This workbook will cover all of the
modules in the Platinum version of REC-TEC. Problems will be shown using the Imperial system of
measurement. REC-TEC can work in
any Imperial/Metric (or hybrid) system and can be switched between systems at
any time. It will assist in becoming
familiar with the various modules, and show how the program can solve very
different, difficult, and complex problems. The workbook uses a step-by-step
approach to REC-TEC accident reconstruction. It is not intended to teach the basics of accident
reconstruction, but to assist the accident reconstructionist in solving
problems using REC-TEC.
Fundamentals of Traffic Crash
Reconstruction,
Volume 2 of the Traffic Crash Reconstruction Series by John Daily, Nathan Shigemura, and
Jeremy Daily, published by IPTM, is highly recommended as a basic tool
for learning the science and art of accident reconstruction.
Figure 1
Figure 1 shows
the new Help (F1) & Manual/Tutorial (F5) selections on
the upper navigation bar (October 2015). Both are 'module sensitive' in REC-TEC Platinum.
REC-TEC
BASICS
REC-TEC takes a modular approach to accident reconstruction problem
solving, just as reconstructionists have always done. Each problem is broken down into solvable components:
·
Determine
the primary objective of the investigation.
·
Break the
overall problem down into solvable components.
·
Combine the
individual answers into a unified solution to the problem.
With these steps in mind, we will begin to
solve problems using REC-TEC.
It is suggested that you work the
problems on your computer as we go through them in the workbook in order to
receive the maximum benefit from this workbook.
Navigating
the Program
Before we begin to work problems, it may
be beneficial to take an in depth look at the main screen and take a tour of
the many features to get a better understanding of the functionality of the
program. In addition to the new module
sensitive selections on the upper navigation bar, the F1 – F5 keys also
work from the Main screen. The F5
Key will call this document from the REC-TEC web site.
NEW *****
GLOBAL ENHANCED GRAPHICS (May 2014 Upgrade)
Figure
A
Figure A
displays the new "eGraphics" button on the Lower Navigation Bar. When the button shows eGraphics the new
graphics upgrades will replace the original graphics functions. Graphics and eGraphics are toggled using the
selection "Toggle Enhanced Graphics (Platinum)" on the Down Arrow
button to the right of the Graphics/eGraphics button as seen in Figure B.
Figure
B
eGraphics
consist of crosshairs that follow the cursor on selected graphics screens
throughout the program. Two or more
blocks will also appear with Time, Distance, Speed, or Lateral Distance
matching the crosshair position. The
crosshair position and data blocks can be "frozen" or
"unfrozen" using the [Ctrl] key. This allows the cursor to be moved for other purposes such as
clicking on the Report button to place the image in the report, or drawing on
the image using the right mouse button as in original Graphics.
Modules with the
enhanced graphics include:
·
Collision Avoidance Following Maneuvers
·
Collision Avoidance Turning Maneuvers
·
Time Distance Acceleration
·
Time Distance Deceleration
·
Time Distance Multiple Vehicles
·
Time Distance Omni
·
Time Distance (EDM)
eGraphics is a
Platinum Option only upgrade that also includes a unique new feature in the
Time Distance (EDM) module. When the
crosshairs are on the TD-EDM graphics, clicking on the left mouse button will
immediately capture the point on both curves where the vertical crosshair is
located and will place the corresponding Time, Distance, and Speed in the
center data blocks below the graphics.
As before, the
Data blocks below the Graphics screen can still be used to find and position a
set of crosshairs on the Graphics corresponding to a Time, Distance or
Speed. The new eGraphics permits using
the vertical crosshair to select a position on the either curve and get the
corresponding Time, Distance, and Speed information.
CONFIGURATION
(Table of Contents)
Figure
2
On the upper navigation bar of the main
screen, select Setup > REC-TEC (Figure 2) to call up the Configuration
screen (Figure 3). All problems will
assume the following configuration unless otherwise specified:
Figure
3
The preferences selected using the Configuration
screen (Figure 3) will be set every time the program is started. This screen may be called at any time to
change the preferences set at program start. Temporary changes can be made in
the various modules or by using the Graphics Icon (or drop-down) on the
main screen.
