Archive for the ‘Subjects’ Category

Valuable Evidence Collected from Vehicles

Wednesday, March 10th, 2010

As part of a thorough vehicle examination we will first look at the evidence that can be collected from the various lamps on the vehicle. Many times the question arises in an accident about whether or not someone had their headlamps on low or on high beam. Were they using their turn signal? Or were other basic indicator lights illuminated? Sometimes as a result of the collision there may be scientific evidence that may be collected from a bulb or even its remnants that could help answer these question

Second let’s consider the vehicle’s tires. Depending on the circumstances surrounding the accident there may be questions about tire failure. Valuable evidence regarding this can be collected from a careful inspection. Also the tires could be overly worn or improperly inflated and lead to a hydroplaning incident. Or maybe the tires are unevenly worn indicating a possible alignment issue. Also it is important for accident reconstruction purposes to know if the wheels became pinned or locked due to the collision because this affects the post-impact energy-speed calculations.

Next we can look at the damaged areas. When considering vehicle damage it is important to distinguish between contact damage and induced damage. As the terms imply, contact damage is damage to a vehicle caused directly by contact with another vehicle or object. Induced damage is damage that is produced by the collision forces but did not directly make contact with any outside object. Some items of evidence that can be collected from damaged areas include surface abrasions, windshield damage, imprints, tire prints, and paint transfer. Also we want to measure the crush profile and determine the principle direction of force.


Surface abrasions usually result when a vehicle overturns but can result when a vehicle scuffs up against an object or rigid body such as a median wall. When the vehicle slides over a surface it will produce scratches in the vehicle’s paint. The orientation of these scratches can be helpful in determining the movement of the vehicle as the marks are being made.  

With windshield damage it is important to distinguish between induced and contact damage. It is also important to note that some windshield contact damage can result from the deployment of vehicle airbags. If it is determined to be contact damage not from an airbag, it could be from an object outside the vehicle such as a motorcycle or bicycle rider. In this case it would indicate the movement of the rider after the impact with the striking vehicle. The windshield damage could also result from an occupant or some other object inside the vehicle. This information can help determine occupant position and the direction of the collision forces.
Tire prints are similar to imprints however they do not typically leave an impression but a different kind of distinct marking. Sometimes during a collision the tires of one vehicle will rub up against the body of the other leaving a rub mark or tire print. In the case where the front wheel of a semi-tractor rubs up against a vehicle, the lugs can produce circular tears in the metal along with the tire rub mark.




Another bit of evidence that can be helpful in determining the orientation of the vehicles or even which vehicle hit another vehicle at different points in a multi-vehicle accident is paint transfer. Many times paint from one vehicle will be transferred onto the other vehicle where they make contact. Although many times this evidence may be obvious there are other times where it is very miniscule and requires careful examination.

Finally by looking at and taking measurements of the damaged vehicle we can produce a scale diagram of the vehicle and its deformation. This is helpful like the tire prints and paint transfer in determining the way the vehicles came together in the collision. Also it can sometimes be used with crash test data to determine an impact speed for the striking vehicle. Also we can look at different components of the vehicle that were displaced during the collision and take note of the direction of their displacement from their original placement to get an idea of the principle direction of force that was applied to the vehicle. This can be helpful in confirming other calculations and in understanding occupant kinematics.


This article is not exhaustive but serves to highlight the fact that a lot of valuable evidence and data can be obtained from a careful vehicle inspection. This information can assist in answering questions that arise when investigating the causes of vehicle accidents.


Jonathan McGehee



Speed Calculation in a Motorcycle Accident

Friday, December 18th, 2009

“I never saw him, he came out of nowhere, he must have really been flying” are common familiar sayings in motorcycle accidents. This article deals with the vault formula and slide to stop method for calculating the speed of a motorcycle involved in a crash where another vehicle pulls out in front of an oncoming motorcycle. In crashes where the front of the motorcycle impacts into the front or rear sections of an automobile, pickup or some object that allows the rider to vault over the handle bars and continue flying through the air until it impacts the ground, the vault formula method may be used.

In cases where the motorcycle impacts into a large vehicle where the occupant does not clear the collision area such as when it impacts into a semi tractor or trailer, the formula can not be used.  An example of the type of impact where the vault formula can be used is seen in diagram 1.

