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Dr Ciaran SimmsDr Ciaran Simms
PEDESTRIAN KINEMATICS AND INJURIES IN COLLISIONS WITH VEHICLES
REAL WORLD PEDESTRIAN ACCIDENT
REAL WORLD PEDESTRIAN ACCIDENT
REAL WORLD PEDESTRIAN ACCIDENT
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PEDESTRIANS AND CYCLISTS – VULNERABLE – NO PROTECTION
IRELAND 2005 – ROAD COLLISION FACTS IRELAND 2005
18% OF FATALIIES (74 DEATHS)
10% OF INJURIES
ROAD DEATHS IN EUROPE PER 100000
0 5 10 15 20 25
United Kingdom
Sw eden
Finland
Ireland
Austria
Spain
Luxembourg
Portugal
http://www.statistics.gov.uk/STATBASE/Expodata/Spreadsheets/D7254.xls
PEDESTRIAN VEHICLE IMPACTS
AT COLLISION SPEEDS LESS THAN 20KM/H, PEDESTRIANS USUALLY SUSTAIN ONLY MINOR INJURIES.
BUT AT SPEEDS ABOVE 45KM/H, COLLISIONS WITH PEDESTRIANS ARE MOSTLY FATAL [WOOD, 1990] [OTTE, 1999].
THE REASON FOR THE DOMINANCE OF SPEED IS THAT THE COLLISION ENERGY INCREASES WITH THE SQUARE OF THE IMPACT SPEED
2..21 vMEKINETIC =
PEDESTRIAN FATALITIES VERSUS IMPACT SPEED
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URBAN SPEED LIMITS: REDUCING SPEED
LIMITS TO 50 KM/H FROM 60KM/H
DEATH RATE OF ADULT
PEDESTRIANS 30% LOWER
AUSTRALIAN STUDY: EFFECTOF REDUCING IMPACT SPEED
ANALYSIS OF PEDESTRIAN KINEMATICS
YIELDS INSIGHTS –
IMPACT LOCATIONS ON VEHICLE
IMPACT LOCATIONS ON THE BODY
VEHICLE SPEED FOR CRASH RECONSTRUCTION
CLASSIFICATION:
1. WRAP PROJECTION2. FENDER VAULT3. FORWARD PROJECTION4. ROOF VAULT
WRAP PROJECTION
FENDER VAULT
REAL WORLD WRAP PROJECTION
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REAL WORLD WRAP PROJECTION
FORWARD PROJECTION
ROOF VAULT
REAL WORLD FORWARD PROJECTION
PEDESTRIAN IMPACT SIMULATION: WRAP PROJECTION
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LOWER LEG AND HEADKNEE PELVIS
CAUSED BYBUMPER AND BONNET & WINDSCREEN STIFFNESSIMPACT WITH THE GROUND
PEDESTRIAN INJURIESPEDESTRIAN IMPACT SIMULATION:
WRAP PROJECTION
PEDESTRIAN INJURIES ARE COMPLEX: MANY INJURIES CAN OCCUR IN ONE COLLISION
OTTE, IRCOBI, 2005
INTRODUCTION OF REGULATORY TESTS
http://www1.tpgi.com.au/users/mpaine/ped_veh.html
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IMPROVEMENTS IN KNEE PROTECTION THROUGH VEHICLE DESIGN
OTTE, IRCOBI, 2005
EFFECT OF DESIGN IMPROVEMENTSON KNEE INJURIES
OTTE, IRCOBI, 2005
ACCIDENT RECONSTRUCTION: VEHICLE SPEED ESTIMATION FROM THROW DISTANCE
ACCIDENT INVESTIGATION TECHNIQUES
CORRELATION OF INJURIES WITH IMPACT SPEED
ABS REDUCES TYRE SKID
LEGAL CASES
SEARLE’S PARTICLE MODEL [IMECHE, 1993]
SLIDE/ROLL/BOUNCE DISTANCE NOT TRIVIAL –OFTEN > FLIGHT
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µ - coefficient of retardationM- mass of pedestrianS - distance to restH - height drop of cg to restU, v – horiz & vert comp launch velocityLaunch angle generally unknown
( ) Hg2vuS2
µ+µµ+
=
HOW TO RELATE LAUNCH VELOCITY TO VEHICLE SPEED?
