
  Ŀ
                                                             
      iCAR - Intelligent Computer-Assisted Reconstruction    
                          Version 2.4                        
                                                             
                 (c) James G. Perry 1990,1991,1992,1993      
                                                             
  
   




 

                             Notice
                             ------

This is a development test release of iCAR.  Use these programs
at your own risk.  Although they have been extensively tested,  I
take no responsibility for any losses.


                        Not Public Domain
                       ------------------

This document and the iCAR program are the personal property of:

                         James G. Perry
                        5431 Stirrup Way
                       Oceanside, CA 92056
                          (619)940-1977
						jperry1@ix.netcom.com

iCAR is distributed by me for your personal use.  You may not
charge for distributing iCAR.  Commercial use of iCAR is
prohibited.  Corporations and institutions may not use iCAR
without first obtaining written permission.  Sorry about that,
but if anyone is going to make a buck from this it should be me.
The cost of iCAR is $9.95 plus tax.  People who purchase now
will obtain, at no additional cost, the next revision of iCAR.

Please let me know of any problems, criticisms, or, especially,
suggestions.

Thank you.


                            Trademark
                            ---------

MS-DOS is a registered trademark of Microsoft Corporation
PC-DOS is a registered trademark of IBM Corporation.
LaserJet is a registered trademark of Hewlett-Packard.
Turbo Pascal is a registered trademark of Borland International.
                               
                        Table of Contents


Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  1

Getting Started. . . . . . . . . . . . . . . . . . . . . . . .  2

iCAR and Accident Reconstruction . . . . . . . . . . . . . . .  2

The Menus. . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     Conservation of Linear Momentum . . . . . . . . . . . . .  4
     Speed/Velocity Calculations . . . . . . . . . . . . . . .  5
     iCRASH - Damage Only. . . . . . . . . . . . . . . . . . .  9
     Speed Estimates from Damage . . . . . . . . . . . . . .   10
     Time/Distance Calculations. . . . . . . . . . . . . . .   10
     Utilities . . . . . . . . . . . . . . . . . . . . . . .   12
     DOS Operations. . . . . . . . . . . . . . . . . . . . .   14

Appendix A - Vehicle Parameters. . . . . . . . . . . . . . .   15

Appendix B - Vehicle Size Categories . . . . . . . . . . . .   18

Appendix C - Vehicle Measurement Terms . . . . . . . . . . .   19
                                                          Page 1
Introduction
=================================================================

"You can never be too rich, too thin, or have too much RAM and Disk
storage."  Ancient American proverb, ca. 1980

"The computer is no better than its program."  Elting Elmore
Morison, 1966

"The real problem is not whether machines think but whether men
do."  Burrhus Frederic Skinner, 1969



This manual describes the use and operation of iCAR, an extremely
powerful collection of popular accident reconstruction programs and
calculations assembled into a single,integrated, low-cost package. 
The manual includes installation instructions, a user's guide, and
a reference section.

iCAR was developed with these goals in mind:

- FAST OPERATION - More than anything else, iCAR was designed to 
  operate quickly, especially in these areas;

     - Calculations.
     - Displaying/Updating the screen.
     - Initial loading of files.

- EASE OF USE - This version of iCAR includes:
 
     - Totally menu-driven.
     - Complete execution from a single file (ICAR24.EXE).
     - Automatic recording of results.
     - DOS access.

