Suzy B Software 2/Suzy B Software CD-ROM 2 (1994).iso/adult_ed/smct/smct.asc

Text File | 1995-05-02 | 8KB | 159 lines

                             S.M.C.T.
                  Skid Mark Calculation Template

                  (C) 1987 -- Michael K. Shallop

This program,  although copyrighted,  is released into the  public
domain,  and may be distributed and modified as long as credit for
           the original program is given to the author.

Calculation   data  was  obtained  from  the   "Traffic   Accident
Investigation Manual" written by J.  Stannard Baker,  (C) 1975  by
  The Traffic Institute, Northwestern University, Evanston, Il.

The  program was written and compiled in GFA Basic,  (C)  1986  by
                        GFA-SYSTEMTECHNIK


INTENTS AND PURPOSE:

     I wrote this program in one sitting on April 12,  1987, in an
attempt to teach myself GFA Basic.  (Which, if you do not own, you
most  certainly  should!)   For  the past 10  years  I  have  been
actively involved in law enforcement and for 6 years have been  an
accident  investigator  for  a  municipal  agency.    In  1981,  I
attended an advanced accident investigation school that was taught
by the NW Traffic Institute.  Since then, I have been certified in
municipal,  district, federal, and civil court rooms as an "expert
witness" in accident investigation and reconstruction.  To date, I
have  investigated over 1400 vehicle collisions including  several
fatalities.   I have investigated car-train,  car-cycle,  car-car,
car-pedestrian,  car-structure,  and car-truck accidents.  While I
feel that there are several areas within this specialized realm in
which to improve myself,  I do feel that I possess more  knowledge
and experience than the average officer on the street.
     This program, as stated earlier, was written as a programming
exercise.  I do not plan to use the program within the scope of my
profession,  although  I  certainly could if I  so  desired.   The
intent  of the program for the average user is for  entertainment.
While you may not understand some of the concepts used in  writing
this  program,  you may have fun experimenting with  it.   Imagine
knowing how fast you are travelling in a given environment.  This,
and  only  this,  was the reason that the program  was  developed.
This  program  was not intended for the use of  reconstruction  in
motor vehicle collision investigation.

DEFINITIONS:

     The  speed of vehicle may be calculated through the use of  a
linear algebraic equation.  Using three variables, the length of a
skid of a vehicle, the coefficient of friction (or drag factor) of
a roadway,  and of course,  the speed of the  vehicle.  Naturally,
when  two  of  the three variables are known,  the  third  may  be
determined in the equation along with the use of a constant.
     The coefficient of friction is defined as the amount of force
necessary  to  move one pound of vehicle weight  to  overcome  the
resistance of gravity.  This will almost always be a decimal value
of less than 1.0.   In simpler terms,  this can also be called the
surface  resistance  between  the tire  and  the  roadway.   Since
vehicle  weight is not a factor,  then this equation will work  as
well for a pick-up truck as it would for a VW beetle.
     The  skid  distance is the length that  the  vehicle  skidded
before coming to a stop,  or striking another object.   Skids left
after  a  point  of impact are NEVER  used.   Opposing  force  can
accelerate as well as deaccelerate a vehicle.   When you work with
skid marks,  you are working with absolute MINIMUMS.   Normally  a
vehicle  will leave skid marks of varying distances.   Always  use
the  longest measurement in your calculations.   I know that  this
sounds contradictory to what was just said, but a vehicle skidding
from the moment of where the first skidmark was first left is what
is to be measured.
     The constant in the formula is the square root of 30.  If you
are  using pen and paper,  use 5.5 as your  constant.   The  basic
speed calculation is:   Vehicle Speed = SQR(30 times (distance  of
skid times the coefficient of friction )). Sp=(sqr(30*(df*sd)).
     I  use a reference point of 30 miles per hour to  verify  the
accuracy of my equations.   If a vehicle leaves 42 feet of skid on
a roadway with a c.o.f.  value of 0.72, then the speed will always
be calculated as 30 mph.

INSTRUCTIONS FOR USE:

     The  menu  bar  shows  several  choices:   Options,  Roadway,
Surfaces,  Grade, and Skid.  Using these in their correct order as
they  appear  from  left to right will result  in  a  correct  and
accurate  determination of speed.   Using them out of  order  will
result  in an inaccurate speed computation.   ALWAYS PROCEDE  FROM
LEFT TO RIGHT!

Option

     You  have the option under this menu heading of  setting  the
coefficient of friction (C.O.F.),  or the length of skid.  Use the
C.O.F.  option ONLY if you do not use the options available  under
the other menus.   The skid value MUST ALWAYS BE SET BY YOU!   The
program does not know how far your vehicle skidded, therefore, you
must  supply this number.   Enter it as requested in the  program.
The  program will alert you if you try to calculate without  first
doing  this.   The Calculate option will return an ALERT box  that
will give you an interger value of the speed of the vehicle.   You
may  use the same skid length without having to reset it from  run
to run.   This is to examine how various factors affect the  speed
of the vehicle.   Quit will return you to the desktop.   You  will
not get a "Are You Sure?" option.

Roadway:

     Use this to set the surface of the road that the vehicle  was
travelling  upon.   While  not all of the available  options  were
listed,  there  should  be  enough here to  satisy  any  available
condition.   This option will initially set the coefficient value.
All other options will modify this value.  USE THIS OPTION FIRST!

Surfaces:

     This  is  what is on the roadway.   In the  broadest  general
sense.    Some of these will just modify the c.o.f.  value, others
will competely change it.  USE THIS SECOND.

Grade:

     This  is  the slant of the road.   The values  assigned  here
range from 0.05 to 0.15.   This is interpreted as 5 feet rise  per
hundred  feet to 15 foor rise per hundred feet.   The source  code
may be altered to show really steep grades.  This will add a value
to the established c.o.f.  USE THIS THIRD.

Skid:

     This  is the final option for you to choose.   All  of  these
values will modify the established c.o.f.   If your "vehicle"  did
not skid on all four tires,  then it will take you longer to  stop
than  if all four brakes were working correctly.   The  motorcycle
option  adjustes the c.o.f.  value to show that a cycle's  braking
efficiency  is only 60% that of normal.   You cannot lock  up  the
front  tire  of  a  motorcycle for longer  than  13  feet  without
crashing.   At any speed.    Therefore,  since 60% of the vehicles
weight is over the rear tire,  the c.o.f.  value must be  modified
accordingly.  USE THIS OPTION LAST.


SUMMARY:

     Well,  there you have it.   I hope you find some use in  this
program.   Most people will be entertained by it.   I welcome  any
comments or questions.  Feel free to make any alterations that you
see  fit.   Please give me credit for the program.   I have  spent
many  painful years learning this area of accident  investigation.
Brother  officers  can  contact me for other  programs  that  will
accomplish more than the basic speed calculations.   Yaws,  flips,
vaults, determining drag factors and skid distances, et cetera can
be easily written now that I have been broken in to GFA basic.
     I  may be reached electronically one of two  ways:  My  GEnie
mailing  address is M.SHALLOP  -- I may also be contacted  on  the
M*A*S*H* BBS at [phone] under the handle of "Tai-Pan".

                        Michael K. Shallop
                          April 12, 1987