Effect of Driver Response on Vehicle Control Loss during a Rear Tire Tread Separation

Effect of Driver Response on Vehicle Control Loss during aRear Tire Tread Separation Wilson Consulting, LLC

Problem Statement Q: What is the principal issue? A: InjuriesQ: How do the injuries occur? A: Rollovers, 3/30 RuleQ: How do the rollovers occur? A: Loss of ControlQ: How does loss of control occur? A: Drift Off Road/Missed Curve (39%)Tread Separation (25%) Accident Avoidance (18%) Other (17%) Wilson Consulting, LLC

Overview • Examples of Real-World Tread Separation Accidents • Factors Affecting Loss of Control • Human Factors Considerations Wilson Consulting, LLC

Examples of Real-World Tread Separation Events Wilson Consulting, LLC

Partial Tread Separation/Air Out Tread Partially Attached Carcass Blow Out

Accident Scene Evidence Partial Tread Separation/Air Out Left Rear Left Front Tire/Rim Skips

Accident Scene EvidenceRim Gouge & Tire Marks – Tread Separation/Air Out Left Front Left Rear

Accident Scene Evidence Rim Gouge &Tire Marks – Tread Separation/Air Out Right Front Left Rear Right Rear

Accident Scene Evidence Start of Pre-Roll Yaw Marks – Tread Separation

Accident Scene Evidence Pre-Roll Yaw Marks – Tread Sep Left Rear Left Front Right Rear Right Front

Accident Scene EvidenceEnd of Tire Marks – Tread Sep Left Rear Left Front

Factors Affecting Loss of ControlDuring Tread Separation • Vehicle Characteristics • Vehicle Speed • Driver Response • Driver Expectancy • Prior Experience with Tread Separations Source: NHTSA Report “Investigation of Driver Reactions to Tread Separation Scenarios in the National Advanced Driving Simulator (NADS)” Wilson Consulting, LLC

Circle Test at Low Speed Ackerman Steer Angle is the Amount of Steer Required To Drive The Vehicle in the Prescribed Circular Path (usually 100 ft radius) Ackerman Steer Angle CircularPath Ackerman Steer Angle • Low Speed • Minimal Lateral Acceleration • No Tire Scrub

At-Limit Understeer Increased Speed Requires Increased Steer to Maintain Prescribed Circular Path Ackerman Steer Additional Steer AckermanSteer Additional Steer • Increased Speed • Increased Steer • Increased Lateral Acceleration • Understeer Gradient = Additional Steer/Increase in Lateral Acceleration

Effect of Understeer Gradient on Loss of Control Drivers Are More Likely to Maintain Control in a Vehicle with High Understeer Gradient Source: NHTSA Report “Investigation of Driver Reactions to Tread Separation Scenarios in the National Advanced Driving Simulator (NADS)” Wilson Consulting, LLC

Vehicle Understeer Gradient Vehicle’s Understeer Gradient and Inherent Directional Stability Are Drastically Reduced by a Rear Tire Tread Separation

Other Vehicle Characteristics that Adversely Affect Loss of Control • Move CG Rearward* • Reduces Understeer • Lateral Load Transfer* • Reduces Understeer • Increase CG Height* • Reduces Rollover Stability • Increases Lateral Load Transfer • Low Roll Stiffness • Reduces Effective Trackwidth • Increases Lateral Load Transfer • Front-to-Rear Roll Stiffness Ratio • Reduces Understeer * Effect Caused by Passenger and Cargo Loading

Effect of Vehicle Speed on Loss of Control • Drivers More Likely to Experience Loss of Control at Higher Speeds • In NHTSA Study, Speeds Ranged from 71-81 mph at Time of Tread Separation Source: NHTSA Report “Investigation of Driver Reactions to Tread Separation Scenarios in the National Advanced Driving Simulator (NADS)” Wilson Consulting, LLC

Initial Driver Response to Tread Separation (Vehicles 1-3) Steering Was Initial Reaction for Drivers Who Were Not Expecting Tread Separation Initial Response of Drivers Steering or Braking Source: NHTSA Report “Investigation of Driver Reactions to Tread Separation Scenarios in the National Advanced Driving Simulator (NADS)” Driver Responses with Experimenter Interaction Not Included Wilson Consulting, LLC

Effect of Driver Expectancy on Loss of ControlAbility to Maintain Control of Vehicle Strongly Associated with Expectancy Vehicle 1 Percentage of Drivers that Experienced Vehicle Loss of Control Source: NHTSA Report “Investigation of Driver Reactions to Tread Separation Scenarios in the National Advanced Driving Simulator (NADS)” Wilson Consulting, LLC

Initial Driver Response to Tread Separation (Vehicles 1-3) • Expectancy/Experience Improved Likelihood of Maintaining Control Whether Initial Response was Steering or Braking Source: NHTSA Report “Investigation of Driver Reactions to Tread Separation Scenarios in the National Advanced Driving Simulator (NADS)” Driver Responses with Experimenter Interaction Not Included Wilson Consulting, LLC

Factors Having Minimal Effect on Loss of Control During Tread Separation • Written Instructions on Maintaining Vehicle Control During a Tread Separation • Driver Age • Right vs. Left Tread Separation Source: NHTSA Report “Investigation of Driver Reactions to Tread Separation Scenarios in the National Advanced Driving Simulator (NADS)” Wilson Consulting, LLC

Human Factors that AffectDriver’s Ability to Maintain Vehicle Control During a Tread Separation Event • Expectancy • Prior Tread Separation Experience • Perception-Response Time Wilson Consulting, LLC