SEARLE’S PARTICLE MODEL UNCERTAINTY IS MAJOR FACTOR
WHY NOT SAY: HERE’S THE MASS, HERE’S THE FRICTION ETC,-HENCE THE SPEED - BUT THAT DOESN’T WORK IN PRACTICE
MONTE CARLO SIMULATION
REQUIRE PARAMETERS DISTRIBUTION
NORMAL DISTRIBUTIONS FOR MC, MP, µ:
FORWARD PROJECTION
bouncerollslideoverfallingimpacttotal SSSS //++= −
[ ] colPv
vproj Ve
MMMV ++
= 1
impactprojimpact tVS ×=
DISTANCE CARRIED IN INITIAL IMPACT
MOMENTUM AND RESTITUTION
PROJECTION VELOCITY COLLISION VELOCITY
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RxM p µ−=..
FALLING OVER DISTANCE
RgMyM pp −=..
( ) ( )φµφφ cossin..
2 RhhRkM p +=
( ) ( )φφφφ sincos..2...hhy +
=CONSTRAINT:FEET IN CONTACT
WITH THE GROUND
3 DOF
NUMERICAL INTEGRATION OF THIS SYSTEMTO YIELD DISTANCE TRAVELLED IN FALLING OVER
EQUATIONS OF MOTION FOR PLANAR SYSTEM
( ) )90()90(
.
_ ==
−
= φ
φ
µ tvt
fproj VxV
DISTANCE TRAVELLED IN SLIDE/ROLL/BOUNCE TO REST
gV
S fprojbouncerollslide µ2
2_
// =
EQUATION OF UNIFORM DECELERATION
SPEED LOSS DUE TO IMPACT WHEN CG HITS THE GROUND
FORWARD PROJECTION: MODEL RESULTS
WOOD, SIMMS AND WALSH, IMECHE 2004
WRAP PROJECTION: SIMILAR BASIS FOLLOWED
TOTAL THROW DISTANCE IS COMBINATION OF INITIAL CONTACT, FLIGHT AND SLIDE TO REST PHASES
MOVEMENT MORE COMPLEX DUE TO ROTATION ONTO THE BONNET AND SECONDARY IMPACT TO THE HEAD
ONLY PRESENT RESULTS HERE
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WRAP PROJECTION: MODEL RESULTS
WOOD, SIMMS AND WALSH, IMECHE 2004
MEAN AND VARIABILITY
CONFIDENCE LIMIT CRITERIA: TABLES FOR RECONSTRUCTION
The 50%ile or probable range
– of value in injury and in civil law
The 95%ile range - application in general civil law and in depth research
The 99.8%ile range- the ‘Overall’ confidence limits, corresponds to ‘beyond reasonable doubt’ required for criminal law cases.
SIMMS, WOOD AND WALSH, IJCRASH 2004
PEDESTRIAN IMPACT: THE EFFECT OF PEDESTRIAN MOTION ON HEAD CONTACT
FORCES WITH VEHICLE AND GROUND
SIMMS AND WOOD: PRESENTED SEPTEMBER 2005 AT INTERNATIONAL RESEARCH COUNCIL ON BIOMECHANICS OF IMPACT CONFERENCE PRAGUE
SIMMS AND WOOD, IJCRASH 2006
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BACKGROUND
1980’S: REAL WORLD PEDESTRIAN ACCIDENTS:– HIGH IMPACT SPEEDS, HEAD INJURIES FROM VEHICLE RATHER THAN ROAD
IMPACT. – AT LOW SPEED THE GROUND IMPACT INCREASES IN IMPORTANCE
(LESTRELIN ET AL, 1985).
