Impact Damage

Damage to vehicles can be a very useful means of determining accident causation, unlike the calculation of speed from skid marks things are not so simple if you want to determine a speed from damage as it does not relate pro-rata. Most independent tests related to accident damage assessment are based on 100% frontal overlap, within recent years a tendency to impact test vehicles offset to each other and a limited number of side on impacts have been explored. The results of these tests although very useful to manufacturers in vehicle design and development have little if any connection to real life accidents and therefore reflect distorted facts upon which to base any firm conclusions on the street. Very few accidents happen in such ways and of course the vehicles on our roads are always in varying states of condition and repair. To further complicate the real road accident Highway Authorities and others place what they call street furniture all over the shop for the unwary motorist to find at the most inconvenient time, nature of course also plays her part with trees and thick shrub etc.

There are computer programs and mathematical calculations that can be used which can indicate the speeds involved particularly if the directions of the vehicles involved can be shown both pre and post impact. Other calculations can be used to determine various aspects of an accident such as ‘delta V’ which means ‘the change in’, in this case speed or momentum. All physical systems follow the laws of energy conservation and linear momentum, linear momentum being the product of the mass and velocity of a vehicle. In a collision the energy of the vehicles momentum can not be destroyed or indeed created, known as kinetic energy it is used as it distorts the bodywork etc. of the vehicles involved, this distortion is commonly known as ‘elastic impact or deformation’.

Those test collisions I mention above usually involve crashing a single vehicle into a solid concrete block or similar, more recently these solid barriers have become more technically advanced, although still very much a non real life comparison. In these tests, controlled barrier tests, the results usually show a deceleration value of 15/20g, the body of the single vehicle is distorting to absorb all the energy of the impact. The tests are therefore very good at evaluating the deformation qualities of a single vehicle and if applied, with the appropriate alterations to allow for 2 vehicles, can be used to calculate the ‘delta V’. The stiffness of the vehicles involved is crucial and certainly in older cars can be something that can not be calculated due to such features as rust or poor repairs.

One thing is for sure, the total energy available to deform vehicles is fixed by their closing speeds, it is only the appearance that can be deceptive as this depends on the individual vehicle stiffness. It is not the case that the faster moving vehicle can be determined by the resultant damage only the vehicles stiffness. So, if it is so difficult to relate accident damage to speed what use is it? Speed is not the only factor in investigating a road traffic accident, it is worth about 10 -25%. The remaining 75-90% is then all important and indeed it is not unknown for minor excess speed to be discounted completely when other factors are clearly overwhelmingly causation factors. So what else can damage tell us?

Intrusion into the original shape of any vehicle is directional, force travels in the direction of the vehicles momentum until it is diverted by something immovable such as an engine or compacted body panels. If there is sufficient force even an engine will be moved but more often the direction of the vehicles changes and so does the direction of the forces involved. This results in angular distortion to body panels pulling other panels and components from their original positions in life. By careful examination of these distortions and identifying the first point of impact it often becomes clear in which direction the force was initially travelling. In this way the vehicles involved can be placed diagrammatically at the appropriate angles to each other at impact.

This process however only places them at angles to each other it does not place them on the road at any particularly angle. For this we must rely upon more traditional evidence such as the good old witness or of course tyre marks, gouges in the road surface etc. Do not forget that damage is not confined to one plane, it can be at almost any angle and of course these angles, up, down or at any angle in between, can often reveal a considerable amount of evidence. Rolling vehicles have very distinctive marks, vehicles have leading edges at varying heights and these points often over-ride or under-ride each other leaving strange markings and dents.

Why is this important?

When you brake heavily the weight of the vehicle is transferred forward and the front of the car drops on the suspension. If a car with a high front bumper gets under the back end of a low rear bumpered car in a rear end shunt it would indicate that certainly the rear of the 2 cars was braking hard at the point of impact. Bear in mind that if the front of a car dips under braking the rear will lift so some examination of the 2 vehicles involved is necessary. The rear car could be braking hard and at its lowest point at the front, equally the front car could be braking hard with its rear as high as it will go, result high fronted bumper slips inexplicably under rear of lower bumpered car. This example demonstrates the extremes of damage that might be found, more common perhaps is the over ride when damage to a rear tailgate on its lower edge will perhaps show a lack of braking on the matched height rear vehicle. A little imagination and some reference to publicly available data can provide probable proof or at least good advocacy arguments.

Hopefully the reader will appreciate the value of vehicle damage the difficulty that remains however is how to collect and preserve such evidence, it is not always possible or cost effective to send an agent to make such a record prior to the disposal or repair of the vehicles involved. Many recovery garages and some assessors take photographs although it would not be good policy to rely on these sources of information. By far a more reliable method is to ask the policy holder/client to take a few snaps, if you intend to do this ensure they are aware of certain requirements.

Photographs should be taken from a measured distance away from the car, that distance is best maintained in each photograph taken. A frontal view, from the centre of the vehicle, both side views again from the centre of the length of the vehicle and a rear view from the centre of the vehicle. Then a view along the length and width showing all sides and finally at 45’ angles to each corner. These photographs are best taken at the same height from the ground which should be about the same height as the bonnet. Flash should not be used due to the reflection of light from the paintwork. Photographs of the vehicle interior showing distortion of dash boards, steering wheels etc. are also necessary. In all some 12 - 20 pictures will be necessary.

From these photographs valuable information can be discerned and commented on by those professing to be experts in the matter although there is no substitute for the real thing. Whenever possible and most certainly in the more costly claims direct access to both vehicles involved would be the only means of securing a comprehensive opinion. One final comment on vehicle damage is that of mechanical failure. I include the matter because in general terms vehicles rarely fail these days due to a mechanical fault, (the exception ‘ wheel loss’). If they do it is either a new car with an inherent design fault or poor maintenance. Inherent design faults are more common than you might think as the industry is renowned for its policy of testing vehicles on the public, although in fairness there are very few serious failures in this category. In those rare cases when inherent failure occurs you will certainly need to seek the help of experts in the motor industry to track down vehicle recalls and warnings from manufacturers.

Component failure is again rare and most fitter failures are the result of the DIY experts or using a chap down the road who does a good job cheap. Again in these cases you will need to consult an expert to get started.

How will you know when there is a possibility of any such failure? Listen to your client, when the driver says the car did not do what was expected there may be cause for concern. It is my experience that only on the odd occasion does anyone even hint at the accident being the cars fault and subject to my comments under ‘skidding vehicles’, when they do it is worthwhile taking a look at the car as soon as possible.