The configuration screen will set the
basic input/output displays throughout the program as well as which additional
programs REC-TEC will call
(word processors, drawing packages, etc.).
The F1 help files may be translated into many languages. Use the F7 key to pull up the HTML file from
the website and right clicking on the English version in order to use one of
the many Translation Accelerators now available.
Many display options can be set here as
the default, but can be changed temporarily from the Graphics icon on
the lower navigation bar.
Modules
REC-TEC consists of various modules that, by treating your
computer as a computer instead of a calculator, compute the answers for the
maneuver, not just a single formula.
Most modules offer iteration and graphics. Many offer animation and finite difference analysis. These tools
will assist the professional in analyzing the problem and help provide
confidence in the solutions. Many of
the modules will integrate with other modules, providing additional analysis
and support.
Upper Navigation Bar
(Table of Contents)
Opening a module – At the REC-TEC pull down menu (upper navigation bar
– left side), select Time - Distance then Acceleration - Deceleration
(Rate/Factor) from the submenu (Figure 4).
Figure
4
Note: Modules followed by an
asterisk are capable of generating an animation text file. These files can be imported into third-party
animation software capable of creating high-resolution animation using the X,
Y, and Z positions for each time key frame computed by REC-TEC. A list of these modules and what is required
is in the Manual > Overview Help file.
Click
on Acceleration - Deceleration (Rate/Factor) and the Time - Distance
Acceleration - Deceleration screen appears (Figure 5).
Figure 5
As an alternative, a file (or multiple
files) can be selected from the upper navigation bar Files > Open Single
File (Figure 6) or Files > Open Multiple Files.
Figure
6
This will call up a box showing all of
the files in the Folder selected.
Figure 7
Clicking on Open will call up the
Module and automatically open the file in the appropriate module (Figure 8).
Figure 8
If Open Multiple Files is selected, the
user may open multiple files in one or more modules. To end this process, click on the Cancel button in the file
display box.
Notice in Figure 8, on the lower
navigation bar on the right hand side the icon labeled AutoLoad. In Figure 8, AutoLoad is turned off (AutoLoad[Off]). When a module is exited, or the program is
exited, all modules save their current data to a file named “Lastfile”
with the appropriate extension for the particular module.
Caution – if multiple copies of the same module are opened with
different files, be sure to save the data as “named” files as the last module
to close will overwrite the other “Lastfile” in identical modules.
Files – Opening and Saving Files
Almost every module allows saving the
data to a file that can be re-opened later, redisplaying the original
computations. Each of these text files
carries an extension (.???) unique to a particular module. When a module is closed, the data (or lack
of data) in that module is automatically saved as Lastfile.(ext). If AutoLoad is set to [On], the file for the
module will open using this Lastfile.(ext) unless the module is opened by
selecting a particular named file.
Once a module is open, a file can be
opened at any time using the Open .EXT File button.
The Save .EXT File button will
save the data with a user selected name.
Other Files options are available which
call up text files produced by various modules for third party animations. Many popular movie (animation) formats can
also be called up using the Files menu.
Setup
The submenu > REC-TEC calls up the Configuration screen, which
can be viewed or modified.
The submenu > Reset
Defaults calls up the Configuration screen with
the default settings, which can be viewed or modified.
The (Figure 9) submenu > View permits the
user to independently view or hide the lower
(Icon) navigation bar and the Status bar at the bottom of the screen.
Figure 9
Figure 10 (Removed in 2015) - Functions Duplicated
on Lower Navigation Bar
Edit
(Figure 10) - (Functions duplicated on Lower Navigation Bar)
Figure 11
Tools (Figure 11)
·
Submenu >
Calculator: Windows Calculator
(Switches between Normal and Scientific).
·
Submenu >
Drawing Program: Set on
Configuration screen.
·
Submenu >
Word Processor: Set on
Configuration screen.
