Author Mark Turner
A proper collision scene documentation, lovingly referred to as a scene doc, will make or break the investigation… guaranteed! While not necessarily all inclusive, here are a few evidence collection / documentation techniques that have served me well over the years.
Some, if not most, collision scene evidence is short lived, and tire marks are at the top of the list. When I was just a MAIT Associate… ah yes, the MAIT Associate, all of the fun, none of the worry… I remember being called out to a single vehicle fatal by the county Sergeant, The driver of the vehicle had run off the right side of the roadway and overcorrected in an attempt to regain control. The vehicle then entered into a critical speed yaw and overturned. My job was to make sure the collision scene evidence was documented properly and await the arrival of the real MAIT Team. When I first arrived on scene, the critical speed tire scuffs left by the vehicle were nice and dark with well-defined edges and striations. No problem, I thought to myself. When MAIT arrives, we’ll take chord and middle ordinate measurements for the radius, plug it into the critical speed formula, and bingo, we’ll have a good speed on our vehicle. Problem was, as I talked with my fellow Troopers, the tire scuffs were steadily fading… and I mean fading fast! I quickly gathered the tools needed, laid out two 30-foot chords, and measured the middle ordinates. The second middle ordinate measurement was larger than the first. This indicates that the vehicle is slowing and is indeed in a true yaw. With this cautionary tale in mind, how should a collision scene be documented? Well, it’s pretty straight forward, and really just common sense, but extremely important none the less… it’s a language… kind of a geek language spoken by collision reconstructionists, if you will.
With tire marks underfoot, grab a trusty can of orange spray paint and draw a line straight across at the beginning and end of the tire mark, with a single dot of paint continuing the entire length of the tire mark every few feet… and please put the paint dot in the middle of the tire mark, not beside the tire mark… don’t ask! Gouges and scratches on the roadway surface, as well as any marks made off the roadway get this same treatment. Fluid trails, whether made by a vehicle or a body, also get the same treatment. Pedestrian fabric trails…yep same. Pedestrian shoe scuffs… yeah, right?? Well, if they do exist, feel free to use this same technique.
Now that we’ve painted our finger and at least one shoe orange, let’s continue with the scene doc. Tire positions at the vehicle’s final rest also need to be documented. Mark a single line at the base of the tire for its entire length, with another single line marking the tire / wheel center, forming a “T” and indicate LF, RF, RR, etc. While not necessary if the vehicle is upright, a single line at the rear and at the front of the vehicle with an arrow indicating the vehicle’s front is nice, but it does become necessary if the vehicle is in any other position other than upright. Final rest tire marks for motorcycles and scooters can be documented similarly, and indicating a vehicle front and side is important with two wheeled vehicles. Proper documentation of a body at final rest, whether ejected from a vehicle or a pedestrian is extremely important and must be handled with a bit of care. A single paint dot at the head and another at center of mass of the body will suffice. Please don’t draw a “stick man” or write something insensitive on the roadway… the families will visit the wreck scene… sometimes while you’re there! Pedestrian clothing, particularly a hat, is important to document and can assist in determining an area of impact… designate a corresponding evidence letter or number on the roadway and list that on the field sketch… more on that in a few.
Now that the collision scene evidence is nicely painted for the most part, let’s get to taking some pictures and video. You are the vehicle! You are the pedestrian! 360 degrees, in, around, and back out! That’s it! Let’s explore… starting at a point that’s deemed… maybe it’s arbitrary, maybe it has meaning like a sight distance view, take a camera shot 360 degrees in each direction. Then, walking the direct vehicle path, take a picture every few feet with the camera lens setting as close to the capabilities of the human eye as possible, documenting the collision scene evidence as you go. Photograph around the final rest position, and back out using the same procedures. If you use a handheld video camera walking the scene or conducting a drive-thru video, document the collision scene the exact same way. The pictures and video should reflect a flow of the collision dynamics with approach movements, impact, post-impact movements, and final rest documented sequentially. Each picture that documents a specific piece of evidence or is taken for some variety of emphasis should reflect a wide view, a medium view, and a close-up of the intended subject. A great example of this is a left of center collision scene documentation, with a maximum engagement gouge in one of the travel lanes. If we know which direction both vehicles are going, then that gouge is the golden goose of the scene doc. What if we then take one zoomed in picture of the goose with no other qualifying pictures… does us no good, right? Remember, you are the vehicle! If the wreck is an active scene at night, always use the photographing technique known as “painting with light”. I won’t go into all the details of the process, but it’s basically leaving the camera’s shutter open for an extended period of time and moving a light source around until the entire scene is properly illuminated. It literally turns a night photograph into day.