- COMPACT PROGRAM SIZE - Every effort was made to keep the program 
  size as compact as possible.  Even though memory is getting 
  cheaper all the time, I didn't want iCAR to require any more 
  memory than absolutely necessary.
                                                          Page 2
Getting Started
=================================================================

iCAR is contained on a single 360 kb diskette which contains three
files: iCAR.exe, iCAR.txt and iEdit.exe.  While iCAR can be run
from a floppy drive, it suggested that it be loaded onto a hard
drive.  There are no special loading requirements so you can copy
iCAR from the floppy just like you would with any other file (i.e.,
copy a:\*.* to copy it from the floppy to the hard drive).  To
execute the program, just enter 'icar' at the C:> prompt.


iCAR and Accident Reconstruction
=================================================================

Users of iCAR are assumed to have some accident investigation
experience and training.  In and of itself, accident
reconstruction is as much an art as it is a science.  The
formulas and calculations used in iCAR are not only accepted as
standards in the field, but are also firmly entrenched in solid
scientific principles.   The skills needed to obtain the
necessary information to correctly use iCAR, however, vary
widely.  iCAR assumes it is being give good data and makes no
judgements.  As the saying goes -- Garbage In, Garbage Out.

A good reconstructionist has two traits: the ability to
accurately gather facts and the talent to interpret them.  iCAR
helps in both regards, first, by showing what kind of information
to gather, and second, by reducing the time and effort to distill
the facts into useable information.

Some Hints

1.   Make use of iCAR's ability to record all calculations during
     a single session.
2.   Perform multiple iterations on questionable data using a
     variety of input.
3.   If possible, work with a single vehicle at time.  This
     reduces the inherent bias that occurs when trying to fit
     data items to a specific scenario.
4.   Avoid pre-judging.
5.   Think of iCAR as a tool.  No different than a calculator or
     a compass.  It doesn't answer questions...it helps 'you'
     answer questions.

                                                          Page 3
General Notes

1.   All data items are presented in a table format.  The table
     allows for full-screen editing and complete cursor movement.
2.   There is no need to worry about setting the Caps Lock on or
     off, this is all handled internally.
3.   During data entry, "Note:" fields will usually appear.
     These fields contain important information about the item
     being entered, including: data ranges, types, and general
     information.
4.   All numerical fields use a "real" data type.  I won't bore
     you with significant digits or byte size; the bottom line is
     that you can enter numbers at the level of precision you
     wish.  A number like 3.12325674 is just fine.


                                                          Page 4
The Menus

iCAR is entirely menu-driven.  Simply move the cursor to your
choice and strike the Enter key.  On some systems, depending upon
hardware, a key letter in the menu will be highlighted.  Pressing
this letter will have the same effect as using the cursor/Enter
key combination.

There are six main menu selections.  Each is explained below, as
are any subsequent internal menus.
 
     
                                                       Ŀ
                         iCAR                           
                                                        
                        Main Menu                       
                                                        
              Conservation of Linear Momentum           
              Speed/Velocity Calculations               
              Speed from Damage                         
              Time/Distance/Energy Calculations         
              Utilities                                 
              DOS Operations                            
              Quit                                      
                                                        
      
      


===============================
Conservation of Linear Momentum
===============================
Sounds serious, doesn't it?  Here's the basic formula:

            m1v1 + m2v2 = m1v1' + m2v2'

     Momentum at impact = Momentum following impact

Simply stated, the combined momentum of the vehicles at impact
must be the same after impact.  There is no loss in momentum for
the combined vehicles following impact because linear momentum is
conserved.  One vehicle may gain momentum as a result of the
impact while the other loses some, but together they end up with
the same amount after the impact as before.  Okay, the hard stuff
is out of the way.  How much of this do you need to understand?
Not much, really.  Over 300 years ago, scientists introduced this
concept and it is now accepted as a universal law of nature.
It's right up there with gravity, folks.  From an investigative
point of view, four basic pieces of information are needed: (1)
the weights of the vehicles involved, (2) their post-impact
heading angles, (3) their post-impact speeds, and (4) their pre-
                                                           Page 5

impact heading angles.  The determination of vehicle weight can
come from any number of sources, including: MVMA specificats,    
NATB Manuals, Branhams's Truck Index, etc.  The pre- and post-
impact heading angles are developed from scene evidence and taken
from the diagram.  The post-impact speeds are generally
determined from some mutation of the speed-to-slide-to-stop
formula.

