything on the road because neither cars nor pedestrians leave any traces there. In addition, the car is often only slightly damaged in these types of accidents,” says Peter Rücker. In this case, the human body itself can become a trace - bone fractures, for example, can tell us a lot about the direction of impact and the energy that was needed to cause the fracture.
Can the accident data recorder in the car support accident analysis?
Under certain circumstances, the vehicle can also contribute important information about the accident. Modern cars often have an accident data recorder (event data recorder/EDR) installed which, since July 2024, has been mandatory for all newly registered passenger cars and commercial vehicles up to 3.5 tons. The device continuously records data such as speed, accelerator pedal position, engine speed, steering angle and brake interventions, but only saves them when a certain trigger threshold is exceeded. However, Peter Rücker says he would never blindly trust the EDR data. Particularly in accidents involving pedestrians and cyclists, the corresponding recordings are often missing from the recorder because the vehicle has not been significantly decelerated by the impact. As a result, important information for accident analysis is not available. And what if the traces are not sufficient despite a thorough search? In this case, the accident analyst has to use circumstantial evidence to obtain the relevant data on driving dynamics, Peter Rücker continues. This can go as far as recreating the accident scenario in a test set-up at the DEKRA Crash Test Center using a vehicle and dummy as well as carrying out test series at different speeds - ultimately leading to a close correlation between the test and reality.
Accident analysts need to be both creative and think forensically
Nevertheless, the job of an accident analyst is not simply limited to collecting evidence. It is also about correctly assigning and interpreting the various traces of the accident. The key question is therefore how the traces found can be interpreted. “This is where an expert witness has to be creative and, above all, think forensically,” says DEKRA expert Peter Rücker. To do this, he also has excellent resources at his disposal. If, for example, an analysis involves the question of what speeds are required to cause a certain vehicle deformation, a query in the DEKRA accident database might help. This database not only stores the findings from previous accident analysis reports, but also provides the results of the crash tests that DEKRA Accident Research regularly carries out.
Tracking down real accidents with the simulation using a 3D model
New digital technologies are also used in DEKRA accident analysis. The latest evolutionary stage of 3D photogrammetry, for example, evaluates images and videos of an accident scene that the accident analyst records, sometimes with the help of drones. Special software calculates a razor-sharp 3D image of the accident site from the data. If you then feed a program for reconstructing accidents with this model along with the analyst's own calculations, this opens up new approaches to analysis. “As these programs work according to physical principles, an accident can be simulated again and again in the 3D model under original conditions with different parameters, so to speak,” explains Peter Rücker. It is also possible to carry out a final check of the determined course of the accident with this type of system. The accident analyst feeds their data into the program and runs the simulation. The virtual accident will then lead exactly to the constellation that the accident analyst found at the real accident scene. Such visualizations can also provide a better understanding of the course of the accident when it comes to court.