·
Submenu >
Contract (Recon-Attorney): Sample
contract.
·
Submenu >
Defaults & Rules of Thumb:
Collection of values.
·
Submenu >
Formulae: Formulae used in
program (two formats).
·
Submenu >
Glossary – (rsmck.com): Useful
AR glossary.
·
Submenu >
Hazmat Data: Hazmat information.
·
Submenu >
Railroad Information (rec-tec.com): Useful Railroad information.
·
Submenu >
Request for Production (RR): Sample
document (Railroad).
Figure 12
Vehicles (Figure 12)
·
Federal
Motor Vehicle Safety Standards (571)
·
Federal
Motor Carrier Safety Regulations (590)
·
NHTSA
Crash Database (Internet)
·
NHTSA
Recall Database (Internet)
Figure 13
Internet
- Useful
AR Internet Links (Figure 14)
- REC-TEC
Internet Links
- REC-TEC
Web Browser
- REC-TEC Version Check (Removed 2015 - Click on
License Name)
- REC-TEC
Upgrade (Download)
- Online
Articles
- Email
REC-TEC
Figure 14
Documentation (Figure 15)
- REC-TEC
- Email Information for License
- All
F1 Key (Help).PDF Files
- [F1]
key Program Overview or Help
- [F2]
key Finite Difference Analysis Overview
- [F3]
key Animation Overview
- [F4]
key Module Overview
- [F5]
key Inside REC-TEC (www.rec-tec.com)
- [F6]
key Same as [F1] key
- [F7]
key Same as [F1] key (www.rec-tec.com)
- [F8]
key Inside REC-TEC (PDF)
- [F9]
key REC-TEC Startup Guide (PDF)
- [F10]
key REC-TEC Version Check (www.rec-tec.com)
- About
Coordinate Systems (Diagram of
Coordinate Systems)
- Printing
Reports and Graphics (Figure 16)
Figure 15
Figure 16
Google
·
Calls Google
for Answers to many AR/Other questions
Name
·
REC-TEC
License (Figure 17)
Figure 17
Radio Button Functions
To the right of certain (Primary Output)
Speeds in selected modules there is a “Radio Button” that will transfer
the value of the Speed to the “Windows Clipboard” for transfer into
other modules within REC-TEC or anywhere else the user may select using
the Paste option after Right Clicking on the Mouse. This option
appears on the following modules:
Time Distance Multiple Surfaces (Initial
Speed)
Fall-Vault Airborne
Vault-Slide Integration
Yaw-Critical Speed of a Curve
Kinetic Energy
360 Linear Momentum (Impact Speeds)
At every entry point in the program calling
for an Acceleration/Deceleration Factor, there is a small round “Radio Button.”
Clicking the Radio Button will cause the Acceleration/Deceleration Factor
module to appear. Computations can be made for timed or measured vehicle tests
or for Drag Sled Pull weight divided by Sled weight. The user may
then transfer the result of the computation and Exit the module or Exit the
module without transferring a value.
