When is a Skidmark not a Skidmark?

Tire marks are probably the most often confused and misinterpreted of all roadway evidence. A tire mark is the general class of marks left by a tire, whether rolling or locked. A skid mark is left by a locked, sliding tire.

There are different types of tire marks associated with a traffic accident investigation. The most common a private investigator will observe are:

  • Scuffs: made by a rotating or yawing vehicle, a vehicle acceleration, or a flat tire
  • Yaw mark: made by a tire that is rotating and sliding sideways parallel to that wheel’s axle; also referred to as sideslip or critical-speed scuff marks
  • Skids: made by a locked wheel caused by the application of the brake
  • Prints: made by a rolling tire
  • Scrub mark: left by a wheel locked due to damage

Skid marks are further identified in the following ways:

  • Pavement grinding: caused by material embedded in the tire grinding along the surface of the roadway (can be hard to see)
  • Tire grinding: caused by the tire itself being ground by the abnormalities of the road surface (can also be hard to see)
  • Erasure: caused by a sliding and locked tire erasing or removing any loose materials from the road surface so that area appears clean (this is frequently seen but is the most commonly ignored skid mark)
  • Squeegee: caused in a similar way as erasure and removing moisture
  • Soft foreign-material smear: caused when snow, mud, or soil that has been smoothed or spread
  • Bituminous material smears: caused when a tire is hot enough to smear tar and asphalt (the most commonly measured segment is referred to as a skid mark)
  • Tire smear: caused when a tire is hot enough to smear the rubber from the tire; usually seen on concrete surfaces
  • Shadow: the part of a skid occurring prior to any pavement grinding; supposedly always present; more often than not extremely difficult to detect; and almost always very difficult to document or image
  • Skip skids: caused by deformities in the road surface, or a vehicle weight shift
  • Gap skids: caused when releasing and reapplying brakes during a skid
  • Furrow: caused by a sliding, non-rotating wheel creating a plowed depression in soft material so that material furrows on each side; no tire print is visible
  • Rut: caused by a rolling tire in soft material; the tread pattern is usually visible
  • Acceleration marks: typical scuff mark made when sufficient power is supplied to the driving wheels and at least one-wheel spins on the roadway surface; begins as a J-shaped mark, caused by initial fishtailing as the tires heat and seek traction; the beginning of the scuff is usually very dark, and the mark gradually disappears
  • Roadway art: produced when drivers back up and then shift gears to move forward before they have stopped going backward
  • Flat tire scuffs: made by a seriously underinflated or overloaded tire; a partially deflated tire produces marks that are heavy on the edges and light in the middle; with a completely deflated tire, the sidewall touches the roadway, causing scalloped and wavy marks, and rim cuts are commonly seen.
  • Scuff Mark: a tire mark from a wheel that is both rotating and slipping: acceleration scuffs, yaw marks, flat-tire marks.
  • Scrub Marks: a skid mark caused by the vehicle being redirected as a result of a collision; marks generally look like irregular shaped smears and are characteristic of the point of impact

The proper identification of tire marks is an important part of an accident investigation. Each tire mark is produced by a specific action of the vehicle during the traffic accident event. Tire marks can tell the private investigator about what a driver did or attempted to do prior to and after a collision. A point-of-impact (POI) or an area-of-impact (AOI) can determined which is an extremely important part of the traffic accident investigation.

The proper interpretation of tire marks can tell the private investigator which, of the many, speed calculation formula to be used. For example, a vehicle left a 150-foot tire mark on a paved roadway prior to running off the road. If the tire mark is identified as a yaw mark and the specific formula for that type of mark is used, a speed calculation of 48 mph is determined. That same mark if identified as a straight skid will yield a speed of 56 mph. An 8-mph difference may not mean much unless the posted speed limit is 40 mph.


Collision-Avoidance Systems


Once in the realm of science fiction, it seemed incredible that a vehicle would be able to “see” other vehicles or pedestrians, anticipate collisions, automatically apply the brakes or take corrective steering actions and even drive itself. But this advanced technology is becoming increasingly available and more cars can do this to some degree.


Some of these systems have been around for a few years, mostly on high-end luxury cars. Collision-avoidance systems are getting better and are rapidly becoming a standard addition to new cars and not just a high-end option.


The Insurance Institute for Highway Safety (IIHS) has added collision-avoidance system testing to its suite of safety evaluations. They have determined that some of these collision-avoidance systems could prevent or mitigate many crashes. To win a top overall safety score, a car needs to have a forward-collision warning system with automatic braking and any autobrake system has to function effectively in formal track tests. To view the test results or to check if a vehicle has collision-avoidance systems available, visit the IIHS website at: www.iihs.org/iihs/ratings/crash-avoidance-features.


National Highway Traffic Safety Administration (NHTSA) is considering making some collision-avoidance systems mandatory. NHTSA’s 5-Star Safety Ratings note which systems are available on cars they crash-test but their presence doesn’t affect the rating. The cost of collision-avoidance systems can still be an obstacle with most advanced systems being part of a large options package or on a model’s higher, more expensive trim versions. The options can add thousands of dollars to a vehicle’s price.



