The ability to resolve the issue of the location of a vehicle collision by expert means and the accuracy with which it is possible to determine the location of each vehicle on the road at the time of the collision depend on what initial data about the circumstances of the incident the expert has and how accurately this location is determined.
To determine or clarify the location of the vehicle at the moment of their collision, the expert needs the following objective data:
About the traces left by the vehicle at the scene of the accident, their nature, location, length;
About traces (paths) left by objects thrown away during a collision: parts of the vehicle that separated during the impact, cargo that fell out, etc.;
About the location of areas of accumulation of small particles that have separated from the vehicle: soil, dirt, glass fragments, areas of splashing liquids;
About the location after a collision of the vehicle and objects thrown away during the collision;
About damage to the vehicle.
In most cases, the expert has only some of the listed data.
It should be noted that, no matter how conscientiously the situation at the scene of the accident was recorded by persons who do not have experience in conducting automotive technical examinations (or do not know the methods of expert research), omissions cannot be avoided, and they are often the reason for the impossibility of determining the location of the collision. Therefore, it is very important that the inspection of the scene of the incident is carried out with the participation of a specialist.
When inspecting and examining the scene of an accident, first of all, it is necessary to record those signs of the incident that may change during the inspection, for example, signs of braking or skidding on a wet surface, traces of the movement of small objects, tire tracks left when driving through puddles or leaving the roadside, areas of sprinkled earth during rain. The location of the vehicles should also be recorded if it is necessary to move them to provide assistance to victims or to clear the roadway.
Determining the location of a collision using vehicle tracks
The main signs by which the location of a collision can be determined are:
A sharp deviation of the wheel track from the initial direction, which occurs when there is an eccentric impact on the vehicle or when its front wheel is hit;
Transverse displacement of the track that occurs during a central impact and the unchanged position of the front wheels. With a slight transverse displacement of the track or its slight deviation, these signs can be detected by examining the track in the longitudinal direction from a low height;
Traces of lateral shift of unlocked wheels are formed at the moment of a collision as a result of the lateral displacement of the vehicle or a sharp turn of its front wheels. As a rule, such traces are hardly noticeable.
Termination or breaking of the skid trail. Occurs at the moment of a collision due to a sharp increase in load and a violation of the wheel lock or separation from the road surface;
The skid mark of one wheel that was hit jammed it (sometimes only for a short period of time). In this case, it is necessary to take into account in which direction this trace was formed, based on the location of the vehicle after the incident;
Traces of friction of vehicle parts on the coating when its chassis is destroyed (when a wheel comes off, the suspension is destroyed). They begin mainly near the collision site;
Traces of movement of both vehicles. The location of the collision is determined by the intersection of the directions of these tracks, taking into account the relative position of the vehicle at the time of the collision and the location of the parts on them that left marks on the road.
In most cases, the listed signs are barely noticeable, and during inspection of the scene of the incident they are often not recorded (or recorded insufficiently accurately). Therefore, in cases where the exact location of the collision is essential to the case, it is necessary to conduct an expert examination of the scene.
Determining the location of a collision using the paths left by thrown objects
In some cases, the location of the collision can be determined by the direction of the tracks left on the road by objects thrown during the collision. Such tracks can be scratches and successively located holes on the road left by parts of the vehicle, motorcycles, bicycles or cargo that has fallen, as well as traces of dragging of the bodies of drivers or passengers who fell out of the vehicle at the moment of impact. In addition, traces of the movement of small objects remain at the scene of the incident, visible in the snow, soil, dirt, and dust.
First, the objects that are discarded move in a straight line from the point of their separation from the vehicle. Subsequently, depending on the configuration of the object and the nature of its movement along the road surface, a deviation from the original direction of movement may occur. With pure sliding, on a flat area, the movement of objects remains almost linear until they stop. When rolling while moving, the direction of movement may change as the speed decreases. Therefore, the location of a vehicle collision can be determined by the traces of thrown objects, if there are signs that these objects were moving in a straight line or the trajectory of their movement is visible.
To determine the location of the vehicle at the time of the collision, lines should be drawn along the tracks of thrown objects towards the probable location of the collision - a continuation of the direction of these tracks. The intersection of these lines corresponds to the point of impact (the place where objects that left marks were separated from the vehicle).
The more traces left by discarded objects are recorded, the more accurately it is possible to indicate the location of the collision, since it becomes possible to select the most informative traces, discarding those that could deviate from the direction of the collision site (for example, when rolling objects that left them while moving objects through irregularities, when the beginning of the trace is located at a large distance.
Determining the location of a collision by the location of objects separated from vehicles
It is impossible to determine the location of a vehicle collision by the location of any parts, since their movement after separation from the vehicle depends on many factors that cannot be ignored. The location of the maximum number of parts discarded during a collision can only approximately indicate the location of the collision. Moreover, if the location of the collision is determined by the width of the road, it is necessary to take into account all the circumstances that contributed to the unilateral displacement of the thrown parts in the transverse direction.
A fairly accurate location of the collision is determined by the location of the earth that crumbled from the lower parts of the vehicle at the moment of impact. During a collision, particles of earth crumble at high speed and fall onto the road almost in the place where the impact occurred.
