What Are Yaw Marks? How They're Used In Car Accident Investigations

‍What are Yaw Marks?

Yaw marks are a type of skid marks that are made by a tire that is sliding or turning sideways. The movement is parallel to the tank wheel’s axle. These marks are also called critical speed scuff marks and curved.

Although most people confuse yaw marks with skid marks, the former is characterised by a tire rolling and side slipping at one time. That means the vehicle is likely out of control, rotating around its centre of mass and not travelling in the direction the driver intended.

Most yaw marks are initiated by steering input. For example, if you’re driving too fast into a corner, that will create a set of yaw marks.

Unlike other tire marks, yaw marks have distinct streaks or stripes when the sidewall is drugged over the road.  Yaw marks are aligned in the spin direction, the reason they are parallel to the car’s axle.

A yawing motion happens when the vehicle loses traction while rounding a curve. The motion could happen with braking, spinning, or rolling motion. It depends on road conditions, the driver’s actions, and other things.

Experts refer to yaw marks as any tire marks left by yawing motion without braking.

Tire yaw marks can be black marks left on asphalt by rubber heat and transfer, marks keft by rubber transfer and an erasure effect on concrete, or marks left by cleaning or ploughing the surface on mud gravel, snow, or cement.

Some of the common characteristics of yaw marks include:

• Starting faint and becoming bold at the end
• Becoming wide than the tread width
• The outside mark on the convex side of the yaw mark is darkest, and the car's rear tire is on the outside. curve
• Striations within the tire mark not parallel to the mark’s direction
• A pattern that forms an arc with marks crossing each other
• Marks left by the outside edge of the tire sidewall
• Marks that start thinner than the tread width

How are Yaw Marks Used in Car Accident Investigations?

Tire marks have over the years been used in car accident investigations.

Identifying tire marks is a crucial aspect of any accident investigation. A specific action of the vehicle produces a tire mark, and this is what tells the police above what the driver attempted to do before/after a collision or what the driver did to contribute to the accident.

Police use yaw and skid marks to determine the speed with enough accuracy.

The investigator studies the area of impact or a point of impact using these tire marks. They may come up with a conclusion when examining a suspect's tire and a crime scene impression. That can only happen when the two match in dimension, design, condition of wear, and other features.

A car travels in a decreasing spiral to rest when in a yawing motion. That means that the bigger the arc radius, the faster the vehicle. It also tells the investigator that the car is rolling to rest and was not accelerating or braking. The tire marks will be thinner throughout the yaw the greater the vehicle’s speed.

For example, specific yaw marks can tell the investigator that the driver may have been going very fast to negotiate the curve. The driver turns the steering wheel while braking to avoid going off the road. That will cause the car to get into centrifugal yaw, where the vehicle's rear slides outside the skid.

In a case where a driver was speeding and hit the brakes at the time of an impending crash, that creates lengthy yaw marks on the road. The wheels lock up, and the vehicle skid because of the forward momentum.

An accident reconstruction expert during the investigation measures the length of these marks and compares them to the amount of damage. That can tell how fast the driver was during the crash. With this information, the claim can provide evidence that the accused had exceeded a specific speed limit when the accident occurred.

Can Yaw Marks Determine How a Crash Happened?

Although yaw marks may not provide enough proof of how a crash happened, these marks can provide supporting evidence.

Track impressions can help determine the tire size, style, and brand as manufacturers produce different tire patterns. An investigator can determine crime-related evidence using tire track impressions by matching through searchable databases.

Yaw marks show that the driver was broadsided or that a spinout occurred. These curved tire marks can also show that the driver was accelerating too fast or speeding on a slippery road and was fishtailed.

A car can do different things during or after yaw like:

• Form another yaw if the driver is oversteering
• Rollover if on a soft surface
• Come to rest backwards from the original direction of travel
• Strike another item like a pole or a curb, resulting in a rollover or change of course
• The driver may also regain control