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1
Q

What does the “A” value in Crush represent?

A

The coefficient representing the beginning of plastic deformation.
A = (w)(b0)(b1)/gL
Units = Lbs/In

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2
Q

What does the “B” value in Crush represent?

A

The coefficient representing the stiffness of the vehicle structure.
B = (w)(b1)^2/gL
Units = Lbs/In

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3
Q

What does the “G” value in Crush represent?

A

The integration constant which represents the elastic work done to reach a force of “A.” Energy dissipated before permanent damage, aka Restitution
G= A^2/2B
Units = Pounds

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4
Q

What methodologies calculate delta-V?

A

Crush and Momentum

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5
Q

When must the momentum along both the “x” and “y” axis be considered?

A

When two vehicles whose angles of engagement exceed 10 degrees

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6
Q

In angled collisions (when using momentum calculations), what are V-1 and V-2 entry and exit signs?

A

—Based on Heading Angle—
V-1 Entry = 0 degrees
V-2 Entry = Psi (pitch fork looking symbol)
V-1 Exit = Theta (O with line looking symbol)
V-2 Exit = Alpha (A”ish” looking symbol)

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7
Q

When does separation occur?

A

Occurs when the collision force of the impulse between the vehicles has stopped.

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8
Q

What is the Big Mother Rule?

A

Delta-V1/Delta V2 = W-2/W-1

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9
Q

Name the different collision types?

A

Collinear
Central
Central Collinear

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10
Q

What are the five basic pedestrian trajectories in frontal collisions?

A

Wrap, Forward Projection, Fender Vault, Roof Vault, Somersault

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11
Q

Describe the Forward Projection (Pedestrian Trajectory).

A
  • Usually occurs with a smaller Ped and a normal sized vehicle or an adult Ped and a full size pickup or van.
  • PDOF above COM of Ped (Ped COM below the hood line)
  • Speed match-up likely
  • The second most common Ped trajectory
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12
Q

Describe a Wrap pedestrian trajectory.

A
  • The Ped’s head and torso bend around the hood
  • Ped’s COM is above the hood line
  • Ped’s body contacts hood, windshield, A-pillar
  • Usually a decelerating vehicle
  • Close to speed match-up
  • Most common Ped trajectory
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13
Q

Describe a Fender Vault pedestrian trajectory.

A
  • Typically involves adults with normal sized vehicles
  • With Braking Vehicles: Ped usually struck near corner of vehicle, wraps over fender, falls
  • With Non-Braking Vehicles: Ped usually struck near corner of vehicle, slides up hood or fender to A-pillar. Vehicle then decels and causes Ped to fall. Rear wheels can hit head or legs
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14
Q

Describe a Roof Vault pedestrian trajectory.

A
  • Usually high speeds
  • Typically Ped’s COM is higher than hood edge line
  • Ped is lofted in the air, over the hood/roof
  • Ped lands behind the vehicle but may strike roof or trunk
  • Usually no braking
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15
Q

Describe a Somersault pedestrian trajectory

A
  • Usually high speeds or contact with lower portion of the Ped’s body
  • Normally a decelerating vehicle
  • Least common Ped trajectory
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16
Q

What are the three phases of impact for a Pedestrian collision?

A
  1. Impact - The Ped is accelerated
  2. Flight - W/Decel: Ped and vehicle may separate
    W/No Decel: Ped may remain on vehicle
  3. Sliding/Rolling/Tumbling: After impact and hitting ground, body tumbles, rolls, and slides to a stop
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17
Q

What does CRASH 3 stand for?

A 
Calspan
Reconstruction
of
Accident
Speeds
on 
Hihgways
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18
Q

When is Crush not validated (Hint: There are 9)?

A
  1. Roll Over
  2. Yielding fixed objects that break away
  3. Impacts other than a horizontal impacts (+,- 15 degrees)
  4. Severe over/under ride
  5. Undercarriage damage
  6. Large moving vehicles - Greater than 10,000 lbs
  7. Easily moveable objects
  8. Non-central collisions (i.e. sideswipe)
  9. Multiple impacts to the same body area
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19
Q

What are the problems with Small vs. Large vehicles in momentum calculations?

A
  • Determination of entry and exit angles
  • Small errors in post-collision velocities can have substantial impact on the calculated pre-collision velocity of the smaller vehicles.
  • A very small variance in entry/exit angle of the large vehicle can have substantial effect on the calculated pre-collision velocity of the smaller vehicle
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20
Q

What has an affect of the rollover threshold ?

A
  • Load distribution and mass
  • Suspension loading/unloading
  • Tires
  • Multiple Axles
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21
Q

What can be expected with motorcycles both wheel braking?

A
  • A straight rear wheel tire friction mark is normally associated with both front and rear wheel braking
  • The application of the front brake provides more stability during braking and yields maximum braking efficiency
  • The front tire does not generally leave a TFM
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22
Q

What can be expected with motorcycles both wheel braking?

