IPTM Special Problems 2013

Cavalier v Park Avenue Crash Analysis – EDR’s

Copyright Ruth Consulting LLC 2012, Authorized for use by IPTM 1

Point of this Research• Research tells us that Delta V in EDR’s is a

valuable tool in reconstructing central collisions.• In non-central collisions, Delta V measured in the

EDR will typically under-report the crash. Using the Delta V to calculate closing speeds or impact speeds results in conservative estimates of speed.

• Objective: Describe and Quantify what is causing the under-reporting, then develop a simplified adjustment to correct the measurement, using the Effective Mass Ratio.

1998 Cavalier

1995 Buick Park Avenue

CRASH 1 FRIDAY MAY 17 EDR’sStock X EDR under RF seat

Stock X EDR under RF seat

Ride Along EDR

Ride Along EDR

FAIL

FAIL

1998 Cavalier 2766 lbs

1995 Buick Park Avenue 3368 lbs

CRASH 1 FRIDAY MAY 17 RESULTSSTOCK EDR’s – NO RECORDINGS

RIDE ALONG -4.46X, +12.1Y = PDOF 70o

RIDE ALONG -18.46X, -5.73Y =PDOF 17o

PDO

F

Ride Along EDR

Ride Along EDR

TRADITIONAL EDR ANALYSIS (No EMR)• Use Closing Speed -assuming right angle collision,

target has no velocity in Cavalier direction of travel, so Closing Speed in the Cavalier X = V1

V1 = (|Cavalier X ΔV| + |Buick Y ΔV|)*(1/(1+e))V1 = (|-18.46| + |12.1|) (1/(1+.1))V1 = 30.56 mph*.91 = 27.8 mph• Using Post Impact Speed and Delta VV1 = V3cosβ-ΔVx = 15.3cos(10) - - 18.46V1 = 15.3(0.98) + 18.46 = 15.1+18.46 = 33.56 mphFor this instrumented crash, we know the bullet was going 41 mph – so WHY did it under report?

1998 Cavalier 2766 lbs

1995 Buick Park Avenue 3368 lbs

ANSWER: IT’S AN OFFSET COLLISIONMEASURE OFFSET OF PDOF FROM CG

THEN ADJUST FOR EFFECTIVE MASS RATIO

PDO

F

BUICK 48” OFFSET

CAV 22.9” OFFSET

Effective Mass Ratio Calculation

CAVALIERLookup: CAV Yaw Moment of Inertial = 1490 Cav Weight = 2766Calculate k2

k2 = Iyg/W = 1490 (32.2ft/sec2)/2766 lbs k2 = 17.35

Calculate Effective Mass Ratio Gamma (ϒ)ϒ = k2/(k2 + h2) = 17.352/(17.352 + 1.92) ϒ = 0.83

Effective Mass Ratio Calculation

BUICKLookup: Yaw Moment of Inertial = 2433 Weight = 3368Calculate k2

k2 = Iyg/W = 1490 (32.2ft/sec2)/3368 lbs k2 = 23.26

Calculate Effective Mass Ratio Gamma (ϒ)ϒ = k2/(k2 + h2) = 23.262/(23.262 + 4.02) ϒ = 0.58

Applying the Adjustment

• Divide the measured ΔV by ϒ (Gamma)• Cavalier • (-18.46X, -5.73Y)/.83 = -22.2X, -6.9Y• Buick• (-4.46X, +12.1Y)/.58 = -7.6X, 20.7Y

Cavalier EDR Offset 1.9ft

EMR 0.58Adjusted DV 22.0 (7.6X, 20.7Y)

EMR Adjusted Delta V’s

Buick Offset 4.0 ftYaw Moment of Inertia 2433

Yaw Moment of Inertia 1490EMR 0.83

Adjusted DV 23.2 (22.2X, 6.5Y)

Note adjusted total DV’s are very close to equal.