IMPORTANT NOTE:  Quite often, investigators confuse heading
angles with magnetic headings or x/y plotting.  Both of the
latter are important in terms of accurate scene description and
documentation, but only lend confusion when it comes to vehicle
headings.  Vehicle headings, especially in conjunction with
momentum equations, should be vehicle relative.  By this I mean
one vehicle will always have a heading of 0 degrees at approach,
and all other vehicle heading will be taken clockwise and
relative to 0 degrees.  A quick case in point.  Assume there is a
simple intersection-type collision.  Vehicle 1 is heading east
and is broadsided by Vehicle 2 which is heading north.  Taking
Vehicle 1 as the 0-axis vehicle will then make Vehicle 2's
heading angle 270 since it is taken clockwise from the 0-axis.
Similarly, if Vehicle 2 is taken as the 0-axis vehicle, then
Vehicle 1's heading angle will be 90.  So here's the rule: give
one of the vehicles a 0 heading angle and determine all other
angles from this point going clockwise.  Trust me, it makes life
easier.  There are two options under this menu selection.  A
brief discussion of each follows:

     Conservation of Momentum - 90:  Handles basic 90 degree,
     intersection-type collisions.  One vehicle is assumed to
     have a 0 degree heading angle and the other a 90 degree
     heading angle.

     Conservation of Momentum - Oblique:  Handles any other
     collision types with the exception of rear-enders.

===========================
Speed/Velocity Calculations
===========================
Generally speaking, speed and velocity mean the same thing: how
far did something move during a given time.  But the high-brows
got involved and, even though there is a straight mathematical
conversion between the two, many popular formulae require a
differentiation.  Speed is measured in miles and hours (MPH);
velocity is measured in feet per second (FPS).  There is a subtle
difference between the two: speed connotes movement without
regard to direction and velocity describes movement with regard
to direction.  If you need to convert one to the other, just use
the Utilities option of iCAR.                             Page 6

     Speed to Slide to Stop:  This is, without question, one of
     the pillars upon which accident reconstruction is based.  It
     provides a sound, physical relationship which is wholly
     proveable.  Considerations include: accurate assessment of
     the drag factor (including grade, if any), the actual slide-
     to-stop distance, and the percentage of braking.   The
     results of this calculation allows the user to infer only
     one thing-the vehicle must have been going at least that
     fast to stop in the distance measured.

          s = 5.5 dfb 

               where     s = speed in MPH
                         d = distance of slide
                         f = coefficient of friction
                         b = percentage of braking

     Speed to Slide to Stop - 2 surfaces:  This option performs
     the same function as its parent, only 2 surfaces can now be
     computed.  Two surfaces were chosen since the chances of a
     vehicle cross more than that are fairly slim.  The
     calculations for more than two surfaces is identical to the
     calculation for two.

     Critical Curve:  Over the past couple of years, this
     calculation has fallen into some disrepute.  There are some
     questions whether the calculation is over- or
     underestimating the speed.

               s = 3.87 rf

               where     s = speed in MPH.
                         r = radius of curve
                         f = coefficient of friction

     Free Fall:  The main consideration when using this option is
     to ensure that you get your signs right.

          s = 2.74d
              -----
              m (d+h)

          where     s = speed in MPH
                    d = horizonal distance travelled
                    m = takeoff slope
                    h = change in height
                                                          Page 7

     Combined Speeds:  This option takes two speeds and combines
     them to provide a final speed.  Caution should be exercised
     when it comes to combining speeds which are, in and of
     themselves, final speeds.  A good example is a speed derived
     from a fall.  That's the final speed, regardless of what
     happens after the fall.                              Page 8


     Velocity - Known Distance, Known Time:  This is one of the
     basic formulae used in physics.  It determines the
     velocity to travel a known distance during a known time.

               v = d/t

               where     v = velocity in feet-per-second
                         d = distance in feet
                         t = time in seconds

     Velocity Gained/Lost:  When the acceleration/deceleration
     rate is known and the time is known, this calculation will
     yield the velocity gained or lost.

