Low-Speed Damages and Injuries


Patrick Sundby, Accident Investigator



We have discussed the fallacy of “no damage = no injury” in depth in other papers, but as a reminder, we are interested in the relationship between injury and force experience, not damage induced. The phrase “no damage, no injury” is no more than “deceptive rhetoric” and draws a false causal relationship because it is based in subjective interpretation, dogmatic beliefs and too often, who is paying for your opinion. The extent of the damage, as viewed by each person, varies based on each person’s perspective. For example, what color is the square on the left?


What color is the square on the right?

The majority of the viewers of this article should say the squares are blue, but is it possible someone else sees the colors differently? What if this article was read in print form in black and white? What if the screen settings on a reader’s computer were out of adjustment? What if a reader has a condition which alters the way they see certain colors?

Taking the last variable, if the person with the condition sees the squares as something other than blue, are they wrong? No. To him/her, they genuinely see something else. This example demonstrates the subjective interpretation of the two colors presented to you in the squares.

So how do you resolve this subjective approach to the colors? You need to use an objective standard to gauge the colors against thus allowing you to determine if the colors presented are indeed blue.

In the electromagnetic spectrum, there is a small window in which visible light is located.

Within this small window, modern science has defined the wavelengths of different colors.

Rather than debating the colors of the two squares we can measure the wavelengths and compare them to the objective standard if both squares measure between 450 and 495 nm (nanometers) then both squares are indeed blue.

In the same sense of objectively defining colors, we need to objectively define the relationship between damage and injury. This relationship is defined, objectively, through force. If we can quantify the forces exerted on the vehicle (and by extension the occupant), then we can objectively compare those forces to known standards for injury. This MUST BE the method for defining the causal relationship between a vehicle collision and occupant injury vs. relying on dogma, rhetoric and financially influenced opinions because it relies on physics and the inherent mathematical facts.

Imagine being in a high-risk category for cancer and when at an appointment the doctor stands back, looks you up and down - while clothed, and says “you don’t look sick therefore you don’t have cancer.” This is the same practice when reconstruction is done via an insurance estimate. Ask yourself, how can you possibly know the extent of the damage to a vehicle when you didn’t even remove the bumper cover? When we consider the recent Allstate’s “QuickFoto Claim” where you take a picture of the accident, and they send you a check is a brilliant business move. The unsuspecting claimant thinks that getting a check quickly is a resolution of the damages to their car without ever inspecting the damages below the “skin of the car.”

When considering transference of forces and potential bodily injury, after a complete vehicle exam is done, we can assign a known value for the vehicles change in acceleration. This process can take place via a few avenues. For the sake of this paper and topic, we are going to use the Coefficient of Restitution (CoR).


If we can determine the post-impact speeds, we can then mathematically work the pre-impact speed for the striking vehicle thus eliminating any unknowns. Finally, we can check the work and ask if the results appear reasonable. (Remember 30 divided by 100 is also .3)

Consider the following case:

In this event, we have a typical lower speed collision. This vehicle was rear-ended while stopped and the occupant suffered injury. Further, there is the ever-present claim that “little/no damage = no injury.”

There is clear damage to the bumper cover and rear liftgate as well as some panel fitment issues at the corners. I’m highly suspect if we examined the structure of the bumper, we would find more evidence of the collision, and this would further support an appropriate CoR. After an examination of the vehicle, we could reasonably assign a high CoR to this event and work backward to the striking vehicle’s impact speed. While this would be of interest and worth exploring, we have complete tasks similar to this in previous discussions. This collision is important as there is a second and more specific point highlight. Consider the interior shot of this vehicle.

Consider what the chunk of missing steering wheel tells us. First, we know your average person doesn’t have the strength to tear the steering wheel. We can conclude the force of the collision did this, but how? The occupant was holding the wheel when the vehicle was struck. The collision accelerated the vehicle forward, and the occupant did not move at the same time. Once the occupant had “stretched out,” (the slack or bent arms at rest was gone) the force of the collision was translated to the steering wheel through the occupant. The question is, how much force?

The forces experienced by the steering wheel would be whatever percentage of body weight the occupant had in the torso times the “g-forces” calculated. In simpler terms, if the upper body of the occupant weighed in at “X” pounds, the steering wheel experienced this weight times the g-force. Take a quick second and consider if you had the steering wheel in your hands, what could you do to break it in a similar nature? Jump in it? Have a friend hold one side and pull? What does it really take to do damage like this? This concept is a bit of a trick question, any answer you provide is subjective – lets objectively try to determine the forces at play. This is where you put aside pre-conceived “beliefs” and allow the mathematics of physics to render answers because there are no beliefs in math equations.