In order to calculate the departure speed of the motorcycle operator several bits of information are needed:
  • The horizontal distance that the operator travels from the point of impact to the first touch point on the roadway and the final rest location
  • The departure/takeoff angle of the motorcycle operator
  • The height of the center of mass of the motorcycle operator above the first touch point
  • The coefficient of friction between the operator’s clothing and roadway surface
The distance needed for the vault portion of the calculation is the horizontal distance from the location where the motorcycle operator is located at the point of impact with the car, pickup truck or object to the point on the roadway or grass where the driver or rider lands.  The distance needed for the slide to stop portion of the calculation is the horizontal distance from the location where motorcycle operator first touches the ground to its final rest position. Sometimes there is good evidence on the roadway apparent at the scene investigation of where the motorcycle operator impacted the ground and many times there is not. A thorough scene inspection at the earliest time after the accident by a trained eye will have the best opportunity to find this evidence. A scale diagram will normally be made to document the impact point, final rest locations and other pertinent information from which measurements can be made to determine the proper distances for the calculations.

The takeoff angle for a motorcycle operator is generally between 10 to 20 degrees. The takeoff angle for the passenger varies depending on the type of motorcycle and operator position of the particular accident and can be as low as 18 to 20 degrees and  as much as 45 degrees.

When making the field measurements with total station technology or other methods, (steel tape and level) elevation changes between the roadway at the point of impact and the landing point need to be made. This will allow an accurate measurement of the vertical  distance that the operator traveled from the point of impact to the first touch point.

Adding the height of the center of mass of the driver (located usually at the belly button point) from the top of the seat height of the motorcycle will give the  starting height at the point of impact. Subtracting the elevation change to the ground level and then adding ½ the thickness of the body will give the height above the ground distance needed in the calculation. An estimate can be made by bracketing the distance if the exact height is not known.
The formula is as follows:


V = feet per second
g = acceleration due to gravity (32.2 feet per second squared)
d = total horizontal distance
A = components of 15º departure angle
Y = vertical height of driver or rider (negative value if below takeoff point)

Be sure to convert the feet per second calculated value to miles per hour by dividing feet per second by 1.467. After calculating the vault speed, the next calculation checks the calculation by calculating the slide to stop speed from the first touch point to the final rest point. Measure the distance from the first touch point to the final rest of the operator. Use the measured distance in the slide to stop formula and compare the answer with the vault speed. If the two speeds are roughly the same it’s a good indication that the answer is valid.

Slide to stop formula:

S = √ (30df)

S = √ (30*37.5*1)

S= √ 1125

S = 33.54 mph


S = miles per hour
d = total horizontal distance of motorcycle driver or rider slide
f = coefficient of friction of motorcycle driver or rider (either sliding or tumbling based on                                    injuries and scene data)
g = gravity (32.2 feet per second squared)

Studies show that the coefficient of friction between the operator’s clothing and the roadway surface for cotton/ wool and polyester is between .7 to .85 g’s and for leather is between .6 to .7 g’s. When a body does not slide but tumbles the coefficient of friction is approximately 1.0 or higher. There may be a combination of sliding and tumbling so the slide to stop coefficient of friction may vary.

By using this method a calculation can be done with the vault formula and then the slide to stop calculation can  be done to check the vault speed. If the distance used in the vault formula produces a speed that is consistent  with the speed from the slide to stop formula then that speed is how fast the motorcycle was traveling at the point of impact. If the speed from the vault formula is to high to produce a speed low enough to match the slide to stop speed then use a shorter distance for the vault and a longer distance for the slide to stop formula. Narrowing in on the right distance by trial and error, the investigator will be able to find the solution that fits both equations and   that is the approximate speed that the motorcycle was traveling when the impact occurred.

After calculating the motorcycle’s impact speed then use the skid to stop formula using the pre-impact skid distance of the motorcycle to obtain the skid-to-stop speed for the pre-impact skidding of the motorcycle. Then take that answer and combine that speed with the impact speed of the motorcycle by using the combined speed formula to calculate the start of skid speed of the motorcycle. The combined speed formula is as follows:

The combined speed formula

S = √ (S1²+S2²)

Example:   Motorcycle pre-impact skid distance is 34.6 feet. The coefficient of friction used in the calculation is .7 g’s. Assume that the motorcycle is able to obtain 100% of the coefficient of friction.