     Velocity At Any Time:  This option will provide the velocity
     at any time during an acceleration/deceleration when the
     initial velocity, acceleration/deceleration rate, and time
     are known.

     Velocity At Any Distance:  This option will provide the
     velocity at any distance during an acceleration/deceleration
     when the acceleration/deceleration rate and distance are
     known.
                                                          Page 9
====================
iCRASH - Damage Only
====================
The iCRASH subprogram computes speed changes experienced during a
vehicle-to-vehicle or a vehicle-to-fixed object collision.  It
makes use of the locations and extent of structural crush and is
based on the same energy calculations used in the CRASH III
program.  Users should be aware of CRASH III techniques and
limitations before selecting this option.  There are two options
under this menu selection.  A brief discussion of each follows:

     New:  Tells iCAR to reset all the numerical fields to 0 and
     clears all buffers.  A fresh entry screen will then be
     presented.

     Rerun:  Retains all data which was entered during the most
     recent New or Rerun compilation and allows the user to make
     changes to any or all data items.

     Showit:  This option first prompts the user to determine if
     a printout is required, then generates a screen image
     showing vehicle damage, PDOF, and D.  At present, the screen
     print utility is limited to use by Hewlett-Packard LaserJet
     products.  A driver for dot-matrix printers is in the works.


Additional Notes:  Whenever New is selected, the user will be
given the option to create an ASCII file which will record the
results from any number of runs.  Also, during each run, the user
is given the option to alter the vehicle stiffness constants.
The decision to offer this option was based on the fact that the
default constants, based primarily on the CRASH III model, have
some age on them now.  More up-to-date information is becoming
available.  If the user has this information, it should be used.
When a larger body of this information becomes available to me, I
will alter the internal constants to reflect this change.
                                                         Page 10

=================================
Speed Estimates from Damage
=================================
Sometimes it is useful to compute a "rule of thumb" estimate of a
vehicle's speed based on damage.  There is one main menu and one
follow-on menu as shown below.

                 Ŀ
                  Speed Estimates from Damage  
                                               
                   1  Frontal Impacts - Menu   
                   2  Rigid Pole Impacts       
                   3  Rear Impacts             
                   4  Quit                     
                 

           Ŀ
                      Frontal Impacts                
                                                     
             1  Full Size - U.S.                     
             2  Compacts & Intermediates - U.S.      
             3  Front Engine, Rear Drive - Foreign   
             4  Front Wheel Drive - Foreign          
             5  Rear Engine - Foreign                
             6  Quit                                 
           

=================================
Calculate Stiffness Values
=================================
Calculate stiffness values based on crash test data.  The
generated values would be used in the CRASH program.

=================================
Time/Distance Calculations
=================================
The following selections are used to determine where a particular
vehicle was relative to another before a collision and to answer
questions as to whether maneuvers by either party could have had
a positive effect.

     Time and Distance to Decelerate

     Time - Known Distance, Known Velocity

          t = d/v

          where     t = time in seconds
                    d = distance in feet
                    v = velocity in feet-per-second
          
                                                         Page 11

     Time - Decelerate From Known Velocity

          t = (vo - vf) / a

          where     t  = time in seconds
                    vo = initial velocity in feet-per-second
                    vf = final velocity in feet-per-second (0 if
                         vehicle came to a stop)
                    a  = acceleration/deceleration rate (the rate
                         is computed by multiplying gravity by 
                         the acceleration/deceleration factor)


     Time - Accelerate From Known Velocity

          t = (vf - vo) / a

          where     t  = time in seconds
                    vo = initial velocity in feet-per-second
                    vf = final velocity in feet-per-second (0 if
                         vehicle came to a stop)
                    a  = acceleration/deceleration rate (the rate
                         is computed by multiplying gravity by 
                         the acceleration/deceleration factor)


     Distance - Known Velocity, Known Time
     

     Constant Speed

          t = d / v

          where     t = time in seconds
                    d = distance in feet
                    v = velocity in feet-per-second

          This option shows the data in a graphical format.