Comparison of “Tread Separation” Tests • Comparison of Actual Tread Separation Test to a Single-Wheel Braking Test • Single-Wheel Braking Test Simulates Vehicle Motion (Yaw and Yaw Rate) Caused by Tread Separation Event Source: SAE Paper 2007-1-0836, Tandy, Carr, Liebbe, et al. Wilson Consulting, LLC

Wilson Consulting, LLC

Test Driver Response to Actual TreadSeparation Test • Test Driver Expecting Tread Separation and Subsequent Clockwise Rotation • Test Driver’s Stimulus for Initial Reaction (Steer Left) is Noise/Vibration Caused by Tread Separation, not Vehicle’s Clockwise Motion • Test Driver Steers Left Simultaneously as Vehicle Starts to Rotate Clockwise Wilson Consulting, LLC

Perception-Response Process • Detection – Sensory Stimulus that Allows Driver to Become Aware of a Potential Hazard • Identification – Driver Must Acquire Sufficient Information to Decide What Response, If Any, is Appropriate • Decision – Typically, Driver Decision is to Change Direction, Change Speed or Both • Response – Driver’s Brain Issues Instructions to Appropriate Muscle Groups to Carry Out Intended Action Olson, Farber, Forensic Aspects of Driver Perception and Response, Second Edition, 2003

Test Driver’s Perception-Response Process • Detection – Driver Perceives Tread Separation by Noise and Vibration Caused by Tread-to-Vehicle Interaction • Identification – Test Driver Need Not Identify Perceived Hazard Because Driver is Expecting Tread Separation • Decision – Test Driver Response Already Pre-Determined Because Driver is Expecting Tread Separation and Driver Has Experience Handling Tread Separations • Response – Movement of Steering Wheel By Driver Wilson Consulting, LLC

Test Driver’s Perception-Response Process • Detection – Driver Perceives Tread Separation by Noise and Vibration Caused by Tread-to-Vehicle Interaction • Response – Movement of Steering Wheel By Driver Expectationof Tread Separation and Prior Experience with Tread Separations Eliminates Step 2 (Identification) and Step 3 (Decision) from P-R Process Wilson Consulting, LLC

Test Driver Response to Actual TreadSeparation Test • Test Driver’s Response Time is Unrealistically Short (0.4 sec) When Compared to Response Times in Real-World, Unexpected Tread Separations • Test Driver’s Amount of Steer is Inconsistent with Typical Emergency Steer Inputs (Test Driver Experienced with Tread Separations) • Even with Unrealistically Fast Response Time, Vehicle Still Diverts Entirely From Original Lane of Travel and Never Returns to Original Lane of Travel Wilson Consulting, LLC

Driver’s Perception-Response Process in Real-World Tread Separation Event (Part 1) • Detection – Driver Detects Tread Separation by Noise and Vibration Caused by Tread-to-Vehicle Interaction • Identification – Most Drivers Unable to Identify that Tread is Separating from Rear Tire Based on Noise/Vibration Unable to Proceed to Step 3 (Decision) Because Perceived Hazard Not Identified Wilson Consulting, LLC

Driver’s Perception-Response Process in Real-World Tread Separation Event (Part 2, P-R Start Over) • Detection – Driver Perceives Unexpected Change in Vehicle Heading • Identification – Without Driver Input, Vehicle Will Exit Roadway • Decision – Steer To Avoid Leaving Roadway • Response – Movement of Steering Wheel by Driver Wilson Consulting, LLC

Driver Response Time to Single-Wheel Braking Test Similar to Real-World Driver Response • Driver’s Response Time is 1.2 to 1.5 Seconds After Start of Vehicle’s Clockwise Rotation • Driver’s Response Time is 1.6 to 1.9 Seconds After Start of Noise/Vibration from Tread Separation • In Real–World, Unexpected Tread Separation Events, Drivers Steer in Response to the Vehicle’s Unexpected Change in Heading Caused by Tread Separation Wilson Consulting, LLC

Effect of Driver Response Time on Vehicle Loss of Control * Achieved Loss of Control ** Emergency Steer Inputs

Braking Wilson Consulting, LLC

Effect of Initial Driver Response to Tread Separation on Loss of Control (Vehicles 1–3) • Drivers More Likely to Maintain Control if Braking was Initial Response Source: NHTSA Report “Investigation of Driver Reactions to Tread Separation Scenarios in the National Advanced Driving Simulator (NADS)” Driver Responses with Experimenter Interaction Not Included Wilson Consulting, LLC

NHTSA Study Demonstrates Favorable Results if Braking is Initial Response to Tread Separation Event However, When conducting test of 15-passenger vans subject to rear tire tread separation/air-outs, “STL and Michelin determined that braking after the blow out would be dangerous, and the [professional] driver stated that he would be uncomfortable conducting the test if he were required to brake.” (NTSB /HAR-03/03, PB2003-916203, July 15, 2003) Wilson Consulting, LLC

Conclusions Wilson Consulting, LLC

Vehicle Can Experience Loss of Control Solely as a Consequence of Tread Separation. • Driver’s Initial Response Was to Steer in Unexpected Tread Separation Events. • Driver Expectancy Strongly Affects Ability to Maintain Control. • Driver Expectancy Significantly Reduces Perception-Response Time. Wilson Consulting, LLC

Vehicle’s Rotation and Yaw Rate Increase as Driver’s Response Time Increases. • Response of Professional Drivers in Expected Tread Separation Tests Do Not Accurately Reflect Reponses of Drivers in Unexpected Real-World Tread Separation Events. • Drivers with Prior Tread Separation Experience Can Anticipate Vehicle’s Motion Thereby Minimizing Vehicle’s Yaw and Yaw Rate.

Effect of Driver Response on Vehicle Control Loss during a Rear Tire Tread Separation