Slide to stop:                            Combined Speed:

S1 = √ (30*34.6*.7)                  S = √ (33.5²+26.9²)

S1 = √726.6                             S = √ (1122.25+723.6)

S1 = 26.95                                S = 42.96 mph

The start of skid speed of the motorcycle in this case is approximately 43 mph.

Todd Hutchison

The Value of Demonstrative Evidence

Thursday, September 3rd, 2009

Quality Photographs

As the saying goes, a picture is worth a thousand words. Well a picture serving as demonstrative evidence is equally powerful. It enables the investigator to document all aspects of the scene, vehicles, and any other valuable evidence for future reference and analysis. Additionally it enables others such as claims adjusters, lawyers, other investigators, juries, and judges to examine the scene, vehicles, or other evidence for themselves.

In regard to this last point, it must be emphasized that the photographer needs to be knowledgable about how to take accurate photographs that are true representations of the evidence. Care must be taken in the use of special lenses or filters that may distort the perspective or appearance of the shot. However, as long as proper equipment and techniques are used, a photograph generally tends to be considered irrefutable evidence.

Scale Diagrams

A scale diagram is another useful piece of demonstrative evidence. Assuming it is based on accurate measurements of the scene and vehicles, it can be used to very accurately depict locations and speeds of vehicles at different times as the vehicles approach and depart from the area of impact. Also line of sight or other important characteristics of the particular accident can be represented graphically to enhance understanding. These diagrams are helpful to the reconstructionist for doing analysis and calculations. They are useful to other interested parties to be able to visualize how the accident occurred and to understand the reconstructionists conclusions.

Animations and Simulations

Finally we will look at animations and simulations. Due to the advances in computer technology we are now able to generate these pieces of demonstrative evidence that are arguably the most advanced and self explanatory available. Although it may be self-evident we will define the difference between an animation and simulation. Both are videos generated from a series of either two-dimenisional or three-dimensional shots that show the vehicles moving through space and the accident sequence. However, the movement of an animation is completely directed by the animator whereas the movement of a simulation is generated by a computer program designed to replicate how a vehicle would move, react, and deform in an accident scenario in the real world. This algorithm is of course then based on general principles of engineering and physics. The animation allows the reconstructionist to put together his entire analysis, calculations, and measurements into one package and via this video show how the accident occurred. Simulations, assuming the algorithm is sound and propertly applied, are useful for testing theories and analysis. Click below for an example of each:



Jonathan McGehee

Conservation of Linear Momentum

Friday, July 24th, 2009

The Conservation of Linear Momentum method is a well established scientific too utilized by the reconstructionist to determine the impact speeds of vehicles involved in collisions. It is one of the many useful techniques that an accident reconstructionist has at their disposal. Others include Conservation of Energy, Critical Speed Analysis, and the Crush Factor Method. Conservation of Linear Momentum utilizes several inputs that require careful evidence collection and analysis. Additionally, some of these inputs are more sensitive than others depending on the particular situation. Next we will list the inputs and discuss some of the methods used for determining the proper value to use.

Needed Inputs:
  • Angle at Start of Post Impact Rotation
  • Angle at End of Post Impact Rotation
  • Lock-up value per Wheel
  • Weight distribution per Wheel
  • Post Impact Drag Factor
  • Post Impact Travel Distance
  • Grade in Area of Post Impact Travel
  • Approach Angle
  • Departure Angle
  • Total Weight
Accurate documentation of the vehicles, roadway, and crash scene markings is necessary. This can be done with total station technology or some other accurate method of measurement. A drag sled can be used to determine drag factors on various surfaces. Other methods such as skid tests or drag factor tables in certain instances are necessary. This documentation which is used to make an accurate scale diagram is then utilized to obtain values for the above variables. Data from the vehicle and crash scene markings will be used to determine the inputs for the lock up factor which in turn will be used for the departure speeds. Other values like the weights of the vehicles are normally obtained from professional databases like expert auto stats and then combined with the estimated weights of the occupants and cargo.

Conservation of Linear Momentum analysis, which is a scientifically sound method used by reconstructionists for calculating impact speeds and other information about crash vehicles, yields good information when proper data is inputted. The method requires several inputs some of which may be sensitive. Consequently, it is imperative that a detailed analysis and an experienced professional evaluation of the data be performed to obtain accurate results.