          
     Accelerate from a Stop

          d = .5at

          where     a = acceleration rate
                    d = distance in feet
                    t = time in seconds

          This option shows the data in a graphical format.
                                                         Page 12
==========
Utilities
==========

     Radius of Curvature:  Uses the standard radius of curvature
     formula.  The formula assumes that the curve being measured
     is a regular (constant) curve.  A quick way to check this is
     to make two measurements in addition to the middle ordinate
     measurement.  The two measurements must occur at like points
     (i.e., identical distances along the chord).  If the
     measurements are the same, it's a regular curve; otherwise,
     it is an irregular curve and this calculation is invalid.

          R = (c / 8m) + (m / 2)

          where     R = radius
                    c = chord
                    m = middle ordinate

     Convert FPS to MPH:  Feet-per-second to miles-per-hour.

          mph = fps x 0.6818


     Convert MPH to FPS:  Miles-per-hour to feet-per-second.

          fps = mph x 1.467

     Conversion Formulae:  This option serves as a reference
     source.  There are many conversions.  Most of these are
     simple and not worth valuable computing time when a simple
     calculator will do the job.  This option just provides a
     listing of input to get a desired output.  No more, no less.

     Compute Drag Factor:  For a vehicle with all wheels locked,
     the drag factor is the same as the coefficient of friction.

     The following three selections all determine acceleration
     and/or deceleration factors.  They vary only what it known
     prior to the calculation.

     Compute AD Factor: Speed and Distance Known

          adf = s / 30d

          where     adf = acceleration/deceleration factor
                    s   = speed in MPH
                    d   = distance in feet

                                                         Page 13

     Compute AD Factor: Velocity and Time Known

          adf = v / 32.2t

          where     adf = acceleration/deceleration factor
                    v   = velocity in feet-per-second
                    t   = time in seconds



     Compute AD Factor: Distance and Time Known

          adf = d / 16.1t

          where     adf = acceleration/deceleration factor
                    d   = distance in feet
                    t   = time in seconds


     Compute Acceleration Factor: Vi, Vf, and Time Known:
     Computes an acceleration factor when the initial velocity,
     final velocity, and time are known.

          a = (vf - vo) / (32.2t)

          where     a  = acceleration factor
                    vf = initial velocity in feet-per-second
                    vo = final velocity in feet-per-second
                    t  = time in seconds


     Compute Deceleration Factor: Vi, Vf, and Time Known:
     Computes a deceleration factor when the initial velocity,
     final velocity, and time are known.

          a = (vo - vf) / (32.2t)

          where     a  = deceleration factor
                    vf = initial velocity in feet-per-second
                    vo = final velocity in feet-per-second
                    t  = time in seconds

     Compute AD Rate: AD Factor Known:  Once the factor is known,
     the rate is computed by multiplying the factor time the
     gravity (32.2 feet per second per second).
                                                         Page 14
==============
DOS Operations
==============
iCAR provides the user with two important DOS-related operations.
Both are important and necessary.  Being able to escape into the
DOS shell without leaving a program provides significant
flexibility and a result recording operation which runs in the
background allows the user to concentrate on the difficult task
at hand without having to worry about the details of file
manipulation.

     Exit to DOS:  Temporarily suspends iCAR, clears the screen,
     and displays the DOS prompt, from which you can run other
     programs or DOS commands.  You must remember, however, that
     iCAR is still resident, so your computer will not have as
     much memory as it would normally.  To return from the shell,
     simply type EXIT at the DOS prompt.

     Create an ASCII Session Record:  Creates an ASCII text file
     using a name of your choosing, activates an internal boolean
     variable, and will faithfully record calculations results
     for the duration of the session.  Please remember that the
     file name chosen must follow normal DOS protocol, and that
     any identical file name will be overwritten.  Choose a file
     name that means something to you (i.e., case0914.jp).


