This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
Challenging the Critical Speed Formula In Light Of the Daubert Decision
Technical Paper
2005-01-3141
ISSN: 0148-7191, e-ISSN: 2688-3627
Annotation ability available
Sector:
Event:
Language:
English
Abstract
Yaw marks are often observed at the scene of an accident when a car spins out of control on a curve. Police investigators measure the radius of these marks and conduct skid tests at the scene to determine the friction, or drag factor, on that road surface. The radius and friction values are then plugged into the Critical Speed Formula, or CSF, to compute the car's speed. Such estimates may later form the basis of the officer's expert testimony for speed related prosecutions, including criminally negligent homicide. The CSF is derived from a more generalized equation that balances cornering force with inertia. But the CSF is too simplistic to account for all the variables that affect a cornering vehicle, and the methods normally used to employ it are not valid. By default, the braking friction value from the police cruiser is substituted into the equation for the cornering force limit of the crashed car, because cornering friction is either too dangerous or impractical to obtain at the scene. The car that caused the yaw marks may be too damaged to drive - the best evidence destroyed - and the roadway not wide enough to conduct a skid pad test. The operant hypothesis is that the braking friction limit of every test car is equal to the cornering friction limit of any car on the road.
Stated mathematically:
Analysis of independent, real world data shows the potential for error using such methods exceeds 41%.
Recommended Content
| Technical Paper | An Analytical Assessment of the Critical Speed Formula |
| Technical Paper | Formulas for Estimating Vehicle Critical Speed From Yaw Marks - A Review |
| Technical Paper | Relationships Between Pre-Skidding and Pre-Braking Speed |
Authors
Citation
Fischer, W., "Challenging the Critical Speed Formula In Light Of the Daubert Decision," SAE Technical Paper 2005-01-3141, 2005, https://doi.org/10.4271/2005-01-3141.Also In
References
- Badger, Joseph E. “Different Methods for Determining Radii,” Accident Reconstruction Journal July Aug 1990 12 13
- Baker, J. Stannard “ Traffic Accident Investigation Manual,” Evanston Traffic Institute Northwestern University 1975
- Baxter, Albert T. “An Examination of the Critical Speed Problem” Accident Reconstruction Journal Nov Dec. 1993 23 29
- Bellion, Peter “Project Y.A.M. (Yaw Analysis Methodology) Vehicle Testing and Findings” Victoria Police, Accident Investigation Section Society of Automotive Engineers Technical Paper Series 0955 1997 171 209
- Brandt, Bill. “A.B.S. Increases Stopping Distance in Braking/Evasive Maneuver,” Accident Reconstruction Journal March April 1994 41 42
- Brach, Raymond M. “An Analytical Assessment of the Critical speed Formula,” Society of Automotive Engineers Technical Paper Series 0957 1997 241 249
- Brach, Raymond M. Russell A. Smith “Tire Forces and Simulation of Vehicle Trajectories,” Accident Reconstruction Journal Nov Dec 1991 20 21
- Collins, James C. Accident Reconstruction Charles C. Thomas 1979
- Craig, Victor “Maryland State Police Skid Test Data,” Accident Reconstruction Journal Jan Feb 1989 10 11
- Craig, Victor “Performance Tests of Various Tires on Snow,” Accident Investigation Quarterly Winter 2000 37
- Dickerson, Charles P. et. al. “Evaluation of Vehicle Velocity Predictions Using the Critical Speed Formula,” Society of Automotive Engineers Technical Paper Series 0137 1995 81 89
- Fischer, Grahme “Yaw Marks and Critical Speed on Curves,” NYSTARS Newsletter Dec 1999 4 6
- Fischer Grahme Wood “Vehicle and Tire Dynamics During Braking and Cornering,” NYSTARS Newsletter May 2000 12 13
- Fricke, Lynn B. Traffic Accident Reconstruction Evanston Northwestern University Traffic Institute 1990
- Gillespie, Thomas D. Fundamentals of Vehicle Dynamics Society of Automotive Engineers, Inc. 1992
- Halvorsen, James R. “Describing ‘Yaw Marks’ to the Jury,” Accident Investigation Quarterly Winter 1998 38
- Heydinger, Gary et.al. “Measured Vehicle Inertial Parameters - NHTSA'S Data Through November 1998,” Society of Automotive Engineers Technical Paper Series 01-1336 1999
- Irwin, Jack Swinson, Derek “A Demonstration of Car Braking Instabilities,” Accident Reconstruction Journal Jan Feb 1993 42 43
- Lambourn, Richard F. “Braking and Cornering Effects with and without Anti-Lock Brakes,” Society of Automotive Engineers Technical Paper Series 0723 1994 155 161
- Limpert, Rudolph Motor Vehicle Accident Reconstruction and Cause Analysis The Michie Company Second 1978
- Martinez, Luis “Estimating Speed from Yawmarks - An Empirical Study,” Accident Reconstruction Journal May June 1993 48
- McCaffrey, Michael T “Critical Speed ‘Yaw’ Computer Analysis - Metric & USA Units,” Accident Reconstruction Journal July Aug 1992 56
- McIsaac, B.R. Grage J.C.W. “Coefficient of Friction Tests at Varying Tire Inflation Pressures Accident Reconstruction Journal Jan Feb 1993 40 48
- Nelson, Wilton “Use of a Jig to Aid Yaw Mark Evaluation,” Accident Reconstruction Journal Mar April 1990 12 13
- Norsemeter “Un Update on Road Grip Friction - The Frictional behaviour of the Interface between Road pavement and Automotive Tyre,” 1st IXth PIARC Winter Congress Seefeld 25 March 1994
- Reizes, Haim The Mechanics of Vehicle Collisions Charles C. Thomas 1973
- Shelton, Thomas Craig, Victor “Translational Deceleration from Vehicle Sideslip,” Accident Reconstruction Journal Jan-Feb. 1995 43 51
- Shelton, Thomas “Validation of the Estimation of Speed from Critical Speed Scuffmarks,” Accident Reconstruction Journal Jan Feb 1995 37 40
- Sledge, Nathaniel Marshek Kurt “Formulas for Estimating Vehicle Critical Speed from Yaw Marks - A Review,” Society of Automotive Engineers Technical Paper Series 1147 1997 1 10
- Smith, Nicholas D. “Understanding Parameters Influencing Tire Modeling,” Colorado State University 2004 Formula SAE Platform
- Strandberg, Lennart “Winter Braking Tests with 66 Drivers, Different Tyres and Disconnectable ABS,” Society of Accident Reconstructionists Winter 2005 22 34