Todd Hutchison

The Challenges of Forensic Structural Investigations

Friday, June 12th, 2009

Causes of structural damage

VCE structural engineers are often tasked with determining the cause of a structural collapse. Such structural failures may result from design errors, construction errors, natural events, or other man-caused events. Often, more than one cause contributes to a structural failure. A windstorm can cause collapse of an inadequately braced masonry wall during building construction. Roof trusses which are not laterally braced during erection can roll over and collapse under their own weight. The structural investigator must evaluate the circumstances and make educated judgments as to the failure mechanisms, the trigger mechanism initiating the failure, and the causes of individual and progressive failure events. As may be seen in Photo1, determination of these issues can sometimes be a formidable task.

Photo 1. Light gauge steel structure collapsed during construction. Cause was determined to be Inadequate lateral bracing of steel roof trusses during erection.

Windstorm and Water Damage

After severe windstorms, a claimant will often scrutinize his building looking for damage. It is not uncommon for claimants to assume that a storm has caused newly discovered drywall cracks, foundation cracks, or other defects which may have actually resulted from prior foundation settlement or other long-term building construction or normal wear and tear issues. This phenomenon is also common in blasting and vehicle-building impact claims. Sometimes, cracking in masonry buildings and foundations, attributed to storm damage by a claimant, is found to have been previously caulked or contains mold in the cracks. A trained eye can distinguish between new and prior building damage.

Water damage to building interiors also requires skilled investigators to distinguish between damage from prior rainwater leakage through roofs and that which would have occurred during a storm for which the insured has filed a claim. Mold develops on building components and finishes after a period of time, not within several days. Dry-rot of wood takes much longer. The investigator must be keenly aware of these nuances when determining causes of damage from rainwater intrusion.

Figure 1. Tornado Track

The structural investigator is not so much concerned as to whether a windstorm is a tornado or straight line wind because the insured’s coverage is typically not dependent on which type of windstorm caused damage to his property. Tornado tracks such as shown in Figure 1 may be obtained from the local weather bureau. Additional information such as linear tornado velocity and estimated fastest 3-second ground wind speeds are sometimes available from weather agencies, but quite often this information is not available until several weeks after a storm event. Qualified structural investigators must have the skills to accurately distinguish one storm type from another by the type of wind damage and, to a high degree of accuracy, estimate the ground wind speed which caused structural damage and damage to nearby trees or man-made features.

Whether covered damage or not?

Photo 2. An insured claimed this retaining wall partially collapsed as the result of a windstorm. Investigation showed that failure resulted from improper design and construction of the un-reinforced block & brick veneer wall and foundation supporting the wall. Roots of a nearby maple tree contributed significantly to tilting of the retaining wall.

VCE’s structural engineers are guided by principles of ethics which require their reports to truthfully represent the facts, to the best of their knowledge and belief. Insured claimants should not be presumed to be making false claims. The purpose of insurance is to protect the insured from losses resulting from covered perils. A claimant is entitled to compensation for damage caused by an insured risk event. Although it is natural for investigators to sympathize with a claimant regarding the losses he has incurred, the structural investigator must use his skills to accurately determine the cause of the damage and render a fair and impartial judgment in his report. In one case a claimant stated that a 4 inch deep snow had caused his roof and ceiling to bow permanently downward. Given the worst case scenario, wherein the snow may have blown into drifts and been rained upon and refrozen, the maximum roof load which the investigating engineer calculated was less than the 20 pounds per square foot, 7-day roof live load for which roofs in the United States are required by codes to be designed. In addition, the residual deflection of the roof was found to be less than the limits for roof dead load deflection permitted by current and previous building codes.

Primary duty of the investigating structural engineer is public safety

Photo 3. Laterally buckled wood roof/ceiling trusses were found in the attic of an old church sanctuary building. Had the laterally unsupported wood board top chord been further stressed by roof loads, the ceiling and framing would have likely collapsed onto the church congregation. The investigating engineer warned the church trustees of the impending collapse of the roof and occupancy was terminated until remedial construction of the roof/ceiling framing was completed.