Lower
Navigation Bar (Icons and dropdown menus) – See Figure 1
(Table of Contents)
·
Capture
Image – Captures REC-TEC
Image on Clipboard
o
Capture
Entire Screen
o
Capture
REC-TEC
o
Capture
REC-TEC (Active Form)
o
Capture
Active Window (time delayed capture)
o
Display
Captured Image (Displayed on REC-TEC Form)
o
Clear
Current Image
·
Print
Image – Prints REC-TEC
image to default printer
·
Report
Form – Sets link to
Word/WordPad/Adobe printer driver
o
Display
Help – Printing
o
Initiate
Document Link with Word (Integrated)
o
Initiate
Document Link with WordPad (Integrated)
o
Activate
PDF (Adobe) Document Spooler
o
Copy
Image to Report
o
Close
Document (Spooler to PDF Document)
·
Graphics
– Toggles Graphics
background color
o
Toggles
Background Color (Blue/White)
o
Graphics
Line Width = 1 (Session only)
o
Graphics
Line Width = 2 (Session only)
o
Graphics
Line Width = 3 (Session only)
o
Graphics
Line Width = 4 (Session only)
o
Graphics
Line Width = 5 (Session only)
·
Vehicle
Specs – Calls AutoStats
Lite from 4N6XPRT Systems
o
List of
4N6XPRT Vehicle Specs programs installed on computer (if any)
o
Canadian
Vehicle Specs (Windows Version)
o
Sisters
and Clones
o
Motorcycle
Specs (Internet)
·
Cycle
Windows – Cycles
(multiple) modules to foreground
o
Cascade
o
Tile
Horizontally
o
Tile
Vertically
o
Arrange
(Icons)
o
Minimize
All
o
Restore
All
o
Close All
·
AutoLoad
– Toggles AutoLoad[On/Off]
o
Save
Change
o
AutoLoad
– ON
o
AutoLoad
– Off
Module
1: Time - Distance – Acceleration-Deceleration
(Rate/Factor)
(Table of Contents)
Overview: This module
computes Acceleration/Deceleration factors and rates based on supplied
information.
At the REC-TEC pull down menu, select Time - Distance >
Acceleration-Deceleration (Rate/Factor) and the Time - Distance -
Acceleration-Deceleration (Rate/Factor) screen appears (Figure 18).
Figure 18
Input
Data
This module has four data inputs (No “required”
inputs)
- Initial
Speed
- Final
Speed
- Distance
- Time
Two or three inputs are required to
generate a solution.
·
If Distance and Time inputs are used, the module
will compute a solution. If a Speed input is added, the module
solves for the unknown speed input.
·
If a Distance and a Speed input greater than zero is
used, the module will compute a solution.
If Time or a second Speed input is added, the module
will solve for the remaining unknown.
·
If two Speed inputs are
used, either Time, or Distance is required. The module will solve for the remaining
unknown.
Example 1: A vehicle
accelerates at a uniform rate traveling 100 feet in four seconds.
1. What is the
acceleration factor?
2. What is the
acceleration rate?
3. What is the
final speed? Is there a way to
determine the final speed with the information given?
Figure 19
Example 2: A vehicle
accelerates from 20 M/H at a uniform rate traveling 100 feet in three seconds.
4. What is the
acceleration factor?
5. What is the
acceleration rate?
6. What is the
final speed?
Figure 20
Example 3: A vehicle
decelerates to a stop at a uniform rate traveling 100 feet in three seconds.
7. What is the
deceleration factor?
8. What is the
deceleration rate?
9. What is the
initial speed?
Figure 21
Figure 22
Figure 22 shows the Finite Difference
Analysis menu for the Acceleration/Deceleration factor.
Figure 23
Figure 23 shows the results of the Finite
Difference Analysis. This analysis is
for the Acceleration (or Deceleration) factor only. It does not include the speeds unless they are part of the
computation.
Iteration and Finite Difference Analysis
Iteration (table generation) is available in all versions of
REC-TEC and is almost
self-explanatory. It will be demonstrated
in the Time - Distance Single Surface Deceleration, 360 Linear Momentum, S-CAM
Air Brake and other modules that may represent unique variations on the basic
iteration model.
Finite Difference Analysis (FDA), which computes an “Uncertainty Level” based on a specific range of
the variables within a formula, is restricted to the Platinum Version of the
program. A general explanation of the
principles of FDA is called up by using the F2 key from any module offering
FDA. FDA will be demonstrated in the 360
Linear Momentum, S-CAM Air Brake and other modules that may represent unique
variations on the basic FDA model.
SAE paper 2003-01-0489 Evaluating Uncertainty in Accident
Reconstruction with Finite Differences by Wade Bartlett
and Al Fonda compares Finite Difference Analysis with the “Monte Carlo” type of
computations done by various high-powered statistics programs on the market.
For the same given ranges of the variables involved, the answers are identical.
Example 4: A 45-pound
drag sled has a pull weight of 33 pounds.