                                                         Page 15

Appendix A - Vehicle Parameters

The appropriateness of the set of eight frontal stiffness
coefficients used by the CRASH3 program were examined in an SAE
paper entitled "A Comparison Between NHTSA Crash Test Data and
CRASH3 Frontal Stiffness Coefficients".  The authors (Messrs.
Strother, Woolley, and James) generated a new set of stiffness
categories which are shown on the following page.  
                                                         Page 16

Ŀ
 Stiffness    CRASH3 User's Guide  Strother, et al       
 Categories  Ĵ
                                                       
              A(lbf/in) B(lbf/in) A(lbf/in) B(lbf/in)

Ŀ
 1                                                     
                                                       
 Subcompact    302.0      47.0      237.9       58.9   
                                                       

Ŀ
 2                                                     
                                                       
 Compact       259.0      43.0      240.0       60.0   
                                                       

Ŀ
 3                                                     
                                                       
 Intermediate  317.0      56.0      247.5       58.95  
                                                       

Ŀ
 4                                                     
                                                       
 Full-size     356.0      34.0      236.7       51.5   
                                                       

Ŀ
 5/6                                                   
                                                       
 Largest       325.0      37.0      247.2       57.9   
                                                       

Ŀ
 7                                                     
                                                       
 Vans          383.0      126.0     349.7       99.8   
 MPVs          383.0      126.0     350.9      100.5   

                                                         Page 17

Ŀ
 Stiffness    CRASH3 User's Guide  Strother, et al       
 Categories  Ĵ
                                                       
              A(lbf/in) B(lbf/in) A(lbf/in) B(lbf/in)

Ŀ
 8                                                     
                                                       
 Pickups       480.0       50.0     425.6       72.5   
                                                       

Ŀ
 9                                                     
                                                       
 Front Wheel   373.0       38.0     240.4       58.2   
 Drive                                                 
Page 18

Appendix B - Vehicle Size Categories

          SIZE           WHEELBASE
          ----           -------------

          1               80.9 -  94.8
          2               94.8 - 101.6
          3              101.6 - 110.4
          4              110.4 - 117.5
          5              117.5 - 123.2
          6              123.2 - 150.0
          7              109.0 - 130.0 VANS
          8              PICKUPS [Select 1 to 6 based on wheelbase]
          9              JEEPS [Select 1 to 6 based on wheelbase]
          11             IMMOVABLE BARRIER
                                                         Page 19

Appendix C - Vehicle Measurement Terms


C                   Depth of crush at several positions (usually
                    2, 4, or 6).

CDC                 Collision Deformation Classification.  The CDC
                    generated for a particular impact is based
                    upon damage resulting from direct contact
                    only; it does not include induced damage.  All
                    CDCs are based entirely upon the procedures in
                    the SAE recommended practices document SAE
                    J224 MAR80.  

                    The CDC is a seven-character code used to
                    describe a field damaged vehicle.  Columns 1
                    and 2 (force direction), Column 3 (area of
                    deformation), Column 4 (specific longitudinal
                    or lateral area), Column 5 (specific vertical
                    or lateral area), Column 6 (type of damage
                    distribution), Column 7 (extent).

                    For the purposes of iCAR the main characters
                    of interest are in Columns 1 through 3.  iCAR
                    needs to know the force direction (either
                    through the improved PDOF or through the data
                    in Columns 1 and 2).  iCAR also needs to know
                    the plane of contact (e.g., front, back, left,
                    right, etc.).

D                   Location of midpoint of direct damage with
                    respect to vehicle center of gravity.

Delta V             Change of velocity.


L                   Length of damaged region (includes direct and
                    induced damage).

PDOF                Principal direction of force.  Sometimes
                    referred to as thrust.

UEW                 Undeformed end width.

WB                  Wheelbase.