It is not uncommon during structural investigations to discover structural conditions which constitute a hazard to building occupants. In such cases, it is the duty of the structural investigator to inform the owner of the risk to life if the building is not evacuated or is occupied before remedial construction is undertaken to correct the structural defects in the building. In some cases this has resulted in VCE engineers making on-the-spot decisions to inform the owner that a building should not be occupied, or that limited entry is advisable only for removal of valuable assets which may be damaged by building collapse, remedial construction, or rainwater intrusion. In cases where a threat to life or the possibility of injury to occupants exists, it is the duty of the investigating engineer to give prompt notice to the owner of the potential consequences of entering a building. It is also the duty of the investigating engineer to be certain of the facts in making such a judgment.

VCE has investigated many damaged buildings, the owners of which have felt certain could not be repaired. Structural investigators are often pressed by owners to render an on-the-spot opinion as to whether a building can or cannot be repaired. When requested to do so by an insurer, VCE may, if the evidence is obvious and incontrovertible, render an on-site opinion of feasibility of repair after the investigation. More often than not, however, careful study of the investigative photography to determine potential causes of the building failure, and the application of sound principles of structural mechanics in the investigation are warranted before a proper opinion can be rendered.

Jim Waller, P. E.


Contributing Factors: The T-Bone

Friday, November 7th, 2008

There are a wide variety of contributing factors associated with vehicle accidents, and careful analysis is required to fully and accurately determine fault because of these many factors. For instance, let’s consider the case of a “T-Bone” type collision.

In this hypothetical collision, there is a Chevrolet traveling south on Hwy 11 when a Nissan pulls out from a side road into the path of the Chevrolet, and the Chevrolet impacts into the passenger side of the Nissan. Who is at fault in this collision? That can depend on several factors. Below is a partial list of possible contributing factors for each vehicle.


Nissan Chevrolet
Disregarded a Stop Sign Speeding
Failed to Yield the Right of Way Inattentiveness
Headlights Not Illuminated Headlights Not Illuminated

Only through a careful and thorough investigation can fault be accurately assigned. Our accident reconstructionists can typically confirm or disprove which of these were in fact the cause(s) of the accident. The following are various questions about contributing factors that you might have and the corresponding methodology we have available to answer those questions.

Question: Did the driver disregard the stop sign?

Answer: Based on impact speed and acceleration calculations we can determine whether it is reasonable for a vehicle to reach its speed after stopping at the stop sign.

Question: Was the vehicle speeding?

Answer: We can do various calculations to determine speed based on damage patterns, departure angles, and final rest locations. Also, we may be able to download crash data recorder information that can answer this question.

Question: Was the driver paying attention?

Answer: Based on speed/time/distance calculations, we can determine the approximate location where and the time when the driver perceived the hazard of the other vehicle and began to react. Then, we can attest to whether or not this information is consistent with a typical and attentive perception and response.

Question: Were the vehicle’s lights on?

Answer: In most cases this can be determined by forensic evidence that can be documented and collected.

Other questions that we consider and have the ability to analyze and address include:

· Was fog present creating a sight distance and headlight issue?

· Did sun glare obstruct or limit the view of the driver?

· Were the ambient light conditions such that the vehicle would have been visible?

· Were the proper traffic controls in place and appropriately located?

· Did the environmental conditions call for a reduction in the reasonable speed to be traveling?

As you can see, it is not a simple matter to say one or the other party is at fault. It takes a conscientious consideration of many possible factors.

Jonathan McGehee

Decade Long Eleven State Study of Blasting Damage Claims

Friday, November 7th, 2008

 Recently, VCE Inc. completed a 10 year, 11 state engineering study of 2,250 blasting damage claims from 1999 to 2008. These investigations were made in Tennessee, Kentucky, Virginia, Nevada, California, Georgia, South Carolina, North Carolina, Alabama, Arizona and Utah. The investigations were made over the last decade and intended to determine if blasting vibrations, or other related forces, were responsible for claimed damages. It was determined that blasting damage claims resulting from ground vibrations damage are valid less than 1.3 percent of the time.

I decided to publish this information in an article in order to address a reoccurring question I have received from many adjusters and homeowners. “Does blasting ever cause damage to structures?” The details of this study and the examples of specific blasting damage and non-blasting related damage causation conditions are best detailed in a short seminar where numerous photos could be used to illustrate some of the study’s findings.