The largest amount of earth is separated from deformed parts (the surfaces of the wings, mudguards, the bottom of the body), but if the car is heavily soiled, earth can also fall off from other areas. Therefore, it is important to determine not only from which vehicle the earth fell, but also from which parts of it. This allows you to more accurately indicate the location of the collision. In this case, it is necessary to take into account the boundaries of the areas where the smallest particles of earth and dust fall, since large particles can move further due to inertia.
The location of the collision can be determined by the location of the debris scattering areas. At the moment of impact, shards of glass and plastic parts fly in different directions. It is difficult to determine with sufficient accuracy the influence of all factors on the movement of debris, so it is possible to indicate the location of the impact only by the location of the dispersion area (especially if it is significant in size).
When determining the location of the collision by the location of the debris in the longitudinal direction, it should be taken into account that the debris in the direction of movement of the vehicle is scattered in the form of an ellipse, the nearest edge of which passes from the point of impact at a distance close to the place of their movement in the longitudinal direction during the free fall. This distance can be determined by the formula:
Where,
Va - vehicle speed at the moment of glass destruction, km/h;
h is the height of the location of the lower part of the destroyed glass, m.
As a rule, the smallest fragments lie closest to the point of impact; large fragments can travel much further, moving along the road surface after falling due to inertia.
Based on the location of small debris, the location of a collision is more accurately determined on a wet, muddy, dirt road or on a road with crushed stone surface, when the sliding of small debris along the road surface is difficult.
In case of oncoming collisions, the impact location in the longitudinal direction can be but an example but to determine based on the location of the far boundaries of the areas of scattering of glass fragments rejected from each of the vehicles that collided in the direction of its movement. With a similar nature of destruction of the same type of glass, the maximum range of debris being thrown when they move along the road surface is directly proportional to the square of the vehicle speed at the time of the collision (Fig. 1). Therefore, the collision site will be located at the following distance from the far boundary of the area where glass fragments are scattered from the first vehicle:
where S is the total distance between the far limits of the areas where glass fragments are scattered from oncoming vehicles;
V1, V2 - vehicle speed at the moment of collision.
Figure 1. Determining the location of a collision based on the dispersion range of glass fragments
When marking the far boundaries of areas where glass fragments are scattered, the possibility of error should be excluded, i.e. consider as discarded those debris that are carried out by the vehicle during its movement after a collision.
Based on the width of the road, the collision location can be indicated approximately in cases where the scattering area has a small width and the direction of the longitudinal axis of the scattering ellipse can be determined. It should be borne in mind the possible error in cases whereThe appearance of debris on the right and left of the direction of movement of the vehicle was not the same (for example, due to the ricochet of debris from the surface of the second vehicle).
Determining the location of the collision based on the final location of the vehicles
The direction of movement and the distance to which vehicles move from the point of collision depend on many circumstances - the speed and direction of movement of the vehicle, their masses, the nature of the interaction of contacting parts, resistance to movement, etc. Therefore, the analytical dependence of the coordinates of the vehicle collision location on the values that determine these circumstances is very complex. Substituting formulas for quantities even with small errors can lead an expert to incorrect conclusions. It is almost impossible to determine the values of these quantities with the required accuracy. It follows that based on data on the location of the vehicle after the incident, the location of the collision can only be indicated in some cases.
Figure 2. Determination of the collision location based on the final location of the vehicle.
1 - vehicle at the moment of collision; 2 - Vehicle after impact
When conducting examinations in cases, the question is often raised about which side of the roadway the collision occurred between vehicles moving in parallel directions. To solve this issue, it is necessary to accurately determine the lateral displacement of the vehicle from the collision site, which, in the absence of data on tracks on the road, can be determined by the location of the vehicle after the incident.
The location of a collision is most accurately determined in cases where, after the impact, the vehicles continue to be in contact (or diverge a small distance). The transverse displacement of the vehicle from the collision site then occurs due to their rotation around the center of gravity. The magnitude of the movement of the vehicle is approximately inversely proportional to the magnitude of the mass (or gravity), then to determine the lateral displacement from the point of collision, you can use the following formula:
Where,
Yk is the distance between the centers of gravity of the vehicle after the incident (final), measured in the transverse direction, m;
Yo- the distance between the centers of gravity of the vehicle at the time of the incident, measured in the transverse direction, m;
G1 andG2 - vehicle mass, kg.
Clarification of the collision location based on vehicle deformations
The study of damage sustained by a vehicle in a collision often allows one to determine the relative position at the time of the collision and the direction of impact. So, if the direction of movement and the location of one of the vehicles that collided at the moment of impact are determined, then the location of the second vehicle and the point at which their initial contact occurred is determined from the damage. In many cases, this makes it possible to determine which side of the road the collision occurred on.
If only the location of the vehicle after the accident is known, then the direction of the impact and the probable displacement of the vehicle after the collision can be determined from the damage. The location of a collision can be determined most accurately when the distances by which the vehicle has moved after the impact are insignificant.
In collisions that occur as a result of a sudden turn to the left of one of the vehicles, it is possible to determine the extreme right position of this vehicle at the moment of impact, based on the possibility of performing the maneuver under certain traction conditions. In some cases, this makes it possible to find out on which side the collision occurred, if the deformation determines at what angle the impact was struck.
Characteristics of vehicle damage
In case of a vehicle collision, the main task of the expert study is to determine the mechanism of the collision, as well as to determine the location of the collision site of the vehicle relative to the boundaries of the roadway and the axle. When establishing the collision mechanism, damage to cars is studied (during transport and trace examination), and the main traces in establishing the location of the collision are those recorded in the accident diagram. All traces subject to expert analysis can be divided into two groups - these are traces in the form of damage to vehicles, and traces left by vehicles on other objects (roadways, road elements, etc.).
