Yaw Mark
Definition
A curved, striated tyre impression produced when a vehicle slides at an angle to its direction of travel during a steered or yawing skid; the radius of curvature provides an independent speed estimate via v = sqrt(mu g r).
- Mark pattern
- Curved, striated tyre impression
- Typical cause
- Cornering at the limit of grip or steered skid
- Speed calculation method
- Radius of curvature formula: v = sqrt(mu g r)
Common questions
What is a yaw mark and how is it different from a skid mark?+
A yaw mark is a curved, striated tyre impression left when a vehicle slides at an angle to its direction of travel, typically while cornering or during a steered skid. Unlike a braking skid mark (which shows wheels locked in a straight line), a yaw mark curves because the vehicle is moving sideways, not because the driver is stopping.
Can you calculate the speed of a vehicle from a yaw mark?+
Yes. The radius of curvature of the yaw mark allows you to estimate the vehicle's speed using the formula v = sqrt(mu g r), where mu is the coefficient of friction, g is gravitational acceleration, and r is the radius. The chord and middle ordinate (the arc's width and height) provide additional geometric data to refine the speed calculation.
Why do yaw marks appear curved?+
Yaw marks curve because the vehicle is sliding sideways at an angle to its direction of travel. The tyre leaves a curved impression as it moves through this angled slide, which is why the mark traces an arc rather than a straight line.
Related terms
- Braking Mark
- A continuous black skid produced when wheels are fully locked under braking and the tyre slides on the road. Length plus drag...
- Coefficient of Kinetic Friction (Mu)
- The dimensionless ratio of the sliding friction force to the normal force between a tyre and the road; typically 0.55-0.70 for dry...
- Coefficient of Restitution (E)
- The ratio of the relative velocity of separation to the relative velocity of approach in a collision; e = 0 for perfectly...
- Daubert Standard
- The US federal evidentiary standard (Daubert v. Merrell Dow Pharmaceuticals, 1993) requiring that expert testimony be based on scientifically valid methods with...
- Drag Factor (μ)
- The effective coefficient of friction between the tyre and the road surface during a braking event. Used in the skid-mark speed formula....
- EDR (Event Data Recorder)
- An onboard module that records pre-crash speed, throttle, brake application, steering input and seatbelt status for several seconds before airbag deployment. The...
- Energy-Equivalent Speed (EES / Delta-V)
- The SAE J2080 metric quantifying the kinetic energy absorbed by vehicle crush deformation, expressed as the speed change equivalent; used in the...
- Event Data Recorder (EDR)
- An onboard module that records pre-crash vehicle kinematics (speed, throttle, brake, steering) in the seconds before airbag deployment; governed by SAE J1698...
- Gouge Mark
- A scrape or trench cut into the pavement when a metal component (frame, axle, undercarriage) strikes the road during or after impact....
- Head-Throw Distance (HTD)
- The horizontal distance from the vehicle's front bumper contact zone to the final rest position of the pedestrian's head; used in the...
- IRTE
- Institute of Road Traffic Engineers (UK); publishes the Forensic Collision Investigation manual that governs police and expert-witness reconstruction methodology in England and...
- Momentum Conservation
- In the absence of external horizontal impulses, the total linear momentum of a two-vehicle collision system (sum of mass times velocity for...
Explained in these topics
- Accident Investigation: Skid Marks, Collision and Hit-and-RunA curved striated mark left when a vehicle cornering at the limit of grip slides sideways. The chord and middle ordinate of the arc allow speed-at-yaw to be co...
- Accident Reconstruction Physics: Velocity, Momentum and Skid MarksA curved, striated tyre impression produced when a vehicle slides at an angle to its direction of travel during a steered or yawing skid; the radius of curvatu...