crash reconstruction: a complete step-by-step procedure...conclusions 1. crown victoria was...
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Crash Reconstruction:
A Complete Step-by-Step Procedure
Terry D. Day, P.E.
Engineering Dynamics Corporation
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IntersectionCrash Reconstruction
fromCradle
toGrave
Engineering Dynamics Corporation
Instructor: Terry D. Day, P.E.
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OutlineOutline• Description of Crash• Required Physical Data• Police Accident Report• Data Development• Data Reduction• Analysis• Conclusions• Discussion
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Description of CrashDescription of Crash• Not a Real Crash• “MSU”
GOAL:• Present a Procedure• Not to Present a Case Study
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Description of CrashDescription of Crash• Small, Rural Town• 90-degree Intersection• Relatively Level• 4 Lanes (2 in each direction)• 2 Vehicles (Passenger Cars)• Stop Signs
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Questions to AddressQuestions to Address• Cause
Vehicle Speeds? Inattention? Failing to Stop?
• Avoidability What If…?
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Required Physical DataRequired Physical Data• Impact Speed
Position at Impact Position at Rest Path between Impact and Rest Wheel Lockups (Drag Factor) Damage Profile
− Required for Collinear Collision− Optional for Oblique Collision
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Required Physical DataRequired Physical Data• Begin Braking Speed
Impact Speed (previous slide) Position at Begin Braking
− 13 ft of faint tire marks (ABS) Pre-impact Wheel Lockups (drag factor)
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Police Accident ReportPolice Accident Report• Basic Scene Information
General Location Rest Positions Crash-related Artifacts
− Skidmarks− Gouge marks− Glass…
• Basic Vehicle Information Make/Model/Year
• Witness Statements Limited Emphasis
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Vehicle InspectionVehicle Inspection• Make/Model/Year/Body Style• Dimensions/Inertias• Wheel Damage/Lockups• Damage Profiles• Documentation
Photographs Other Notes/Observations
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Site InspectionSite Inspection• Location/Direction• Street Dimensions• Skid/Scuff/Gouge Locations• Surface Irregularities• Survey• Documentation
Origin Photographs Other Notes/Observations
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Data ReductionData Reduction• Vehicle Models• Environment Model• Crash-related Artifacts
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Vehicle ModelVehicle Model• Dimensions
Exterior Wheel Locations wrt CG
• Weight/Rotational Inertia• Tires
Friction Cornering Stiffness
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Environment ModelEnvironment Model• To Scale!• Driving Surfaces
with Skids/Scuffs/Gouges• Sidewalks• Buildings (vision obstructions)• Stop Signs
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AnalysisAnalysis• Reconstruction
Speed Estimates• Simulation
Confirm Speed Estimates Time-Distance Study
• Perception/Reaction Time• Cause/Avoidability
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ReconstructionReconstruction• Damage Analysis
Crown Victoria Only
Result:• Speed Estimate
Impact with Brick Building
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ReconstructionReconstruction• Position at Begin Braking
Crown Victoria Only• Positions at Impact• Positions at Rest• Wheel Lockups
Results:• Speed Estimates
Begin Braking Impact Separation
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SimulationSimulation• Initial Positions• Driver Controls
Steering Braking Throttle
• Wheel Impact Damage
Results:• Confirmation of Initial Speeds• Time-Distance Study
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Perception/Reaction TimePerception/Reaction Time• Initial Visibility
Position Time
• Begin Braking Position Time
• Difference is Maximum Perception/Reaction Time
TP/R (max) = TBegin Braking – TInitial Visibility
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Result…Result…
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Result…Result…• Initial Visibility
Time = 1.32 sec Position (to be used later)
− Crown Vic X = -73.2, Y = 20.0− Impala X = 18.0, Y = 97.4
• Begin Braking Time = 2.52 sec
• So:TP/R (max) = 2.52 – 1.32 = 1.20 sec
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ObservationsObservations• Typical Perception/Reaction times
0.75 sec for Reaction Time Test 1.25 sec, min (lots of sources) 2.50 sec, max (AASHTO)
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ConclusionConclusion• Inattention Not a Factor
Also…• Time at Begin Steering = 1.52
Driver began steering almost instantly (0.20 sec after initial vis) Driver was probably watching for cross traffic
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Was Speed a Factor?Was Speed a Factor?• Crown Victoria Speed = 40 mph• Speed Limit = 25 mph• To Find Answer:
Position vehicles at initial visibility (from earlier result) Crown Vic X = -73.2, Y = 20.0 Impala X = 18.0, Y = 97.4
Reduce speed from 40 to 25 No steering/braking Re-execute
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Result …Result …
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Result …Result …• At 25 mph, Crown Victoria passes behind Impala• Misses by 25 ft
Speed was a factor
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Additional InformationAdditional Information• Did Impala Stop?• To Find Answer:
Position vehicle at stop line Accelerate at WOT to impact point Compare speed with impact speed
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Result …Result …
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Result …Result …• Speed = 24 mph
(less than impact speed, 35 mph) Impala did not stop at stop sign
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ConclusionsConclusions1. Crown Victoria was exceeding the speed limit2. Collision does not occur if Crown Victoria obeys
the speed limit3. Although collision is avoided, it is a near-miss4. Impala did not have sufficient room to pull out
safely5. Impala did not stop
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Discussion/QuestionsDiscussion/Questions
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Engineering Dynamics Corporation
Thank You
IntersectionCrash Reconstruction
fromCradle
toGrave