All traces in traceology are classified as:
Volumetric, having three dimensions (length, depth, width);
Surface, two-dimensional;
Visible to the naked eye;
Invisible;
Local:
Peripheral, located behind the zone of influence and formed by residual deformation;
Point and line.
Positive and negative;
Layering and peeling.
In transport traceology, traces of vehicle collisions, the classification of which was given earlier, have 9 names adopted to describe damage during transport trace examinations:
1. A dent is damage of various shapes and sizes, characterized by depression of the trace-receiving surface and appears due to its residual deformation;
2. Burrs are sliding marks with raised pieces, parts of the track-receiving surface are formed when the hard surface of particles of one vehicle comes into contact with the less rigid surface of another vehicle.
3. Breakdown - through damage larger than 10 mm (used both when examining tires and to describe damage to parts of the vehicle).
4. Puncture - through damage up to 10 mm (used only when examining tires.
5. Scratch - shallow, superficial damage, the length of which is greater than the width and without removing the surface layer of the material (despite the paint coating).
6. Layering - associated with the process of trace formation and the transfer of material from one object to another.
7. Flaking - separation of particles, pieces of metal, and other substances from the surface of an object.
8. Scraping - the absence of pieces of the upper layer of trace-receiving material, caused by the action of a sharp cutting edge of another object.
9. Pressing - pressing the victim by a vehicle to another object or between parts of the vehicle itself (used in the production of complex automotive and forensic examinations).
The most informative signs indicating the location of the collision site include traces of vehicle movement before the collision. Such marks can be traces of braking, rolling, lateral shift, slipping, etc. At the same time, establishing the location of a collision using traces of vehicle movement requires research into both the nature of their location and their belonging to a specific car and even a wheel. So, if the diagram shows a braking trace on the roadway, which was first directed straight and then sharply deviated to the side, then the location of the deviation of the traces indicates that while the car was moving, it was influenced by a shock load, which led to the deviation car movement. The occurrence of a shock load is a fact of interaction between vehicles during a collision. Therefore, when determining the location of a collision, both the location of the change in direction of the braking marks and the location of the location of the primary contact in the vehicle itself, which is established when determining the mechanism of the collision, are taken into account.
Lateral shear marks also indicate that their formation is caused by a collision between vehicles, and by establishing that certain marks belong to specific wheels of the collision mechanism, the location of the collision is determined.
Trace information indicating the location of the collision includes traces in the form of scree of earth or dirt from the lower parts of the vehicle during a collision, as well as traces in the form of scratches, burrs, potholes on the road left by deformed parts of the vehicle after the collision. In this case, when establishing the location of the collision, it is necessary to first determine which part and which vehicle left these marks on the road. This is established during an expert review of damaged cars. This also takes into account the mechanism of the collision, that is, the possibility of moving the car that left a mark on the road from the immediate location of the collision. Most often, in an accident there is only a scattering of glass fragments from small parts from cars, which, moreover, occupies both lanes of traffic. In accordance with methodological recommendations, a shower of glass fragments and other small parts of cars separated during a collision indicate only the area in which the collision was located, and not the place itself. Therefore, determining the coordinates of the collision site by the location of the scree of glass fragments, as well as bulk cargo, in this case can be done by the method of excluding territories. The essence of this method is that the scree zone is first divided into two sections and, taking into account the study of the collision mechanism, the final position of the vehicle, as well as other traces of the vehicle’s movement, do not independently carry informative signs of the location of the collision site, one of the sections is excluded. Then the remaining area is again divided into two zones, etc.
When applying this method, it is advisable to use full-scale modeling at the accident site or planar modeling in a large-scale diagram.
When installing a vehicle collision mechanism, as noted, trace information is available in the form of damage on the vehicles themselves. At the same time, in transport traceology there is no distinction between objects that form traces and those that perceive traces, because any area of damage is simultaneously both trace-forming and trace-receiving. In expert practice, establishing the collision mechanism based on damage to cars consists of the following stages of research: separate research, comparative research and natural comparison of vehicles. Moreover, if the first two stages are mandatory, without which installation of the collision mechanism is impossible, then the third stage cannot always be carried out, and the impossibility of its implementation does not depend on the expert. In this case, the expert must conduct a simulation based on the first two stages of the study. It is necessary to point out another type of trace information examined by experts during complex automotive and forensic examinations. These marks include marks on the victim’s clothing, as well as marks in the form of bodily injuries on the victim’s body. The study of such traces in conjunction with traces on the vehicle makes it possible to establish the mechanism of the collision of a car with a pedestrian.
The most difficult studies should be considered to be studies to determine the identity of who was driving the car at the time of the accident. In this case, traces on the road, traces on the vehicle, as well as traces on the bodies of people who were in the car at the time of the incident are examined.
Analyzing the above, it should be pointed out that the assessment of trace information in each specific case is individual and cannot be a once and for all established methodology, but requires abstract thinking from the expert, covering the entire gamut of traces, as well as taking into account the described evaluative features in the traces.