A
  • A straight rear wheel tire friction mark is normally associated with both front and rear wheel braking
  • The application of the front brake provides more stability during braking and yields maximum braking efficiency
  • The front tire does not generally leave a TFM
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23
Q

What can be expected with motorcycles rear wheel only braking?

A
  • Will normally leave a wavy TFM
  • The locked rear wheel tire has used up all the available friction longitudinally, therefore, the tire has 100% slip laterally and will easily be influenced by the roadway contour/slope, weight shifts, steering input, etc.
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24
Q

What can be expected with motorcycles front wheel only braking?

A
  • TFM will be dark, straight, and short

- Steering geometry will cause the motorcycle to quickly go down.

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25
Q

Big Rig Dynamics when locking the truck’s front tires (steering axle)?

A
  • Loss of steering
  • Vehicle will remain directionally stable
  • Jack-knife possible
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26
Q

Big Rig Dynamics when locking the truck’s rear tires (drive axle)?

A
  • Jack-knife will occur rapidly

- Generally irreversible

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27
Q

Big Rig Dynamics when locking the trailers tires?

A
  • Trailer slowly swings out

- Generally is reversible if brakes are released

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28
Q

What are the causes of a jack-knife?

A
  • Locking driver wheel of tractor but not trailer wheels
  • Sharp steering input puts the tractor but not the trailer into a yaw
  • During evasive maneuvers, trailer pushes out the tractor from behind
  • Brake lag time and poor timing on brake application from individual wheels
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29
Q

Explain Entry and Exit angles

A 
Entry = From just prior to first contact to first contact
Exit = From maximum engagement to separation
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30
Q

What is the Kinetic Energy equation?

A

KE = 1/2mv^2

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31
Q

What is translation?

A

Linear motion without rotation

- Must act through the COM

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32
Q

Where is the COM in a passenger vehicle normally located?

A
  • Diagonally from LR wheel to RF wheel and LF wheel to RR wheel (where they cross X)
  • 1/3 the height of the vehicle
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33
Q

P=mv

A

Momentum = Mass x Velocity

34
Q

Explain Inelastic

A
  • Some kinetic energy is lost (deformation)

- Ex: a “head on” collision between two pieces of soft clay…traffic collision are inelastic

35
Q

Explain Elastic

A
  • No kinetic energy is lost

- Ex: Two billiard balls in a head on collision

36
Q

What force does not act on a body?

A

Cetrifugal Force

“The fake force”

37
Q

Explain the difference of Mass and Weight

A

Mass = Amount of matter in a body

Weight = Gravities effect on that mass (weight = mass x gravity)

38
Q

What is the best method for measuring distance of a straight locked wheel TFM (when calculating velocity)?

A
  • The longest skid mark
39
Q

What is the drag factor formula?

A

Drag Factor = acceleration / gravity (f=a/g)
Ex: Negative acceleration rate of 23fps (vehicle slowing), what is f?
-23/-32.2 = .714

40
Q

What has significant effect on friction values?

A
  • Slope
  • Tire Compound (Commercial vs Passenger tires)
  • Vehicle braking efficiency (BE)
  • Loose material on the surface
41
Q

What does NOT have an effect on friction values?

A
  • Tire grade
  • Tread depth
  • Tire pressure
  • Surface temperature
  • Pavement texture
  • Aerodynamic drag
42
Q

Centripetal vs Centrifugal

A

Centripetal = “Central Seeking.” Component of force acting on a body in curvilinear motion that is directed towards the center

Centrifugal = The “apparent” force, equal and opposite, to centripetal force

43
Q

When is the use of a drag sled not appropriate?

A
  • Not appropriate on soft surfaces such as grass, sand, or gravel
44
Q

“f” adjustments for speed

A
  • A negative .1 adjustment for speeds over 30 mph
  • At lower speeds, the vehicle spends a higher percentage of total stopping time in static friction. The coefficient of friction decreases with increased speed
45
Q

“f” adjustment for slope

A

Slope = Rise / Run

  • Add for uphill slope
  • Subtract for downhill slope
  • Due to gravity/normal forces
46
Q

“f” adjustment for tires

A
  • A negative .2 adjustment for commercial tires
  • Commercial tires comprised of a rubber that is harder and stiffer than passenger vehicle tires.
  • Commercial tires last longer but sacrifice some of the tires ability to adhere to the roadway
  • Exposed to higher temps
  • Higher psi
47
Q

Time-G Graph

A

G on the Y axis
Time (seconds) on the X axis
Has first and second peaks with a trough in between

48
Q

Piecewise vs CHP Method

A

Piecewise - Rotation with translation that is not straight

CHP Method - Straight, 0 degrees to 20 degrees equals free rolling, 20+ degrees equals locked wheel

49
Q

When not using wheel by wheel method to calculate velocity, what do you use?

A

COM path of travel

50
Q

What is the formula for velocity?