It was determined that valid blasting damage occurred as a result of impact damage associated with fly rock, air concussion stressing, instantaneous reverse stressing associated with ground vibration and crater zone soil shifting related stressing.

The majority of the claimed blasting damages were found to be caused by something other than blasting. These non-blasting causes have included constructions defects, wind damage, thermal and moisture related stressing, differential settlement or other soil related issues, cross grain contraction and seasoning of wooden members, termites, carpenter ants and other insect related wood damages, as well as hydrostatic pressure in the soil. This study examines in detail damages from fly rock, air concussion, ground vibration and soil shifting on numerous residential and commercial structures.

The study contains 1,872 blasting claims in Tennessee, a state whose geology requires blasting for most utility line installations, mass grading for site preparations, highway construction and mining. The valid blasting damage claims have occurred in vibration ranges consistent with previously documented levels for various structural materials.

The study established that valid blasting damages resulting from any direct or indirect blasting related force occur less than 3.5 percent of the time. Blasting damage occurred in the studied structures as a result of fly rock 0.27 percent of the time, they resulted from air concussion 1.82 percent of the time, they resulted from ground vibration 1.29 percent of the time, and they resulted from soil shifting within the crater zone 0.09 percent of the time. It is important to note that this study was simply based on investigations of structures that had a blasting damage claim and did not include the countless number of structures in the areas adjacent to the same blasting activities that not only did not have any damage, but who also did not file a blasting damage claim.

While blasting was not often found as a cause of damages associated with many blasting damage claims, it was on occasion responsible for the damages. Competent experts with direct experience in blasting related stresses and damage forces can identify these damages when they occur.

 Wade Hutchison

Understanding Tennessee Blasting Standards Act Changes in 2008

Monday, July 7th, 2008

In 1975 Tennessee enacted their first Blasting Standards Act. At that time a 2.0 peak particle velocity vibration limit was set. Compliance with this limit allowed blasting contractors to monitor with a seismograph capable of measuring peak particle velocity in 3 mutually perpendicular directions. A blasting contractor could also comply with this limit by loading their blasts in accordance with a standard table of distance, which prescribed the maximum load of any 8 millisecond delay period giving the closest exposure distance to a particular blast.

 In January of 2008 the vibration standard for this law has been changed. Since 1975 several administrative changes have been made to the law; however, this is the first time that the vibration standard has changed. The Tennessee Blasting Standards Act still allows a blaster to comply with the vibration standard portion of the law by utilizing a standard table of distances for all blasts located within 300 feet of a structure; however, now the law utilizes two different formulas for blasting in areas located between 300 – 5,000 feet and for blasts located in areas greater than 5,000 feet from a particular blast. These formulas are shown in Figure 1.

 The vibration standard is no longer a flat 2.0 inches per second (in/s). The vibration standard has been divided into 2 sections. The first standard is strictly based on distance. If blasting occurs within 300 feet of a structure, the contractor is allowed to blast up to 1.25 in/s. If blasting occurs between 300 and 5,000 feet of a structure, a blasting contractor is allowed to shoot up to 1.00 in/s, and if blasting occurs at distances greater than 5,000 feet a blasting contractor is allowed to shoot 0.75 in/s. Each of this vibrations measurements are made in in/s peak particle velocity. The law also allows an alternate standard. The blasting contractor has the option of using the OSM frequency based curve for compliance. This frequency based curve allows a blasting contractor to shoot up to 2 in/s for those blasts where the vibrations occur in a higher frequency range above 30 hertz. The following graph shows the alternate OSM frequency based vibration limit.


Previously, the Tennessee Blasting Standards Act has not mandated an air blast level for any blasting activity; however the new law enacted on January 1, 2008, specifies that all blasting will be conducted at levels not to exceed 140 decibels. As a result of current changes VCE, Inc. and PMT, Inc. have cooperated in manufacturing a new version of seismograph software. This software allows seismograph users to identify compliance of measured data with the new law. The message of noncompliance will also be displayed on LCD, which will allow fast and affective blasting adjustment throughout the project for the explosive companies.


Eric Grigoryan


Preserving the Accident Scene

Monday, July 7th, 2008

Consider yourself in the following scenario: You contact us to investigate an accident that occurred a year ago. We arrive at the scene. We attempt to gather evidence, but there appears to be no evidence to collect. There are no skid marks, no gouge marks, no fluid spills and the road is repaved. Trees may have been cut down or trimmed. Road signs have been moved. The vehicles are gone, nothing was marked, and the police did not take any photographs. We attempt to locate the vehicles to inspect their damage and find that they have been repaired or salvaged. As you can imagine, our ability to replicate this incident has become increasingly difficult.