Application
Examples of typical relative positions of vehicles at the moment of collision (depending on the angle between their speed vectors):
1. Longitudinal, counter, straight, blocking, central, front.
2. Longitudinal, passing, straight, blocking, central, rear.
3. Longitudinal, counter, direct, tangent, eccentric, lateral.
4. Longitudinal, associated, parallel, tangent, eccentric, lateral.
5. Cross, transverse, perpendicular, blocking, central, left.
6. Cross, associated, oblique, sliding, eccentric, left.
7. Cross, counter, oblique, sliding, eccentric, left.
To understand the scale of car damage after an accident, you need to clearly understand what happens directly at the moment of impact with the car body, which areas are subject to deformation. And you will be unpleasantly surprised to learn that during a frontal impact, the rear part of the body is skewed.
Accordingly, after unscrupulous body repair of the front end, even if the car was on the slipway, you will observe the trunk lid sticking, the sealing rubber rubbing, and much more. If you are interested in this topic, I suggest that you familiarize yourself with the educational material on collision theory, which was prepared by the specialists of our educational center.
General information
Theory collisions – This knowledge And understanding strength, emerging And existing at collision.
The body is designed to withstand the impacts of normal driving and to ensure the safety of passengers in the event of a vehicle collision. When designing the body, special care is taken to ensure that it deforms and absorbs the maximum amount of energy during a serious collision, while at the same time causing minimal impact on occupants. For this purpose, the front and rear parts of the body must be easily deformed to a certain extent, creating a structure that absorbs impact energy, and at the same time these parts of the body must be rigid in order to maintain a separation area for passengers.
Determination of violation of the position of body structural elements:
- Knowledge of collision theory: Understanding how a vehicle's structure reacts to the forces generated during a collision.
- Body inspection: search for signs indicating structural damage and its nature.
- Taking measurements: basic measurements used to identify violations of the position of structural elements.
- Conclusion: application of knowledge of collision theory in conjunction with the results of external inspection to assess the actual violation of the position of a structural element or elements.
Types of collisions
When two or more objects collide with each other, the following collision options are possible:
According to the initial relative position of objects
- Both objects are moving
- One is moving and the other is stationary
- Additional collisions
In the direction of impact
- Frontal collision
- Rear collision
- Side collision
- Rollover
Let's look at each of them
Both objects are moving:
One is moving and the other is stationary:
Additional encounters:
Front collision (frontal):
Rear collision:
Side collision:
Tipping:
Influence of inertial forces during a collision
Under the influence of inertial forces, a moving car tends to continue moving in a forward direction and when it hits another object or car it acts as a force.
A car standing still tends to maintain a stationary state and acts as a force opposing another car that hits it.
When colliding with another object, an "External Force" is created
As a result of inertia, “Internal forces” arise
Types of damage
Impact force and surface
Damage will vary for given vehicles of the same weight and speed depending on the object of the collision, such as a pole or wall. This can be expressed by the equation
f = F / A,
where f is the magnitude of the impact force per unit surface
F - force
A – impact surface
If the impact falls on a large surface, the damage will be minimal.
Conversely, the smaller the impact surface, the more severe the damage will be. In the example on the right, the bumper, hood, radiator, etc. are seriously deformed. The engine is moved rearward and the consequences of the collision reach the rear suspension.
Two types of damage
Primary damage
The collision between the vehicle and the obstacle is called the primary collision, and the damage it creates is called primary damage.
Direct damage
Damage caused by an obstacle (external force) is called direct damage.
Ripple Effect Damage
The damage created by the transfer of impact energy is called ripple effect damage.
Damage caused
Damage caused in other parts experiencing a tensile or pushing force due to direct damage or damage from the wave effect is called induced damage.
Secondary damage
When a car hits an obstacle, a large deceleration force is generated, which stops the car within a few tens or hundreds of milliseconds. At this point, passengers and objects inside the vehicle will attempt to continue moving at the vehicle's speed prior to the collision. A collision that is caused by inertia and that takes place inside the vehicle is called a secondary collision, and the resulting damage is called secondary (or inertial) damage.
Categories of violation of the position of parts of the structure
- Forward offset
- Indirect (indirect) displacement
Let's consider each of them separately
Forward offset
Indirect (indirect) displacement
Shock Absorption
The car consists of three sections: front, middle and rear. Each section, due to the nature of its design, reacts independently of the others in a collision. The car does not react to impact as one inseparable device. At each section (front, middle and rear), the influence of internal and (or) external forces manifests itself separately from other sections.
Places where the car is divided into sections
Crash-absorbing design
The main purpose of this design is to effectively absorb impact energy by the entire body frame in addition to the destructible front and rear parts of the body. In the event of a collision, this design ensures minimal deformation of the passenger compartment.
Front part of the body
Since the risk of collision is relatively high for the front end, in addition to the front side members, upper wing apron reinforcements and upper body side panels with stress concentration zones are provided to absorb impact energy.
Rear body
Due to the complex combination of rear quarter panels, rear floor box and spot welded elements, the impact absorption surfaces are relatively difficult to see in the rear, although the concept of impact absorption remains similar. Depending on the location of the fuel tank, the impact absorption surface of the rear floor side members is modified to absorb impact energy from collisions without damaging the fuel tank.
The ripple effect
Impact energy is characterized by the fact that it easily passes through strong areas of the body and finally reaches weaker areas, damaging them. This is the principle of the ripple effect.