When we examine the nature of a low-speed event, we will have to determine the g-forces the occupant experiences. For this example, we will utilize the following the following equation:

Initially, it appears very high values can be substituted, and the formula would still be correct. However, this doesn’t pass a sanity test. While the striking vehicle is not provided, we are assuming it’s the same or negligibly different from the KIA. We know the collision is not 100% efficient so the post-impact speed of vehicle two being 10 mph is not reasonable. In the same sense, the post-impact speed for vehicle one being zero is also not reasonable. (WHY?) We are going to use eight and two, respectively.

If the KIA was accelerated to 8 mph (11.76 fps), we could determine the g-forces be 3.65 at the lumbar spine. We also know the forces experienced at the cervical spine can be two to three times more than the lumbar, 7.3 to 10.95, respectively. These forces greatly exceed a plethora of known standards for cervical spine injury.

The process we just went through provides an objective conclusion for the forces that acted on the vehicle, and ALL of these values are a reasonable fit for the damage profile.

There is one final consideration, the broken steering wheel. The occupant holding the steering wheel would have forces act on them differently likely resulting in different injuries or increasing the forces acting on the body. A case-by-case evaluation for each collision and each occupant is a necessity to thoroughly and accurately establish the objective relationship between the forces the vehicle experienced and the forces the occupant experienced – Indeed, “no damage = no injury” is a myth.

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 Low-Speed Crash Does Not Mean LOW ENERGY


High Speed, HIGH ENERGY can = Serious Bodily Injury

Low Speed, HIGH ENERGY can = Serious Bodily Injury

The Injury Arbiter: Energy


Patrick Sundby, Accident Engineer



The modern age, say the last 100 years, has done more to advance mankind than at any other time in our history.  Great strides have been made in technology, health, and transportation.  The advancements in transportation have made even the farthest corners of the earth accessible in only a few hours. As a point of reference:  From Los Angeles to Washington D.C., the SR 71 Blackbird made the trip in under 70 (yes, seven – zero) minutes… almost 30 years ago.

While this fast-paced pattern of “make, then break” records has become the new norm, there are some ideologies in each industry which persist in urban myths, dogma or just plain falsehoods and must be tirelessly worked to dispel them.  With regards to transportation, one of the most egregious misnomers is the slower you go, the less likely you are to be injured and this falsehood is easy to dispel because physics and inherent math verifies the truth.

Before we explore this myth, let's discuss the physics of injury.  Why can we go so fast, (2,200 miles per hour in the case of the Blackbird’s trip) and not be injured yet we fall a few feet and break a bone?  The answer is “time”.  The time it takes to speed up or slowdown coming to a complete stop is what causes injury (death if severe enough).  “It's not the fall, it's the sudden stop at the end.”

Consider the advancements in vehicle safety and design.  There was a time when vehicles did not have any safety equipment.  These vehicles would crash and stop; under Newton’s laws, the occupant would keep going at the same speed the vehicle was traveling at and collide with the interior of the vehicle. In this collision, there was the sudden stop for the car, but not the occupant; the result… Injury.

The safety advancement: Lap belts.   You no longer hit the inside of the vehicle in a crash, the seat belt did its job to keep you from the sudden stop but the lap belt put extreme, sometimes paralyzing strain on the occupant’s body.  The lumbar spine is not designed to keep the top half of you in place during a crash and there is the space that normally resides between the occupant and the seatbelt at some point. Again, in a very short amount of time, the occupant is forcibly colliding with the seat belt, even if it is an inch. However, different parts of the spine are not designed to support adjacent regions with these forces and the adjacent spinal regions have to attempt to stabilize forces it was not intended to stabilize.

The safety advancement: Shoulder belts.  These were designed to restrain your upper body and not stress your lumbar spine and again you couldn’t hit the inside of the vehicle in a crash.  The shoulder belt did its job to keep you from the sudden stop and hitting the interior of the car,  but this design has some flaws too.  First, it can distribute the forces unevenly across your body.  Secondly, now that your upper body is restrained, your cervical spine has to keep your head in place during a crash – a job it's not designed to do. In addition, the sudden stop of your body means your organs can crash into your skeleton and each other.

