Validation of the Circular Trajectory Assumption in Critical Speed

In a maneuver called a critical speed yaw, which occurs when a driver makes a dramatic steering input, the force required to turn the vehicle in the path requested exceeds the force that the tires are capable of generating. As a result, the vehicle turns in a path primarily defined by available friction and the vehicle's velocity. Accident reconstructionists often use the critical speed model to determine vehicle speeds. This model assumes that the vehicle's center of mass travels in a circular arc when in a critical speed yaw. This study investigates the validity of this assumption by comparing the results obtained by manually measuring the tire marks, assuming them parallel to the center of mass path, and fitting a polynomial. Findings indicate that the circular arc assumption is reasonably accurate. Results also indicate that 2nd order polynomial is a good approximation to describe the tire mark trajectory. The 3rd order polynomial might provide more accurate estimation for higher speed using the radius of curvature at x=0. Using the radius of curvature at midpoint of the trajectory provides results similar to the conventional method of measuring a chord and middle ordinate and calculating the radius.

Language

  • English

Media Info

  • Media Type: Print
  • Features: Figures; References; Tables;
  • Pagination: pp 129-133
  • Monograph Title: Accident Reconstruction 2005

Subject/Index Terms

Filing Info

  • Accession Number: 01005757
  • Record Type: Publication
  • ISBN: 0768015758
  • Files: TRIS
  • Created Date: Oct 4 2005 10:43AM