Front part of the body
In a rear wheel drive (FR) vehicle, if impact energy F is applied to the leading edge A of the front side member, it is absorbed through damage to zones A and B and also causes damage to zone C. The energy then passes through zone D and, after changing direction, reaches zone E. Damage, created in zone D is shown by the rearward displacement of the spar. The impact energy then causes ripple effect damage to the instrument panel and floor box before spreading over a larger area.
In a front-wheel drive vehicle (FF), the energy from a frontal impact will cause intense destruction of the front section (A) of the side member. The impact energy, causing the rear section B of the side member to bulge, eventually causes damage to the instrument panel (C) from the ripple effect. However, the ripple effect on the rear (C), reinforcement (lower rear spar) and steering gear bracket (lower instrument panel) remains negligible. This is because the central part of the side member will absorb most of the impact energy (B). Another characteristic of a front wheel drive (FF) vehicle is also damage to the engine mounts and surrounding areas.
If the impact energy is directed towards area A of the wing apron, the weaker areas B and C along the impact path will also be damaged, allowing some of the energy to be absorbed as it travels rearward. After zone D, the wave will impact the top of the post and the roof longitudinal beam, but the impact on the bottom of the post will be negligible. As a result, the A-pillar will tilt backwards, with the bottom of the A-pillar acting as a pivot point (where it connects to the panel). The typical result of this movement is a shift in the door landing area (the door becomes misaligned).
Rear body
Impact energy on the rear quarter panel causes damage at the contact area and then at the rear quarter panel. Also, the rear quarter panel will slide forward, eliminating any gap between the panel and the tailgate. If higher energy is applied, the rear door may be pushed forward, deforming the B-pillar, and damage may extend to the front door and A-pillar. Damage to the door will be concentrated in the folded areas at the front and rear of the exterior panel and in the door lock area of the interior panel. If the rack is damaged, a typical symptom is a door that doesn't close properly.
Another possible direction of the wave effect is the path from the rear side pillar to the longitudinal beam of the roof.
In this case, the rear of the roof rail will be pushed up, creating a larger gap at the rear of the door. The junction between the roof panel and the rear side body is then deformed, causing the roof panel above the B-pillar to deform.
When studying the mechanism of a collision in the process of approaching a vehicle, the expert establishes either a violation of stability or loss of control before the collision and the reasons for such a violation, determines the speed of the vehicle before the incident and at the moment of the collision, establishes their location at certain times, the lane, the direction of movement, the angle of contact at collision.
By examining the process of vehicle interaction, the expert establishes their relative position at the moment of impact, determines the direction of the impact and its impact on the movement under study.
When studying the process of throwing a vehicle after a collision, the expert determines the location of the collision based on the remaining traces and the location of the vehicle after the incident, determines their speed of movement after the impact, and the direction of the throwing.
Establishing by an expert the mechanism of the collision and a technical assessment of the actions of the participants in the incident allow the investigative authorities and the court to resolve the issue of the cause of the incident and the circumstances that contributed to its occurrence.
The expert research methodology for establishing the collision mechanism depends on the type of collision. According to the main classification criteria that determine the collision mechanism, all vehicle collisions can be divided into the following groups:
According to the angle between the directions of movement of the vehicle - longitudinal (when driving parallel or close to parallel) and cross collisions. Longitudinal collisions are divided into oncoming and passing;
According to the nature of the interaction at the contact site during an impact - blocking (with complete damping of the relative speed at the moment of impact), sliding and tangential collisions.
These signs characterize the collision mechanism of both vehicles. In addition, the collision of each of the two colliding vehicles can be characterized by features unique to this vehicle:
By the nature of the movement immediately before the impact - a collision without reserve, with reserve to the right or left;
According to the place where the impact impulse is applied - a side collision is right - or left, front, rear, corner;
According to the direction of the impact impulse - the collision is central (when the direction of impact passes through the center of mass of the vehicle), right - or left eccentric.
This collision classification system makes it easy to formalize the characteristics of a collision.
§ 2. Mechanism of vehicle collision
General concept of the collision mechanism
The mechanism of a vehicle collision is a complex of circumstances related to objective laws that determine the process of vehicles approaching before a collision, and the interaction during the impact and subsequent movement until it stops; analysis of data on the circumstances of the incident allows the expert to establish the relationship between individual events, fill in the missing links and determine the technical cause incidents. A formal solution by an expert to questions based on individual scattered data, without a technical assessment of their compliance with each other and established objective data, without revealing and explaining the contradictions between them, can lead to incorrect conclusions.
When studying the mechanism of an incident, signs that directly allow one to establish one or another circumstance may be absent. In many cases, it can be established based on data about other circumstances of the incident, by conducting an expert study based on patterns that connect all the circumstances of the incident mechanism into a single set.
Features of impact in a collision
The theory of impact is based on ideal conditions, which greatly simplify the understanding of the interaction of bodies during impact. Thus, it is assumed that the contact of colliding bodies occurs at one point through which the interaction force passes, that the surfaces of the colliding bodies are absolutely smooth, there is no friction or engagement between them. Therefore, the impact force is perpendicular to the plane tangent to the surface of the colliding bodies at the point of their contact. The duration of the impact is assumed to be zero, and since the force impulse has a finite value, the impact force is considered to occur instantly, reaching an infinitely large value. The relative displacement of the colliding bodies during the impact is also considered to be zero, and therefore, the mutual repulsion of the colliding bodies occurs only under the influence of elastic deformation forces.