Select Deceleration (Sled) – this selection is made from the
screen shown in Figure 21.
10. What is the
deceleration factor?
11. What is the
deceleration rate?
Figure 24
Figure (24B)
Figure (24B)
shows the screen, as it would appear if it were called up using the new “Radio
Button” feature already described above.
The “factor” can be transferred automatically to the input on the
calling module or this page can be exited without transferring.
Module
2: Time - Distance – Acceleration
Single Surface
Overview: This module computes detailed information on the Speed,
Distance and Time of a single acceleration event.
At the REC-TEC pull down menu, select Time - Distance >
Acceleration - Single Surface and the Time - Distance - Acceleration screen appears (Figure 25).
Figure 25
Required Input Data:
Acceleration Factor (fa):
The percentage of gravity used to accelerate the vehicle. The acceleration factor is entered into the
program as a decimal value representing a percentage of gravity available to
accelerate the vehicle.
Example 1:
The vehicle has an average acceleration factor of .25 “g” during the
maneuver.
1.
How fast was
the vehicle traveling at the end of the acceleration if it started from a full
stop and accelerated for 200 feet?
2.
How long did
the acceleration take?
Solution: Enter into the module the required data:
- Acceleration Factor (.25)
- Initial Speed (0)
- Distance (200)
With this information, the final speed is computed at 38.6898 M/H
(question # 1) and a time of 7.049 seconds to accelerate from a full stop
(question # 2) as illustrated in Figure 26.
Figure 26
Example 2:
3.
How fast was
the vehicle traveling at the end of the acceleration if it started from 20 M/H and
accelerated for 200 feet?
4.
How long did
the acceleration take?
Figure
27
With this information, the final speed is computed at 43.5534 M/H
(question # 3) and a time of 4.2913 seconds to accelerate from 20 M/H (question
# 4) as illustrated in Figure 27.
Example 3:
5.
How fast was
the vehicle traveling at the start of the acceleration if it accelerated for
200 feet to a final speed of 60?
6.
How long did
the acceleration for the 200 ft. take?
7.
How long did
the acceleration take if it was from a full stop to 60 M//H?
8.
What was the distance
covered in Question 7?
Figure 28
With this information, the initial speed is computed at 45.8595
M/H (question # 5) and a time of 2.5763 seconds to accelerate for 200 ft. to a
final speed of 60 M/H (question # 6) as illustrated in Figure 28.
The time from full stop to 60 M/H is computed to be 10.9316
seconds (question # 7) and the total distance is 480.9937 feet (question # 8)
as illustrated in Figure 28.
Iteration and Finite Difference Analysis
Iteration (table generation) is available in all versions of
REC-TEC and is almost
self-explanatory in nature, it will be demonstrated in the Time - Distance
Single Surface Deceleration, 360 Linear Momentum and the S-CAM Air Brake
modules, as they each represent unique variations on the basic iteration model.
Finite Difference Analysis (FDA), which computes an “Uncertainty Level” based on a specific range of
the variables within a formula, is restricted to the Platinum Version of the
program. A general explanation of the
principles of FDA is called up by using the F2 key from any module offering
FDA. FDA will be demonstrated in the
360 Linear Momentum and the S-CAM Air Brake modules, as they each represent
unique variations on the basic model demonstrated in the Time - Distance Single
Surface Deceleration, module.
Module
3: Time - Distance – Deceleration
Single Surface
(Table
of Contents) (Table of
Contents)
Overview: This module computes detailed information on the Speed,
Distance and Time of a single deceleration event. If lateral information is
input, the module also computes detailed swerve and swerve-and-return data.
At the REC-TEC pull down menu, select Time - Distance >
Deceleration - Single Surface and the Time - Distance - Deceleration screen appears (Figure 29).
Figure
29
Required
Input Data
Coefficient
of Friction – “Mu”: The coefficient of friction is defined as
the percentage of gravity developed at the tire-road interface for acceleration
(deceleration). The coefficient of
friction is entered into the program as a decimal value representing a
percentage of gravity available to decelerate the vehicle.