A

Delta-D / Delta-t

Change in distance over change in time

51
Q

What is the formula for acceleration?

A

Delta-V / Delta-t

Change in velocity over change in time

52
Q

Formula for weight

A

Weight = Mass x Gravity

53
Q

What unit is velocity measured in?

A

fps

54
Q

What unit is acceleration measured in?

A

fps^2

55
Q

What unit is force measured in?

A

Pounds

56
Q

What unit is weight measured in?

A

Pounds

57
Q

What unit is mass measured in?

A

Slugs

58
Q

What unit is work measured in?

A

Foot-Pounds

59
Q

What unit is kinetic energy (KE) or potential energy (PE) measured in?

A

Foot-Pounds

60
Q

What are Newton’s Laws?

A

First - Inertia (Object in motion will stay in motion / object at rest will stay at rest unless acted on by an outside force).
Second - F=ma
Third - Equal and Opposite (For every action, there is an equal and opposite reaction).

61
Q

What is the basic speed concept?

A
  • An energy equivalent to the work done over the distance under study that is solved for velocity
62
Q

What are the four tire friction marks?

A 
S.L.I.P
S - Side Skid
L - Lock wheel
I - Impending
C - Critical Speed Scuffmark (CSS)
63
Q

Newton’s First Law

A

Inertia (i for inertia and i as in 1st)

  • Body in motion / body at rest will stay in motion / at rest unless acted on by an outside force
  • Example: A car moving in a certain direction, will take an equal or greater force to stop its motion, such as a car moving in the opposite direction with the same force.
64
Q

Newton’s Second Law

A

Acceleration
F=ma
1/2m(2A) = 1m(1A) = 2M(1/2A)

65
Q

Newton’s Third Law

A

Equal and Opposite
- For every action there is an equal and opposite reaction
Example: When you step off a boat onto a dock, the boat moves. The force that the person uses to push himself forward, ends up pushing the boat backwards in equal, yet opposite manner.

66
Q

What are the Critical Speed Scuffmark indicators (Hint: there are 8)?

A
  • Less than 20 degrees or 1/3 of wheelbase
  • Start thin and widen
  • Arced
  • Decreasing radius
  • Angled Striations
  • Rotating Tires
  • Outboard rear tire tracks outside of outboard front tire
  • Outboard front tire leaves the darkest mark
67
Q

What is the rule for adding speeds to Critical Speed Scuffmarks?

A
  • Do NOT combine speeds determined from TFMs after the CSS - Can only compare
  • Speeds determined from TFMs prior to the CSS can be added using Kinematic equations or combined speed equation
68
Q

PDOF

A

Principle Direction of Force

  • An indication of the magnitude and direction of the opposing forces acting on a vehicle
  • It is the Vecctor sum of the forces acting during a collision
  • The direction or line of action along which impulse occurs
69
Q

Maximum Engagement

A
  • Occurs when the greatest force or maximum penetration to the vehicles occurs
70
Q

Collinear Collision

A
  • Occurs when the entry angle between the involved vehicles is 10 degrees or less (either head on or rear end) based on COM
71
Q

Central Collinear Collision

A
  • When the COM of one vehicle acts through the COM of the other vehicle
    - - Speed match-up occurs and vehicles separate (exit) at the same velocity
72
Q

Impulse

A
  • Occurs along the PDOF
  • Impulse equals the change in momentum (Delta-P)
  • Transfer of momentum between two bodies is described as impulse
  • F(Delta-t) = M(Delta-V)
  • F(Delta-t) represents Impulse
  • M(Delta-V) represents Change in Momentum
73
Q

What will cause a TFM?

A

Extreme Acceleration
Extreme Deceleration
Extreme Change of Direction

74
Q

What is a tire abrasion with smear?

A
  • A smear of tar/asphalt along with abrasions of tire material. They’re long lived and most common on Asphalt-Concrete (A/C) surface
75
Q

What is the primary marking mechanism on Portland Cement Concrete (PCC)?

A

Tire Abrasions

  • The texture of the roadway abrades material from the tire. Particles ground off the tire appear as rubber particles along the path of the tire.
  • The roadway is acting as sandpaper
76
Q

What is the best method for determining the distance the vehicle traveled if it is rotating during deceleration?

A

The COM path of travel

77
Q

When does a Critical Speed Scuffmark transition to a Side Skid?

A
  • When the heading direction of the vehicle exceeds 20 degrees from the COM path of travel of the vehicle (or 1/3 the wheelbase).
78
Q

Velocity-Time graph

A

Represents Acceleration

  • Velocity on the Y axis
  • Time on the X axis
  • Equals Velocity / Time = Acceleration
79
Q

Position-Time graph

A

Represent Velocity

  • Position on the Y axis
  • Time on the X axis
  • Equals Position / Time = Velocity
80
Q

Force is measure in?

A

Pounds

81
Q

Mass is measure in?

A

Slugs

82
Q

Velocity is measured in?

A

FPS

TARSC (6 decks)

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