The safety advancements: Airbags & designed failure of the seatbelt.  Most vehicles on the road today have a big bag of air waiting to deploy in the event of a collision and for front-end collisions, the sensors are located in the front, while the side airbags have side sensors, and both will only deploy if those respective sensors are activated through significant force and resultant deformity of the vehicle.  This bag is coupled with seatbelts which will stretch at a predetermined point, and the goal of both is for you to not be stopped so suddenly, in other words, to attempt to give you more time to come to a complete stop.  

The safety advancement: Crumple Zones.  Manufacturers discovered they could make a vehicle fail in a way that was predictable.  This expected behavior meant the vehicle could take extra time to crush (usually in milliseconds) and further extend the time it takes an occupant to slow down.

Safety Advancement Conclusion: These advancements in safety do nothing if the nature of the collision renders them useless or the collision is not violent enough to “need” them (low speed).  Seatbelts and Airbags do nothing for an occupant of a vehicle which is rear-ended.  If a vehicle has a collision which is not severe enough to deploy the airbag and stretch the seatbelt then both these features are useless for safety. If the vehicle cannot crumple or does so minimally, then the occupant doesn't get the benefit of the energy absorbing design. The safety advancements in modern vehicles are designed to increase the time it takes for you to slow down, but if they are not available to you (as is the case in low-speed crashes), then you are no better off than being in a vehicle with no safety features at all. 

The next logical question, "How fast can you go and still have the collision be low-speed AND suffer an injury?" is a complex one.  There are dozens of variables which dictate the outcomes of a crash, and as such, each item is a subject onto itself, however, to list a few vehicle types, vehicle mechanical condition, speed, the angle of collision, etc. The answer will come from the math of the forces involved, along with the vehicle and occupant “known information;” the weight of the car and the occupant, the speed of the vehicle, the braking distance, etc. and then apply it to a sample to illustrate how to understand Low speed can equal high energy. 

We are going to focus on the forces transferred from one vehicle to another.  Understanding how a vehicle behaves in a low-speed event and how the forces are transferred is the key to the debunking the myth of “low speed = no injury” because it is not about the speed, it is about the energy the occupant is exposed to as a result of the crash.

Let’s make the vehicle simpler, a cart with a seat…

(Credit: GM Owners Manuals)

For the moment, let us assume the collision doesn't use the crumple zones or any built-in, predictable, deformation to the advantage of the occupant.  We will also assume there are two carts and striking cart weighs twice what the victim cart weighs (including any occupants) and the striking vehicle has a post-impact speed of 4 miles per hour.  

Some basic calculations result in us knowing the change in speed for the red cart to be 12 miles per hour.  Further, if the change happened in .1 seconds the red cart occupant would experience 5.5 gs at the lumbar spine. 

To fully understand how that is derived, and the injury potential, we need to calculate the “G-Forces” the occupant’s body is exposed to in this “low-speed” model. It’s all in the math (physics) that is often confusing, but the final numbers bear significant injury potential.

Now, in the real world, the vehicle will always absorb some of the energy, the transfer is never 100% efficient.  Let's change the scenario a little bit.  What happens if both carts absorb 10% each, totaling 20% of the speed lost to crumple zones? 

Again, if the change happened in .1 seconds the red cart occupant would experience just over 5 g’s at the lumbar spine.

The math here is greatly simplified for a demonstration of concept, (energy absorbed) is a complex process detailed in other programs.  The above is not a proven method for actual collision reconstruction.

In both examples 10 miles per hour is a very striking low speed in the grand scheme; it’s a common collision speed among parking lot and heavy traffic collisions.  The g-forces experienced at the cervical spine are two-three times that of the lumbar spine.  In both examples, the cervical spine would experience at least 10 g's to 15 g’s of force, which is well above the injury threshold at either end of the spectrum. 

Let’s add some real-world context to this concept.  Below are photographs from the NHTSA database.  The listed change in velocity for this vehicle is 12 miles per hour.

This vehicle was also rear-ended, the listed change in velocity is 8 miles per hour. 

In both cases, the database reports (See the links to the NHTSA below) at least a cervical spine injury, but as you can see, there is little damage to the vehicles.  While several factors must be considered to determine if the injury is a result of a car collision, at the same time, the lack of damage or appearance of speed doesn't negate the possibility.  




Injury can, and often does, occur in what seems to be the most miniscule collisions.  There is no validity to “low speed = no injury” as that is nothing more than an “urban myth” or dogma.


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