EMR ADJUSTED EDR ANALYSIS• Use Closing Speed -assuming right angle

collision, target has no velocity in Cavalier direction of travel, so Closing Speed in the Cavalier X = V1

V1 = (|Cavalier X ΔV| + |Buick Y ΔV|)*(1/(1+e))V1 = (|-22.2| + |20.7|)*(1/(1+.1))V1 = 42.9 mph * .91 = 39.0 (Range 35.1-42.9)• Using Post Impact Speed and Delta VV1 = V3cosβ-ΔVx = 15.3cos(10) - - 18.46V1 = 15.3(0.98) + 22.2 = 15.1+22.2 = 37.3 mph

(Range 35.1 to 39.4)

Estimating Effective Mass Ratio

• If you are intimidated by the effective mass ratio calculation, the next slide shows you EMR calculations for several different vehicle sizes versus offset in feet.

• You can see where the Cavalier and Buick calculations would be consistent with the chart.

• Use the chart for first pass estimates.

Effective Mass Ratios for Different Vehicles

Buick

Cavalier

IPTM Special Problems 2013

Impala vs Eldorado Crash Analysis – EDR’s

Copyright Ruth Consulting LLC 2012, Authorized for use by IPTM 14

Point of this Crash• The Cavalier vs Buick crash a significant offset• This crash is a more central crash • The point is to show that the EDR captures this

crash well without any necessary adjustments

2005 Chevy Impala

1995 Cadillac Eldorado

CRASH 2 Tuesday AM – Impala vs Eldorado

Stock X EDR under RF seat

Stock X EDR under RF seat

Ride Along EDR

FIL

FAI

2005 Chevy Impala 3764 lbs

1995 Cadillac Eldorado 3891 lbsStock EDR -5.16X @ 100ms, -6.69@300

CRASH 2 Tuesday Impala vs Eldorado RESULTS

Ride alongEDR -5.73X, +19.73Y = PDOF 74o

Stock EDR -20.67X, -7.75Y =PDOF 21o

LAST REPORTED SPEED 40 MPH

PDO

FRide Along EDR

Stock EDR

Stock EDR

Copyright Ruth Consulting LLC 2012, Authorized for use by IPTM

18

Work the Impala EDR speed data• Use speed at impact worksheet for speed data

MIN MAXLast data 40 40Spd loss bef imp -0 1Wheel slip 0 0Speedo +/-4% -1.6 +1.6RANGE 38.4 42.6

IMPALA EDR DELTA V ANALYSIS (No EMR)

• Use Closing Speed -assuming right angle collision, target has no velocity in Impala direction of travel, so Closing Speed in the Impala X = V1

V1 = (|Impala X ΔV| + |Eldo Y ΔV|)*(1/(1+e))V1 = (|-20.67| + |19.73|) (1/(1+.1))V1 = 40.4 mph*.91 = 36.7 mph (33 to 40.4)• Using Post Impact Speed and Delta VV1 = V3cosβ-ΔVx = 22.1 cos(30) - - 20.7V1 = 22.1(0.87) + 18.46 = 19.2+20.7 = 39.9 mph (Range 37.9- 41.9)GOOD AGREEMENT WITH ACTUAL SPEED 41 MPH

EDR Reconciliation with Scene Evidence

• Momentum Analysis 38.5 • EDR Speed 38.4------------42.6 • EDR Closing Speed 33--------------40.4• EDR + postcrash 37.9----------41.9

IPTM Special Problems 2013

Impala v Saturn Crash Analysis – EDR’s

Copyright Ruth Consulting LLC 2012, Authorized for use by IPTM 21

Point of this Crash• Another offset crash to investigate EMR

further• We are expecting the EDR to under report,

and that it will require an EMR adjustment to more accurately reconstruct the crash

2000 Impala

1994 Saturn (no stock EDR)NOT MOVING

CRASH 3 TUESDAY PM EDR’s

Stock X EDR under RF seat

Ride Along EDR

FAI

2000 Impala 3389 lbs

1994 Saturn 2305 lbs

CRASH 3 TUESDAY PM EDR’sRIDE ALONG -4.46X @100ms (grows to -8.28 @ 300)

-20.37Y @ 100MS (grows to -25.46 @ 300ms)

= PDOF 78o

STOCK EDR -15.32X 50 MPH LAST REPORTED SPEED

PDOF 12 based on Saturn EDR

PDO

FRide Along EDR

Stock EDR

Copyright Ruth Consulting LLC 2012, Authorized for use by IPTM

25

Work the Impala EDR speed data

• Use speed at impact worksheet for speed data MIN MAX

Last data 50 50Spd loss bef imp -0 +4Wheel slip 0 0Speedo +/-4% -2.0 +2.0

48.0 56.0

TRADITIONAL EDR ANALYSIS (No EMR)• Use Closing Speed -assuming right angle collision,

target has no velocity in Cavalier direction of travel, so Closing Speed in the Impala X = V1