The interaction of a vehicle in a collision is much more complex than described above. During a vehicle collision, contact between them occurs over large areas, and various parts enter into it, causing interaction forces to appear in different places. The direction and magnitude of these forces depends on the design of the contacting parts (their shape, strength, rigidity, nature of deformation), therefore the interaction forces are different at different points of contact. Since the deformation of a vehicle during a collision can be very significant in depth, the interaction forces are variable in magnitude and direction.
The collision time is very short. There, no less than the relative displacement of the vehicle during this time can significantly affect their movement after the collision.
The direction of impact in a collision and the main direction of deformation of the contacting parts do not always coincide with the direction of the relative speed of the vehicle. They can coincide only in cases where the contacting areas do not slip during the impact. If slipping occurs over the entire surface, then transverse components of interaction forces arise, causing deformations in the direction of the least rigidity, and not in the direction of the longitudinal components, where the rigidity and strength of the deformed parts can be much higher (for example, when hitting at an angle on the side of the door the surface of the cabin is deformed not in the direction of the impact, but in the transverse direction if the impact was sliding).
It is also impossible to assume that the line of impact (the vector of the resultant impulses of the impact forces) during a collision passes through the point of initial contact. If the area of the deformed area is large, the main blow can be delivered at a considerable distance from this point when interacting with stronger and more rigid parts than at the point of initial contact.
The vehicle collision mechanism can be divided into three stages: vehicle approach before the collision, interaction upon impact, and kickback (movement after the collision).
First stage of the collision mechanism– the process of rapprochement – begins from the moment a danger to traffic arises, when in order to prevent an incident (or reduce the severity of the consequences) the drivers must immediately take the necessary measures, ends at the moment of initial contact of the vehicle. At this stage, the circumstances of the incident are determined to the greatest extent by the actions of its participants. At subsequent stages, events usually develop under the influence of irresistible forces arising in accordance with the laws of mechanics. Therefore, in order to resolve issues related to the assessment of the actions of the participants in the incident in terms of compliance with their traffic safety requirements, it is of particular importance to establish the circumstances of the incident at its first stage (the speed and direction of movement of the vehicle before the incident, their location along the width of the roadway).
Some circumstances of the incident at the first stage cannot be established directly on the spot or through questioning witnesses. Sometimes they can be established through expert examination of the collision mechanism at subsequent stages.
Second stage of the collision mechanism– interaction between vehicles – begins from the moment of initial contact and ends at the moment when the influence of one vehicle on another stops and they begin to move freely.
The interaction of a vehicle in a collision depends on the type of collision, determined by the nature of the impact, which can be blocking or sliding. During a blocking impact, the vehicles seem to stick together in separate sections, and there is no slipping between them. During a sliding impact, the contacting areas are displaced relative to each other, as the speed of the vehicles is equalized.
The process of a vehicle collision during a blocking impact can be divided into two phases.
In the first phase, deformation of the contacting parts occurs as a result of their interaction. It ends when the relative speed of the vehicle in the contact area drops to zero and lasts a fraction of a second. Enormous impact forces, reaching tens of tons, create large decelerations (accelerations). With eccentric impacts, angular accelerations also occur. This leads to different changes in the speed and direction of movement of the vehicles and their turn. But since the impact time is negligible, the vehicles do not have time to significantly change their position during this phase, therefore the general direction of the deformations usually almost coincides with the direction of the relative velocity.
In the second phase of the blocking impact, after the completion of mutual penetration of the contacting sections, the vehicles move relative to each other under the influence of elastic deformation forces, as well as mutual repulsion forces arising during an eccentric impact.
The magnitude of the impulse of elastic deformation forces compared to the impulse of impact forces is large. Therefore, with a slight eccentricity of the impact and deep penetration of the contacting parts, the adhesion forces between them may prevent the separation of the vehicle and the second phase of the impact may end before their separation.
A sliding collision occurs in cases where the velocities in the contact areas are not equalized and before the vehicles begin to move away from each other, the interaction occurs sequentially between their different parts located along the line of relative displacement of the contacting areas. In the event of a glancing impact, the vehicle manages to change its relative position during the collision, which somewhat changes the direction of the deformations.
During contact, transverse velocities of the vehicles arise, which leads to a deviation in the direction of their deformations.
A sliding impact with a small depth of mutual penetration and a high speed of relative displacement is called a tangential impact. With such an impact, the vehicle speeds after the collision change slightly, but the direction of their movement will change significantly.
As a result of a vehicle collision, as well as when it hits obstacles and runs over people, various marks appear on them. Some of them appear as a result of the initial impact, others - during their subsequent movement (hitting a pole or barrier, tipping over, driving into a ditch). When analyzing the overall picture of traces, great importance is attached to identifying traces of the initial contact, since by studying them it is possible to establish such components of the accident mechanism as the direction of movement, the angle of collision, the relative position of the vehicle at the time of the collision, etc.
Traces of the primary impact (contact) appear immediately at the moment of impact with an obstacle; they usually take the form of extensive deformations, dents, scuffs, scratches, paint peeling, etc.
Collisions can be divided into three main types:
Passing - occur when the vehicle moves in one direction:
Oncoming traffic - when the vehicle is moving in opposite directions;
Angular (transverse) - when the vehicle moves at an angle to each other.
A type of oncoming and passing collisions is a side sliding collision, i.e. a collision of a vehicle with the sides (almost a glancing impact), in which the vehicles practically do not change the direction of movement (of course, if the difference in their masses is very insignificant).