The previous example is extreme, but nevertheless emphasizes the importance of preserving evidence as soon as possible. In accident reconstruction, our analysis can only be as accurate as the evidence we gather. As time goes on the evidence degrades, and as the evidence degrades so does the ability to determine what happened with certainty. This fact puts us continually fighting against the clock because a significant amount of scene evidence is short-lived and fleeting. For instance, impending skid marks, ABS skid marks, debris patterns, and paint transfers are typically moved or nowhere to be found within a few hours or days.


After Longer Periods of Time the Following Can Also Be Altered or Removed:

  • Roadway Signs (especially in construction areas)
  • Roadway Drag Factor (further traffic degradation or re-pavement)
  • Sight Distance Obstructions (embankments, trees, parked vehicles, etc.)

This is just a partial list but it stands to emphasize the point.


When an accident occurs, consider the benefits of taking timely action.  Ideally we would be able to respond to the scene immediately after the original incident, especially if there is any indication that a comprehensive, professional investigation may be required. This gives us the opportunity to document the scene thoroughly and accurately.


We utilize various methodologies and technologies to document the scene including:

  • Quality Digital Photography
  • D.A.R.T. LX-2 Drag Sled
  • Crash Data Retrieval System
  • Sokkia Total Station
  • Nikon Reflectorless Total Station

VCE has been utilizing the Sokkia Total Station to measure accident scenes with great accuracy and precision for over 10 years. This instrument allows you to measure points at the scene in a three-dimensional framework based on distances and angles to produce X, Y, and Z coordinates that can be used with our software programs to create precise two-dimensional and three-dimensional scale diagrams, animations, and simulations. Just recently we have expanded our services to include a Nikon Reflectorless Total Station that allows measurements to be taken without the necessity of a reflector pole. This is a great asset when attempting to take measurements of a busy intersection or interstate where it would be impractical to stand in the roadway with a reflector pole. Furthermore it is ideal for measuring damage profiles of vehicles.


With our thorough scene investigation complete, the scene and evidence are recorded and saved. The facts of the particular case can be preserved for whatever future analysis might be necessary. With this information, you can make an informed decision about the requirement of further investigation based on our initial findings without the additional pressure of capturing the evidence before it is gone.


Jonathan McGehee

Slip and Fall Claims

Thursday, February 7th, 2008

A large number of people are injured every year in the United States due to falls in public places.  The majority of these falls are classified as “Slip and Fall” accidents.


The determination of the cause of such accidents is a complex undertaking and involves a large number of variables. 


One of the variables is a property known as the coefficient of friction between two surfaces.  In the case of a person walking, this is the determination of the resistance to slipping between the shoe or other foot covering and the surface on which the person is walking. 


There are several methods of measuring the coefficient friction.  The methods range from simple friction sled methods to highly technical measuring devises to determine the static coefficient of friction (SCOF).  VCE uses both in investigations of slip and fall accidents.



The SCOF of a surface is generally reported as a value from 0.00 to 1.0, the slipperiest being at the low end of the scale, and the more slip free, near the 1.0 value.


In the case of sidewalks, floors or other walking surfaces, it is generally accepted that SCOF values of 0.50 and above do not present a slip and fall hazard and values below 0.50 are slip and fall hazards.  American’s With Disability Act requires that a level walking surface have a SCOF of 0.6 or greater and a handicap ramp has a SCOF of greater than 0.80.


Contamination of the walking surface or shoe soles is often the cause of Slip and Fall accidents.  Either type contamination can greatly reduce the effective coefficient of friction.  In the case of the walking surface, spills such as grease, water, etc. are usually quite apparent, however, contamination of a person’s shoes can be less obvious. 


It is important that the Adjuster determines, if possible, the actions of the fall victim immediately prior to the accident.  This Investigator has worked on cases where there was confusion as to whether the victim was actually entering or leaving a building or coming or going to a table in a restaurant when the fall occurred.  Obviously, the source of potential shoe contamination is important in the determination of fault.


Herb Stewart