R E C T E C
P R O F E S S I O N A L
Training Manual and Tutorial
P.O. BOX 561031
ROCKLEDGE, FLORIDA 32956-1031
Copyright George M. Bonnett, JD 2018 All Rights Reserved
The information contained in this manual is based to the best of REC-TEC LLCs knowledge on viable although innovative practices in the investigation of incidents as applied to vehicular collisions. However, neither REC-TEC LLC nor the author assumes any liability in connection with the use of this material. Every acceptable procedure may not have been presented and some circumstances may require additional or substitute procedures. Also, statutes, ordinances and organizational policies differ widely and wherever these are in conflict with the information contained herein, the former should govern.
Copyright © 2018 by George M. Bonnett, JD. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, to include photocopying and recording, or by any information storage and retrieval system, without prior permission in writing from the author.
When Viewing This Document
Select View then Text Size or Zoom in your Browser (or the Zoom feature in the lower right corner of most Browsers) to change the way this manual appears on the screen.
This entire document was assembled using Microsoft Word, Screen Hunter 6 (free) and REC-TEC Platinum software. All screen shots were captured using REC-TEC Platinum Software, [Alt PrtSc], or Screen Hunter 6 for Screens with drop down or sub menus.
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 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 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.
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 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.
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.
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:
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.
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.
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).
Click on Acceleration - Deceleration (Rate/Factor) and the Time - Distance Acceleration - Deceleration screen appears (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.
This will call up a box showing all of the files in the Folder selected.
Clicking on Open will call up the Module and automatically open the file in the appropriate module (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.
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.
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).
Vehicles (Figure 12)
· Federal Motor Vehicle Safety Standards (571)
· Federal Motor Carrier Safety Regulations (590)
· NHTSA Crash Database (Internet)
· NHTSA Recall Database (Internet)
Documentation (Figure 15)
· Calls Google for Answers to many AR/Other questions
· REC-TEC License (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)
Yaw-Critical Speed of a Curve
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.
· 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 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
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).
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?
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?
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 22 shows the Finite Difference Analysis menu for the Acceleration/Deceleration factor.
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 (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.
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).
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:
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.
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?
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.
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?
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 (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.
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).
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%.
Solving the problem
Step 1: Determine from the problem what data is available for input into the module
Step 2: Enter into the module the required data:
Solution: This module requires two of the following four variables to reach a solution.
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.
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.
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.
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.
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.
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.
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.
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.
In Figure 42, the appropriate variables are ranged and the desired interval for the iteration has been entered.
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 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.
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).
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).
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?
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)
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?
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.
The Execute button displays (Figure 51) the triangular relationship defined by the angles entered in the blocks on Figure 50.
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).
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 55 shows the distance curves for the increased distance of 250 feet.
The Animation button (Figure 46) brings up a menu (Figure 56) controlling the way animation is displayed on the screen.
After engaging the options of choice on this menu (Figure 56), the Execute button will initiate the animation (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.
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.
Do the vehicles hit? At what speed?
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?
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?