Grade – Grade is the rise or fall of the
roadway. It is either a negative
downhill grade or a positive uphill grade and is dependant upon your direction
of travel. You may often hear it
referred to as the “slope” of the road.
Grade is determined by the ratio of the rise of the roadway divided by
the run or length of the measurement. It is the tangent of the angle.
The Grade of the roadway is entered into
the program using a positive uphill or negative downhill decimal value. If no entry is made, the module treats the
grade as zero.
Braking
Percentage – the braking
efficiency of the vehicle is a determination of how much of the entire weight
of the vehicle is being overcome by the brake force generated at the
wheels. As the vertical weight at each
brake point increases, a limit is reached when the components of the brake
assembly will no longer generate enough force to overcome the rotational torque
of the wheel. This limit is dependant
upon the vertical weight component on each wheel and the overall mechanical
condition of the brake components.
Braking efficiency is entered in the
program as a whole number percent value as opposed to a decimal value. Full braking on all wheels is entered as 100
(100%).
Example 1: A
vehicle skids 47 feet before striking a pedestrian crossing the roadway. It continued for an additional 20 feet
before coming to a complete stop. An
accelerometer was used to conduct skid tests and it was determined that the
coefficient of friction of the roadway was 0.73. The grade at the accident site was a negative 2% and the crash
vehicle had a overall braking efficiency of 70%.
- How
fast was the vehicle traveling at impact with the pedestrian?
- How
fast was the vehicle traveling when the driver first applied the brakes?
- How
long did it take the vehicle to skid to a stop?
- How
long did it take the vehicle to skid to impact with the pedestrian?
- If
the vehicle would have had 100% braking, would the collision with
pedestrian occurred?
Solving
the problem
Step
1: Determine from the problem what data
is available for input into the module
- Distance of skid to impact: 47 feet
- Distance of skid after impact: 20 feet
- Total distance of skid: 67 feet
- Ending speed/velocity: 0 mph
- Coefficient of Friction: 0.73
- Grade:
-0.02
- Braking efficiency: 70 %
- Optimum braking efficiency – 100%
Step
2: Enter into the module the required
data:
- Coefficient of Friction
- Grade at crash site
- Braking efficiency
Figure
30
Solution: This module requires two of the following four variables to reach
a solution.
- The
beginning speed/velocity,
- The
ending speed/velocity,
- The
distance of skid,
- The time
of the skid.
From the information given, we have two
known values that can be used to determine a solution and answer the general
questions that may be raised during the normal course of our
reconstruction. We know that the vehicle skids to a stop and therefore have an ending
speed/velocity of 0 mph. We also know that the vehicle skids 47 feet
pre-impact, 20 feet post-impact for a total skid distance of 67 feet. Using these two known values we can answer
Question 2 and Question 3 of our problem.
Step
3: Enter 67 feet as the distance of
skid to a stop and 0 miles per hour as the final speed of the vehicle.
With this information, the initial speed is computed at 31.3795
M/H (question # 2) and a time of 2.9115 seconds to skid to a full stop
(question # 3) as illustrated in Figure 31.
Figure
31
Question #2 concerning the initial speed of the vehicle (31.3795
M/H) and question #3 about the time to decelerate to a stop (2.9115 seconds),
have now been answered. The program has
computed the speed at the start of the deceleration as 31.3795 M/H and while
the reconstructionist would never use a four decimal point answer for the
initial speed in testimony, this is our computed initial speed for further
computations.
Enter the initial speed/velocity of 31.3795
M/H and the distance to the pedestrian of 47 ft as known values.
Figure
32
The program has now computed the answers
to question # 1 (17.1444 M/H) and question # 4 (1.3208 seconds). The only question left is #5.
By entering 100 for the percent of
braking, we find that a distance of 46.3337 feet is required to come to a full
stop and that at 47 feet the vehicle would be traveling at –3.7629 M/H. The
collision with the pedestrian would not have occurred.