V1 = (|Impala X ΔV| + |Saturn Y ΔV|)*(1/(1+e))V1 = (|-15.3| + |20.4|) (1/(1+.05))V1 = 35.7 mph*.96 = 34.3 mph• Using Post Impact Speed and Delta VV1 = V3cosβ-ΔVx = 31.1cos(4) - - 15.3V1 = 31.1(0.99) + 15.32 = 30.8+15.3 = 46.1 mphFor this instrumented crash, we know the bullet was going 50 mph – so WHY did it under report?

2000 Impala 3389 lbs

1994 Saturn 2305 lbs

ANSWER: IT’S AN OFFSET COLLISIONMEASURE OFFSET OF PDOF FROM CG

THEN ADJUST FOR EFFECTIVE MASS RATIO

PDO

F

SATURN OFFSET 3’

IMP OFFSET 1’

Estimating Effective Mass Ratio

• If you are intimidated by the effective mass ratio calculation, the next slide shows you EMR calculations for several different vehicle sizes versus offset in feet.

• Use the chart for first pass estimates.

Effective Mass Ratios for Different Vehicles

Saturn

Impala

Effective Mass Ratio Calculation

IMPALALookup: Yaw Moment of Inertial = 2285 lb-ft-sec2 Weight = 3389Calculate k2

k2 = Iyg/W = 2285 (32.2ft/sec2)/3389 lbs k2 = 21.77

Calculate Effective Mass Ratio Gamma (ϒ)ϒ = k2/(k2 + h2) = 21.71/(21.71 + 1.02) ϒ = 0.96

Effective Mass Ratio CalculationSATURNLookup: Yaw Moment of Inertial = 1168 Weight = 2305Calculate k2

k2 = Iyg/W = 1168 (32.2ft/sec2)/2305 lbs k2 = 16.32

Calculate Effective Mass Ratio Gamma (ϒ)ϒ = k2/(k2 + h2) = 16.322/(16.322 + 3.02) ϒ = 0.64

Applying the Adjustment

• Divide the measured ΔV by ϒ (Gamma)• Impala • (-15.32X/.96) = -16.0X• Saturn• (-4.46X, -20.37Y)/.64 = -6.9X, 31.6Y

Impala EDR Offset 1.0ft

EMR 0.64Adjusted DV (6.9X, 31.6Y)

EMR Adjusted Delta V’s

Saturn Offset 3.0 ftYaw Moment of Inertia 1186

Yaw Moment of Inertia 2285EMR 0.96

Adjusted DV 16.0X

EMR ADJUSTED EDR ANALYSIS• Use Closing Speed -assuming right angle collision,

target has no velocity in Cavalier direction of travel, so Closing Speed in the Cavalier X = V1

V1 = (|Impala X ΔV| + |Saturn Y ΔV|)*(1/(1+e))V1 = (|-16.0| + |31.6|)*(1/(1+..05)V1 = 47.6 mph * .96 = 45.7 (Range 41-50)• Using Post Impact Speed and Delta VV1 = V3cosβ-ΔVx = 31.10cos(4) - - 16.0V1 = 31.1(0.99) + 16.0 = 30.8+16.0 = 47.8 mph

(Range 46.2 to 49.4) BETTER AGREEMENT

EDR Reconciliation with Scene Evidence

Momentum Analysis 52 EDR Speed 48------------56 EDR Closing Speed 41------------50EDR + postcrash 46---49

CONCLUSIONS• Delta V does a good job of predicting impact

speeds in CENTRAL collisions• Delta V UNDERESTIMATES impact speed in

OFFSET collisions• Using the Effective Mass Ratio adjustment

improves the accuracy of impact speed estimates.• We may need to make further adjustments to

EDR location if it more offset than CM from PDOF• We need to pay more attention to estimating

RESTITUTION when calculation closing speeds.

IPTM Special Problems 2013

END

Rick Ruth 313 910 5809ruthconsulting@comcast.net

Copyright Ruth Consulting LLC 2012, Authorized for use by IPTM 37