A type of transverse collision is a cross collision, when vehicles collide at a right angle, i.e. the longitudinal axes of the colliding vehicles are relatively perpendicular.
When inspecting a vehicle, first of all, pay attention to the places most severely damaged by the impact, in which the direction of deformation is clearly visible. Depending on the type of collision, marks are located on certain parts of the vehicle. In the event of a passing collision, traces of the primary contact are located on the front of one vehicle (on the front bumper, fenders, radiator lining, hood, to these traces you can add broken windshields, headlights and sidelights), on the other - on the rear (on the rear wall of the body, rear bumper, on tow hooks). Damage to rear lights and reflectors is also typical; paint and wood may peel off; in addition, the rear axle may be damaged. In an oncoming collision, damage from the impact is located on the front parts of both vehicles - on the front bumpers, trims, hoods, fenders, and front parts of the cab. This type of collision is characterized by damage to headlights, sidelights, and windshields. As a result of significant impact and deformation, the glass of the cabin doors may be damaged and the doors may become jammed. In a head-on collision, a heavier vehicle can crush a lighter one; in this case, on the upper surface of the latter (on the front hood, roof of the body, etc.) there may be traces from the protruding parts of a heavy vehicle and even from its wheels. In the event of a corner collision on one of the vehicles, damage occurs at the front or rear corners. As a result of a strong impact, the front axle, the running board, headlights and sidelights can be torn off, the wheels can be separated, the front bumper is bent or crushed, and the windshield can be broken. A side sliding collision is characterized by the disruption of protruding parts and parts of the vehicle located in the side parts (corners of bumpers for some types of cars, steering for cyclists and motorcycles, side parts of the driver's cabin, fenders, door handles, external rear-view mirrors, body steps). In sliding side collisions, the contact marks are dynamic. From them you can determine the direction of impact. A cross collision is characterized by the formation of marks on the front parts of one vehicle in the same places as in an oncoming collision, and on the sides of the other (on the fender, running boards, side of the cabin or body, on the door, wheels, muffler, gas tank of the car) .
Traces of primary contact in a collision arise from the penetration of parts of one vehicle into another. Primary contact is characterized by many dents and metal displacements in a certain direction (in the direction opposite to the direction of the impact force, i.e. the movement of the vehicle).
Dynamic traces are formed when parts of one vehicle are inserted into another and end with dents, at the bottom of which trace-forming parts and parts or holes may appear. They are also located in the direction of metal deformation and are clearly expressed in the form of scratches, metal cuts, scuffs with tears, as well as the overlay and peeling of paint or rubber (from wheels).
The location of damage depends on the type of collision. The marks formed during a collision are much more pronounced than the marks formed during subsequent impacts or overturning of the vehicle.
The primary contact areas are determined by the location of the greatest metal deformation, located in one direction.
Vehicle damage resulting from overturning can be easily distinguished from other types of damage. When a vehicle rolls over, it experiences loads that are different from the loads it experiences in a collision. Some of their parts (for example, the radiator lining) are not damaged, while others (for example, the bumper) are damaged less than in a collision. During the process of turning over, the vehicle usually comes into contact with the road surface with the roof of the cabin, which is crushed. Extensive damage (dents, bent pillars) occurs on parts of the vehicle made from thin sheet steel, as they are easily subject to deformation. The resulting damage does not have a strictly defined direction, i.e. metal deformation occurs in different directions. In places where dents form, dynamic and static marks from contact with the road and various objects located on it (dirt, gravel, sand, branches) are observed. These tracks also do not have a clearly defined direction.
Traces of secondary contact can be either a continuation of traces of primary contact from a collision with a vehicle, or traces from an impact with other objects (corner of a house, pole, tree). Traces of secondary contact are usually less pronounced than traces of primary contact, since part of the kinetic energy at the moment of primary contact during a vehicle collision is lost. The deformation of the metal in these traces is either a continuation of the deformation of the primary contact (then their direction coincides), or has a different direction.
In corner and cross collisions, the vehicle often “collapses” and secondary contact marks are formed on the sides.
A side collision (sliding) is characterized by the presence of traces of primary and secondary contact of the same intensity. Traces of secondary contact (dents, scratches, burrs, paint layers) here are a continuation of traces of primary contact and are located on the side surfaces of the vehicle.
If during a side collision the driver of the car loses control, a collision with a stationary object may occur, then the deformation of parts of the vehicle has a different direction. The vehicle deformation configuration reflects the configuration of the object with which the collision occurred.
When conducting an examination to establish traces of primary contact and the sequence of damage, it is necessary to take into account all damage that occurred during the accident. They can be located not only on the vehicles themselves, but also on the road (marks from rollovers) and on objects with which a collision occurred.
Only by assessing all the traces together and comparing them with each other can one correctly determine the location of the primary contact and resolve the issue of the sequence of damage formation.
Thus, on the Moscow ring road there was a collision between a MAZ-503 and a UAZ-452. Both cars were traveling in the same direction. Due to the discrepancy in the testimony of the drivers of both vehicles, it was necessary to determine the place of primary contact between the vehicles and the cause of damage to the rear side of the UAZ-452 vehicle. During an expert examination of the vehicles, it was determined that the left side of the platform of the UAZ-452 vehicle was destroyed. There was damage on it in the form of dents and scratches directed from front to back, on the rear side of the car body there were numerous scratches in different directions, and there were no traces of impact. The right fender of the MAZ-503 car was damaged; there were traces of impact (dents, holes) and skidding marks (scratches).