Figure
33
Figure 34
The Formulae* button will bring up
a screen showing the formulae required to compute the two missing variables
(Figure 34).
The Graphics button will show the Speed
versus Time and Speed versus Distance graphs.
In Figure 35, the curves are shown for 70%
braking.
Figure
35
The Animation button will display the
deceleration curve for the Time or Distance entered in the blocks in Figure
36. Entering a number greater than 1
will display the animation in slow motion.
Figure
36
Notice that in Figure 37 the 47 foot mark is shown as a
small circle on the curve.
Figure
37
This module has an optional input –
Lateral Distance. This distance could
be the width of a lane or the distance the vehicle must move laterally in order
to miss the object. This module
computes the lateral movement based on the full friction value of the
coefficient of friction. The following
figures will show a Lateral Distance of 12 feet. The additional data the module
is able to compute is displayed in Figure 38 and described more fully in the
Help file available by using the F1 key while in this module.
Figure
38
Figure 39
The Formulae* screen now displays
the basic formulae and computations for the distances required for the Swerve
and Swerve & Recover Distance computations as shown in Figure 39.
Swerve-No Return shows what would happen if the vehicle
were placed in a maximum rate change of direction using the coefficient of
friction (modified for grade). This is
the same as using a .71 G turn using the numbers in this example. This would allow the vehicle's center of
mass (or any given point of reference) to pass 12 feet laterally from the
initial path of travel. This would NOT
have the vehicle headed on a parallel path; it would be headed in a different
direction (like off the road and into the boonies?). If the vehicle were brought back to a parallel path, the distance
and time would be doubled as would the total lateral distance.
Swerve and Return shows what would happen if the vehicle
were placed in a maximum rate change of direction using the coefficient of
friction (modified for grade) with an immediate change to a maximum rate change
of direction in the opposite direction, at the optimum point to accomplish the
maneuver. This allows the vehicle's center of mass (or any given point of
reference) to pass 12 feet laterally from the initial path of travel. This has the vehicle headed in a parallel
path. This is a “lane change” maneuver.
Critical Turnaway is a Speed at which the Distance
Slide to Stop and the Distance required for the Swerve (or Swerve
and Return) maneuver are identical. Critical Turnaway is a Speed at
which two distances are identical. It is similar to a point of no return.
Critical
Turnaway Distance – Distance
for both Slide to Stop and Distance required for the maneuver
Critical
Turnaway Time – Time
required to stop from the Initial Speed
Critical
Turnaway Speed – The Speed
at which the Distance Slide to Stop and the Distance required for the Swerve
(or Swerve and Return) maneuver are identical
The enhanced Animation is shown in Figure
38. The animation (real time or slow
motion) can be paused and continued using the Spacebar. Moving the mouse over the graphics or
animation while depressing the left mouse button enables drawing on the
screen. The right mouse button will
cause a re-draw.
Figure 40
Iteration and Finite Difference Analysis
The Iteration/Finite Difference
Analysis Menu button calls up a menu (Figure 41) that will generate
iteration tables and initiate a Finite Difference analysis based on the values
entered as the Minimum and Maximum values of the variables. See additional information on FDA using the
F2 key.
Figure 41
In Figure 42, the appropriate variables
are ranged and the desired interval for the iteration has been entered.
Figure 42
Figure 43 shows the table generated for
the drag factor (adjusted for braking) solving for the Initial Speed keeping
the Distance and Final Speed constant as selected in Figure 42.
Figure 43
Figure 44
Figure 44 shows a finite difference
analysis for the final speed (speed at contact with the pedestrian) based on
ranging the Drag Factor, Distance and Initial Speed generating an uncertainty
value of 6.064 M/H.
Module
4: Time - Distance – Multiple Vehicle
Overview: This module computes comparative data
for two vehicles in two individual acceleration, deceleration or constant
velocity events and offers animation of the maneuver.
At the REC-TEC pull down menu, select Time - Distance > Multiple
Vehicles and the Time
Distance Multiple Vehicles
screen appears (Figure 45).
