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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