When comparing the damage on the body of the UAZ-452 car with the damage on the MAZ-503 car, it turned out that the damage on the left side of the body of the UAZ-452 car coincided in nature, size, distance from the road surface with damage to the right wing of the MAZ-503 car. Analysis and comparison of the damage allowed the expert to conclude that the initial contact occurred on the left side of the UAZ-452 with the right wing of the MAZ-503.
Analysis of the damage to the rear side of the body of the UAZ-452 car, taking into account the skid marks recorded in the inspection report of the scene of the incident and the diagram for it, made it possible to establish that they were formed when the UAZ-452 car overturned after a collision and when it slid on the road surface.
In the event of a vehicle collision with a pedestrian, the following options are possible.
1. When colliding with the front part of a vehicle, a blow to the body is possible, in which the victim will be thrown in the direction of the vehicle.
In this case, the car will be damaged only from the initial contact - on the front parts in the form of dents, abrasions, blood stains, layers of particles of clothing and shoes.
In a front-end collision, it is also possible for the victim’s body to be thrown onto the car and move in the direction opposite to the vehicle’s movement. In this case, secondary traces remain, often dynamic, in the form of slip marks (rubbing marks, scratches, layers of clothing particles, blood, brain matter) on the fender, hood, driver's cabin, and car body.
If the victim's body is thrown in the direction of travel, the vehicle may run over him. Traces of the move usually remain on the lower parts of the vehicle (on the wheels, front and rear axles, truck driveshaft, gearbox, etc.).
2. When colliding with the rear of a vehicle (if it is moving in reverse), an impact usually occurs or the body is pressed by the vehicle against a foreign object (the wall of a building, a tree): there are no traces of repeated contact between the vehicle and the victim’s body. The exception is when the body is sandwiched between the side surface of the vehicle and some obstacle and is dragged between them.
3. In the event of a glancing impact from the side of the vehicle, the victim’s body is thrown to the side in the direction of the vehicle’s movement. In this case, repeated contact is usually impossible; in rare cases, a car may run over the victim’s body.
To establish traces of primary contact in a collision with a pedestrian, it is necessary to carefully familiarize yourself with the report of the forensic medical examination of the victim, examine the damage to his clothes and shoes and compare them with the damage to the vehicle.
The main types of road accidents that require ASR are collisions, which are divided into:
windshield- vehicle collision in oncoming traffic;
lateral- collision of a vehicle with the side of another vehicle;
tangent- collision of a vehicle with its sides during oncoming traffic or movement in one direction;
capsize- an incident in which a moving vehicle overturned;
hitting a standing vehicle- an incident in which a moving vehicle collided with a stationary vehicle, as well as a trailer or semi-trailer;
hitting an obstacle- an incident in which the vehicle ran over or hit a stationary object (bridge support, pole, tree, fence, etc.).
Special types of accidents that require ASR
Special types of accidents- Road accidents complicated by dangerous factors requiring special training of rescuers or the involvement of additional forces and resources.
Accident with vehicle falling into water- Road accidents in which vehicles for some reason fall into rivers, lakes, the sea, fall through ice, etc.
Accident with vehicle falling from steep slopes- Accidents in which vehicles, for some reason, fall off steep slopes and, when falling, usually roll over several times, hitting rock ledges, and fly 100–150 m or more. Sometimes vehicles explode. The vehicles themselves turn into a pile of twisted metal.
Accident on a railway section- road accidents in which: a vehicle collides with a moving or stationary train at a railway crossing or on a section of the railway not intended for crossing; A vehicle collides with another vehicle at a railway crossing; a rolling stock collides with a vehicle at a railway crossing or on a section of the railway not intended for crossing.
Accident involving a tram (trolleybus)- Accidents in which a tram (trolleybus) collided (ran over) into another vehicle, or as a result of power wires breaking and falling on the vehicle, or a tram derailing and overturning, the vehicle or people were injured.
Road accident with fire– Road accident, accompanied by fire of emergency vehicles and the cargo they transport.
Vehicle falling under a rubble- An accident in which a vehicle with people as a result of natural or man-made phenomena was caught in an avalanche, mudflow, landslide, rockfall, etc.
Accident in a tunnel (overpass)- Road accidents complicated by the specifics of a limited space, which makes it difficult to access the accident site, carry out emergency response and evacuate victims.
Accident with a vehicle carrying dangerous goods- An accident with a vehicle carrying cargo that falls under the category of dangerous, as a result of which there was a leak (ejection, fire, etc.) or there is a danger of such a situation, including:
- an accident with a vehicle transporting flammable liquids (FL) or flammable liquids, which resulted in a spill or leak;
- an accident with a vehicle transporting hazardous chemical substances (HAS), which resulted in a spill or leak;
- an accident with a vehicle transporting radiation hazardous substances (RH), as a result of which there was a spill or leakage, resulting in environmental pollution;
- an accident with a vehicle transporting biologically hazardous substances (BH), as a result of which there was a spill or leakage, resulting in contamination of the environment;
- An accident with a vehicle transporting explosives and explosive objects, in which there was a threat of detonation of explosives and high explosives due to their movement, mechanical impact on them or heating (combustion).
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