– BELOW 7 M/S IMPACT SPEED, INJURY FROM THE GROUND IMPACT WAS HIGHER THAN FROM VEHICLE IMPACT, BUT THIS REVERSED AT HIGHER SPEEDS
(ASHTON, 1982; ASTON AND MACKAY, 1983).
– SINCE THEN, CONSIDERABLE DEVELOPMENT OF CAR FRONTS.
– HAS THE ROLE OF THE GROUND CONTACT CHANGED IN IMPORTANCE?
METHODS: MADYMO MULTIBODY PEDESTRIAN MODEL & SIMPLIFIED VEHICLE GEOMETRY
COLEY ET AL, 2001SIMPLIFIED CONTACT FUNCTIONS
MODEL CONFIGURATIONS
1 2 3
4 5
1. FACING SIDE2. 45 DEGREES3. FACING VEHICLE4. SIDE: LEFT LEG BACK5. SIDE: RIGHT LEG BACK
VEHICLE IMPACT SPEED: 5, 10 & 20m/s
FACING SIDEWAYS: HIGHER EFFECTIVE RADIUS OF ROTATION ABOUT THE BONNET LEADING EDGE YIELDS SLOWER ROTATION THAN FRONT BACK CASE
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HEAD VEHICLE IMPACT FORCE
FACING VEHICLE YIELDS MORE SEVERE HEAD IMPACT DUE TO BODY GEMOETRY
ALMOST RANDOM VARIATIONS IN TIMING AND MAGNITUDE
HEAD GROUND IMPACT FORCE
VEHICLE & GROUND CONTACT COMPARISON:
FORCE AND VELOCITY CHANGE (dV)
CONCLUSIONS
INITIAL PEDESTRIAN STANCE AND SPEED HAVE A SIGNIFICANT EFFECT ON THE VEHICLE/HEAD CONTACT FORCE.
FOR PEDESTRIAN/GROUND CONTACT, VERY LARGE & RANDOM VARIATIONS IN CONTACT FORCE OCCUR AS A RESULT OF DIFFERENT BODY PARTS ABSORBING THE GROUND IMPACT.
HEAD CONTACT WITH THE GROUND RESULTS IN HIGHER FORCES ACTING OVER A SHORTER DURATION THAN THE VEHICLE HEAD CONTACT FORCE.
CONTAINMENT OF THE PEDESTRIAN ON THE VEHICLE TO PREVENT GROUND IMPACTS CAN YIELD OPTIMUM RESULTS AT LOW SPEEDS. ENCOURAGING, AS LOW SPEED CONTAINMENT IS A MORE REALISTIC PROSPECT THAN AT HIGH SPEED
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THE INCREASED INJURY RISK TO PEDESTRIANS FROM SUVS
COMPARED TO CARS
SIMMS AND WOOD PRESENTED AT WORLD CONGRESS OF BIOMECHANICS, MUNICH 2006
Context of research
•In Europe, SUVs represent 15% of new vehicle registrations[PriceWaterhouseCoopers, 2004]
•SUVs have different mass and shape than passenger cars.
•What is the effect of differences between cars and SUVs on injury patterns of struck pedestrians?
IMPROVED DESIGN OF VEHICLE FRONTS
Review of empirical evidence of SUV risks
Ballesteros et al: real accident data 1995-1999 [AAP, 2004]
<50km/h odds ratio for pedestrian risk from SUVs compared to cars 2.0 for traumatic brain injury2.0 for thoracic injury 2.5 for abdominal injuries.
However, only 4.5% of cases actually involved an SUV, compared to 66% of cases involving cars.
Review of empirical evidence of SUV risks
Lefler & Gabler [AAP, 2004] real world data from the US
– 11.5% of pedestrians struck by large SUVs killed– 4.5% for pedestrians struck by cars killed
Roudsari et al [IP, 2004]– Light truck type vehicles (LTVs): threefold higher risk of severe
injuries to pedestrians than cars.