Now for our old friend the field sketch… and what a warm and fuzzy friend to fall back on when we need it! If done correctly, it knows all. Some argue that the field sketch is an antiquated tool, what with all the fancy laser scanners and flying space drones out there, but not this guy! It gives me the roadway, roadway orientation, scene evidence, roadway width, lane width, lane line length and space, surrounding buildings, or trees, or sight distance measurements… really anything the heart desires… anything that’s important, and helps the investigation. So, grab a pen, paper, template, and roller wheel and let’s do this… when you’re back at the office, trying to figure things out, your old friend will be waiting.
Time for the big guns… a forensic mapping. In order to render a computer assisted drawing (CAD) of the collision scene and the collision dynamics, a forensic mapping of the collision scene and maybe the involved vehicles as well is needed. Now, is this 100 % necessary to accomplish the same goal? The short answer is no. There is always the baseline coordinate method of scaled diagraming. While a good collision reconstructionist should be familiar with this, it’s going to be a little time consuming to say the least. Luckily, there are more efficient tools available. Back when I was a SCHP MAIT investigator we used a Sokkia Total Station and prism pole for mapping… of course that usually involved a closed roadway and blue lights. These days I have far less authority to close a major travel corridor, so that makes standing in the roadway a little dicey. Thankfully, the Trimble X7 laser scanner does a fantastic job of mapping the wreck scene as I wait at a safe distance away. Gaining evermore popularity for forensic mapping, and for good reason, are aerial drones. Photographs taken by the drone, at an even safer distance for the pilot, and then processed in photogrammetry software render a scaled orthomosaic that can be imported into most CAD software programs. In some situations, just a single overhead drone picture with a visible known ground scale works just fine to produce a CAD.
A few concluding thoughts and I will close things out on this article. Never discount the availability of witnesses, even if it has been a while since the wreck happened… perhaps the corner store cashier, who was never approached by the police, saw the whole thing. Speaking of the corner store, always check for video locations around the wreck scene, even private residences. These are often very short-lived but can provide game-changing evidence for the case. Always make sure to document the location of the video camera and its angle as it relates to the roadway… this will influence any time and distance speed calculations..
Proper scene documentation is really at the heart of a good collision reconstruction… it is the ingredients for the recipe. No matter how skilled the chef… bad ingredients make for a bad dish!
Mark Turner, ACTAR #2368, is a vehicle collision reconstructionist with Warren. Prior to joining Warren, he worked for 25 years as a South Carolina Highway Patrol Trooper including 10 years as a Multi-Disciplinary Accident Investigation Team (M.A.I.T.) leader (corporal). Mark is accredited as a Traffic Accident Reconstructionist by The Accreditation Commission for Traffic Accident Reconstruction (ACTAR). He investigated in excess of 900 vehicle accidents and incidents as a trooper. Then, as a member of M.A.I.T. for 10 years, he was involved in over 1000 detailed investigations and collision reconstructions. Mark has testified multiple times in state courts and has been court qualified as an expert in accident investigation and collision reconstruction. Mark is a member of the South Carolina Association of Reconstruction Specialists (SCARS), the International Association of Accident Reconstruction Specialists (IAARS), and the National Association of Professional Accident Reconstructionist (NAPARS). He completed the Law Enforcement Basic Program at the South Carolina Criminal Justice Academy in Columbia, South Carolina.