Figure 45
Required
Inputs
The required
input data depends on the user-selected maneuver for each vehicle or
object. Single-Surface Acceleration and
Single-Surface Deceleration modules can be referenced for information on the
required input data for these maneuvers.
Constant Velocity will require the Initial Speed and the
Final Speed as inputs, and they must be identical.
Example
1:
Vehicle 1 decelerates from 60 miles per hour to a final speed of 15
miles per hour (striking vehicle 2).
The Mu value is 0.6 and the grade is zero. The braking is 100%.
Vehicle 2 accelerates from 7.5 miles per hour to a final speed of 30
miles per hour (striking vehicle 1).
The acceleration factor is 0.2.
This module allows some unique options
such as CLOSURE, which can help investigate the sight triangle between
the two units involved. Either vehicle
can be studied for any time or distance before the event in question, be it a collision,
stop, or any point under consideration
For this problem, two vehicles will be
taken into collision. Tables can be
generated to study what happened before impact. With the ability to look at units in any combination of
acceleration, deceleration, or constant velocity, any situation can be
analyzed.
This section can be used to analyze
vehicles, or vehicles and pedestrians in collision. This section can also be used to study the effects of different
values for the same vehicle (side by side).
Figure 46
1.
How fast was
Vehicle #2 going when vehicle #1 was 1.5 seconds from impact?
2.
How far from
impact was Vehicle #1 when Vehicle #2 was 5 seconds from impact?
Figure 47
If the vehicles end together at Time = 0,
and a .5 second time interval is used, a speed table can be created that will
answer the question.
The answer to
question #1 is 23.4136 M/H (Figure 48)
Figure 48
The answer to
question #2 is 327.267 feet. (Figure 48)
3.
When Vehicle
#2 was 25 feet from impact, what was the speed of vehicle #1?
Figure 49
The answer to
question #1 is 22.8246 M/H (Figure 49)
The Closure button computes
data on the triangle using the two vehicles and impact.
Figure 50
The Execute button displays
(Figure 51) the triangular relationship defined by the angles entered in the
blocks on Figure 50.
Figure 51
The Graphics button (Figure 46) brings up a menu (Figure 52)
controlling the graphics curves (Time or Distance and the values involved)
displayed on the screen (Figure 53).
Figure 52
Figure 53 shows the time curves for the greater
time of the acceleration.
Figure 53 (Time)
Selecting Distance on the menu shown on
Figure 54 and increasing the total distance from 187.8881 feet to 250 feet
shows the graphics on Figure 55.
Figure 54
Figure 55 shows the distance curves for
the increased distance of 250 feet.
Figure 55
The Animation button (Figure
46) brings up a menu (Figure 56) controlling the way animation is displayed on
the screen.
Figure 56
After engaging the options of choice on
this menu (Figure 56), the Execute button will initiate the animation (Figure
57).
Figure
57
Example
2:
Vehicle 1 decelerates from 60 miles per hour to a final speed of zero.
The drag factor is 0.72. Vehicle 2
decelerates from 60 miles per hour to a final speed of zero. The drag factor is
.61. Vehicle 2 is "Trailing"
100 ft. behind Vehicle 1. Vehicle 2 has
a 1.5 second perception reaction time (PRT) when Vehicle 1 brakes. There is no grade and the braking is 100%
for both vehicles.
Figure
58
Once the problem is setup up, select
Animation. Select "From
Start" and use the parallel format.
Answer the remaining questions using the information listed above. Select compute for TIME.
Figure 59
Figure 60
Do the vehicles hit? At what speed?
Vehicle 1______________________
Vehicle 2______________________
Example
2A: How would
the answer change if the PRT was 2 seconds and the trailing distance was 75
feet?
Do the vehicles hit? At what speed?
Vehicle 1______________________
Vehicle 2______________________
Example
2B: How would
the answer change if the PRT was 1 second and the trailing distance was 150
feet?
Do the vehicles hit? At what speed?
Vehicle 1______________________
Vehicle 2______________________