Effect most pronounced at lower speeds
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Roudsari et al [TIP, 2005] PCDS: 3146 injuries in 386 pedestrians
- No difference in impact speed between LTVs and cars.
- 159 adults with head injuries, of which 46 struck by LTVs
0.003
0.001
0.16
p value
33%
37%
54%
LTVs
1.818%Abdomen injuries
1.920%Thorax injuries
1.246%Head injuries
Response ratio: LTVs/cars
Cars
Vehicle factors for pedestrian risk:Mass, Geometry & Stiffness
[Lefler & Gabler, AAP 2004]: Pedestrians mass << vehicle masssuggest frontal geometry is controlling factor … but no elaboration
Ballesteros et al [AAP, 2004]: Higher bumper & bonnet heights in SUVs dictate initial contact points.. but no comment on momentumtransfer
Roudsari et al [TIP, 2005]: trajectory governed by pedestrian cg and bonnet leading edge height… but no comment on effect of direct impact against the pelvic/abdomen region.
Stiffness important – but no data
Empirical studies show substantially increased risk for pedestrians when struck by high fronted vehicles compared to a passenger car.
However, conflicting evidence on relative risk of head injuries from these different vehicle types, and no agreement on the source of the increased risk of LTVs for pedestrians.
Summary of empirical evidence of SUV risks
Current work aims to answer these questions
Methods: Madymo pedestrian and vehicle models to simulate dummy impacts of [OKAMOTO ET AL, 2001]
VALIDATION: POLAR DUMMY IMPACT AT 40KM/H WITH CAR & SUV– UPPER LEG REACTION TORQUES – HIGH SPEED VIDEO
MIZUNO & KAJZER, 2000; LIU ET AL 2002
carSUV
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Validation: car impact[OKAMOTO ET AL, 2001]
0ms 20ms 40ms 60ms 80ms
Validation: Suv Impact[OKAMOTO ET AL, 2001]
0ms 20ms 40ms 60ms 80ms
Validation: Upper leg joint reaction torques [OKAMOTO ET AL, 2001]
Simulation matrix
(d)(c)(b)(a)(a)pedestrian facing car (b)pedestrian facing SUV(c) pedestrian sideways to car (walking stance, struck leg back) (d)pedestrian sideways to SUV (walking stance, struck leg back
5, 10 and 15m/s impacts, braking
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10m/s snapshots
Results: side struck pedestrian head resultant acceleration
Results: Pelvis resultant acceleration Head injury predictions: HIC
Head Injury Predictions using HIC criterion: Injury reference level = 1000
( )2
1
2.5t
safe 2 12 1 t
1HIC max a( t ).dt t t 1000t t
= − < −
∫
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Pelvis injury predictions: acceleration
Pelvis Injury Predictions using peak acceleration criterion (m/s2): Injury reference level = 716m/s2
Effects of vehicle mass
( ) impactvehiclepedestrianvehicle
vehiclecgpedestrian v
MhMMkkMv
++= 22
2
_
k = pedestrian radius gyration
h = vertical offset between bonnet leading edge height and pedestrian cg
Primary impact with vehicle: Wood IMechE, 1988
Effects of vehicle masshead pelvis Conclusions on the effect
of vehicle front shape on pedestrian injuries
Head injuries similar or slightly lower from contact with SUVs compared to cars
Injuries to mid body regions are substantially higher.
Primary reason for increased hazard to pedestrians from SUVs is the high front shape of the bumper and bonnet.
Location of primary impact means mid body region is directly struck in a SUV/pedestrian collision, allowing less rotation of the body.
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Conclusions on the effect of vehicle front shape on pedestrian injuries
For pedestrians struck by SUVs there is the combination of a harder primary impact which occurs directly with the critical mid body region.
The mass difference between cars and SUVs not significant for pedestrians
Lowering the bumper and bonnet and reducing bonnet stiffness forSUVs would help to reduce injuries to these mid body regions.
[Simms and O’Neill, British Medical Journal, 2005]
[Simms & Wood, IMechE 2006]
SIZE DOES MATTER
Thank you