Lasers, Radar, and Cameras


These active safety systems rely on numerous sensors, cameras, lasers, and short- and long-range radar which monitor what is going on around the vehicle. Other vehicles, pedestrians, cyclists, as well as the vehicle itself and even road signs are all monitored. Data is processed by computers, which then prompt an action from the car or the driver. These actions may start with attention-grabbers, such as a beep, a flashing dashboard icon, a tug from the seatbelt, or a vibration in the seat or steering wheel and if the driver doesn’t respond, the more advanced systems then apply partial or full braking force. Research has found that when a warning system emits too many inappropriate alerts, then there is temptation to switch it off.


Not every system on the market today is top-notch. But there’s a net benefit regardless. Even if the systems fail to prevent a crash, that crash is going to be less severe than it would have been otherwise. These systems can prevent crashes from happening in the first place.


Adaptive Cruise Control (ACC)


ACC allows the driver to select the cruise control speed and following gap. ACC detects if there is a vehicle in your path and either accelerate or brakes to maintain the selected following distance. If ACC cannot apply sufficient braking because of approaching a vehicle too rapidly, ACC will alert the driver.


Rear cross-traffic alert


Cross-traffic alert warns you of traffic approaching from the sides as you reverse. The warning usually consists of an audible chirp and a visual cue in either the outside mirror or the rear camera’s dash display. The more advanced systems can also pick out bicycles and pedestrians.


Forward-collision warning (FCW) and autobrake


Also called a pre-crash warning system, these systems warn drivers of an impending collision by using visual, auditory, or physical cues. Most vehicle systems also pre-charge the brakes and take other steps to prepare for impact. If the driver ignores the warnings, systems with autonomous braking, or autobrake, will apply partial or full braking force. They can be active at anywhere from walking to highway speeds.


Blind-spot monitoring (BSM) and assist


A blind-spot monitoring system uses radars or cameras to scan the areas beside and behind you, looking for vehicles entering or lurking in your blind zones. When such a vehicle is detected, an illuminated icon appears in or near the appropriate side-view mirror. If you signal a turn while a car is in your blind zone, some systems send a stronger alert, such as a blinking light or louder chirps. More advanced systems help keep you in your own lane by applying the

brakes on one side of the vehicle.



Pedestrian detection and braking


Pedestrian detection can recognize a person straying into a vehicle’s path. Some will automatically apply the brakes and newer systems can also detect bicyclists.



Adaptive headlights


As you turn the steering wheel adaptive headlights will swivel, which helps illuminate the road when going around curves. Adaptive headlights improve a drivers’ reaction times by about a third of a second, just enough to avoid hitting a parked car or animal on a dark road.


Lane departure warning (LDW) and assist LDW


These systems use a camera, along with various sensors, to identify lane markers and monitor your distance from them. If you stray over the line without signaling, you’ll hear a warning tone, an LDW warning in the instrument panel or perhaps a physical alert like a vibration in the steering wheel or seat.


Lane departure warning does not provide a warning to help avoid a cash unless it detects the lane markings. More advanced “lane keeping assist” (LKA) systems selectively apply brakes or nudge the steering to guide you back if you’re wandering.



Automatic park assist


The system will identify a parallel or perpendicular parking space your car can fit into. Once found, the system steers the car into the space; some can also exit from parallel parking

spaces. The driver still does the braking and has to follow commands from the system.



Rear cameras and parking assist



Rear-view cameras will be mandatory with the 2018 model year. They can help prevent a back-over accident, such as hitting a child who wanders behind your car. Parking assist sensor systems notify you with progressively louder and quicker beeps as you close in on an obstacle.


  1. View displayed by the camera.
  2. Corners of the rear bumper.


Knowing what collision-avoidance systems a vehicle may have and what they are designed to do is within the realm of the private investigator. Due to the growing list of collision-avoidance systems the investigator must consider this advanced technology as part of their investigation. By researching the vehicle involved, the investigator can determine the type of systems a vehicle is equipped with. Understanding what the systems are designed to do can assist the investigator in discovering other factors involved in a traffic accident. These questions can become important for the client or the attorney.

Questions for the investigator to consider include:

  • What is the vehicle equipped with?
  • What is the system designed to do?
  • Did the system work properly?
  • Was the driver provided a warning of the potential hazard?
  • Did the driver respond to that warning?

The investigator can check the IIHS website: www.iihs.org/iihs/ratings/crash-avoidance-features or contact the local vehicle manufacture dealership to get information about the systems a vehicle may have and what they are supposed to do.  


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Our second article has been posted on PI Now. https://www.pinow.com/articles/2349/accident-investigations-vehicle-lamp-examinations


View our latest article on tire marks and their use in accident investigations at: https://www.pinow.com/articles/2399/tire-marks-their-role-in-accident-reconstruction-investigations

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