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Appendix G
USER GUIDE SOFT WARE HELP SCREENS
This appendix documents the applied Help Screens included in the TWEET software, in order to
assist NCHRP Project 20-34 panel members with their understanding of the developed User
Guideline documentation. While much of the text shown here is similar to that in the Chapter 3
User Guide, it is more detailed in certain areas, e.g., the Pavement Analysis explanation, due to
the fact that software users may not necessarily have access to the project documentation.
Truck Weight Enforcement Effectiveness Too! 1.2
Contents
Welcome to the Truck Weight Enforcement Effectiveness Tool, or TWEET, Version 1.2. The fol
lowing help topics are available. Click on Overview for a general explanation of this software; this
is a good starting point for the new user. Otherwise, please select one of the following topics.
General Topics
Overview
General explanation of the TWEET software and how to use it to determine the effectiveness of a
weight enforcement program
Input Overview
A step by step explanation of the process of entering the program's input
Outout Overview
A step by step explanation of the program's output, including how to interpret the data tables, print
them, etc.
Specific Topics
In addition to the general topics above, some more specific topics are provided to aid the user at
each steD of the Droaram. The Drooram uses a series of dialogs: each of the tonics below corre
, , _ , _ _ . .
spends to one of these dialogs. (Please note that each of these topics can also be accessed by
oressina the HelD button in its respective dialog: e.a.. the Select Units Dialoa toDic can be viewed
which running the TWEET software by pressing the Help button in the Units dialog itself.)
Select Units Dialon
Lenal Weight Limits Dialog
Data File Format Dialon
Enforcement Condition Dialon
Number of Data Files Dialoq
Select Data File Dialon
Pavement Analysis Dialoq
Percentane of Overweight Trucks Dialog
Truck Classification Data Dialon
Breakdown of Violations Dialogs
Severity of Violations Dialoq
1
Appendix G
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ESAL Data Dialog
Data File Conversion Dialon
~orcement Condition Dialon
Same ~ Mu Lie Dia ~
Pavement Effects Analysis Dialog
.
Overview
To dive right into the exciting world of truck weight enforcement, click on Quick Start
TWEET is a software application designed to aid users in determining the effectiveness of user-
specified truck weight enforcement policies. It worlds by reading WIM data which has been col-
lected under different enforcement conditions, and allowing the user to compare the data from
each condition to determine the most effective method of enforcement.
This software presents the user with a variety of "dialog boxes", i.e., pop-up screens which en-
able the user to provide required inout to run the software. The software is designed to be user
~ .. . . .. ... .
trendy, e.g., In most cases the user will simply press the "Next" button to continue operation.
To start a truck weight enforcement analysis, press the start analysis button in the program's main
window. There are three discrete steps to the analysis process:
.
User Input
This phase of the programs requires the user to enter such information as the type of units the
program is to use (English or Metric), the format of the data files used, etc. See Input Overview
for more information.
Calculation
In this phase of operation, the program performs the necessary calculations on the data, including
percentage of violations, Bridge Formula calculations, etc. This is done entirely automatically by
the program, and the user need not be concerned with this part of the program.
During calculations a graphical percentage meter is displayed.
Output
In this phase of the program, the calculated data is displayed to the user. The data is displayed
on-screen in a series of dialog boxes, each of which can be printed by the user. The program will
automatically display the calculated values after finishing the calculations. Once the program has
performed the calculations, the output can be viewed again by pressing the View Results button
on the main window. See Output Overview for more information.
Input Overview
The first main phase of the program's operation is to accept input which defines how the calcula-
tions are to be performed. The input phase consists of a series of dialog boxes which ask you to
enter certain values. Below is a short list of each input dialog in the order you will encounter them.
Please select one of the following topics:
Select Units Dialon
Legal Weight Limits Dialog
Data File Format Dialog
Enforcement Condition Dialog
Ap,6dnd~x G
2
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Number of Data Files Dialog
Select Data File Dialog
Pavement Analysis Dialon
Data File Conversion Dialog
Output Overview
After the program has completed its calculations, which are done without any action on the user's
part immediately following the input phase, it displays the output. Each output dialog displays its
data, and has four buttons at the bottom of the window. These buttons are:
_ . _ . .. . .. .
"NEXT" Closes the current output dialog and displays the next output dialog.
Cancel Closes the current output dialog and returns the user to the main window immediately.
Print Prints the information in the dialog on the user's printer.
Help Takes the user to the appropriate page in this help system. For example, if you were using
the ESAL Data dialog and you pressed its Help button, the ESAL Data Dialon help topic would be
displayed.
Below is a list of the output dialog help topics. Select the one which corresponds to the dialog
with which you need help.
Percentage of Overweight Trucks Dialog
Truck Classification Data Dialog
Breakdown of Violations Dialogs
Severity of Violations Dialog
ESAL Data Dialoq
Data File Conversion Dialon
comparison of Enforcement Condition Dialog
Sampling Guide Dialon
Pavement Effects Analysis Dialon
Select Units Dialog
This dialog asks you to select the system of units of measure to be used by the program. The
choices are the English (feet, pounds) or Metric (meters, kilograms) units. Simply click on the radio
button which denotes the choice you would like to use, and press ~Next".
Number of Data Files Dialog
This dialog asks you to enter the number of data files you wish to combine for studying a particular
condition. For example, if you collected three data files for the condition which is under study, type a
"3" in this dialog.
3
Appendix G
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Enforcement Condition Dialog
This dialog allows you to enter the information about both of the enforcement conditions. For each
condition, you will be asked to enter the following information:
Name You may give the condition any name you want. Names do not have to be unique (you can
name all the conditions "condition" if you like) although it is advisable that they are unique.
Location This field allows you to enter a location from which the data was collected. This field may
be optionally led blank.
start Date This field asks you to enter the starting date of the study; it too may be led blank.
End Date This field asks you to enter the ending date of the study; it too may be left blank.
Legal Weight Limits Dialog
The Set Legal Weight Limits dialog asks you to enter the maximum allowable weights as defined by
your local laws. There are three fields presented: Gross Weight, Single Axle Weight and Tandem
Axle Weight. The Gross Weight is the total weight of the entire vehicle; the Single Axle Weight is the
weight of one axle of the vehicle; the Tandem Axle Weight is the combined weight of a set of axles
that are within a certain distance of each other. The defaults in this dialog should be adequate for
almost all users. Modification of these defaults may be necessary depending upon prevailing legal
regulations.
-
Pavement Analysis Dialog
INTRODUCTION
One of the basic premises of truck weight enforcement is that there will be a net increase in
pavement life (reduction in the rate of pavement deterioration). The applied method makes use of
an MSHTO design procedure providing for the frame input to design to be in terms of
accumulated (or projected) 18,000 lb. equivalent single axle loads (ESALs).
In their approach, AASHTO uses the definition: "Load equivalency factors represent the ratio of
the number of repetitions of any axle load and axle configuration (single, tandem, tridem)
necessary to cause the same reduction in Present Serviceability Index (PSI) as one application of
an 18-km single axle load." Thus, an axle load with an 18-km equivalency of 2.5 could be
considered to be 2.5 times more damaging than the 1 8-km loading.
The general approach, is to determine the cumulative ESALs a given pavement is capable of
sustaining before its serviceability is reduced to an unacceptable level, i.e., the design load
capacity. Then, the traffic stream using that pavement is analyzed both before and after
enforcement efforts are implemented to determine the effects of that enforcement on daily ESALs
generated by the stream. Finally, the daily ESALs before and after enforcement are used to
determine the estimated times (before and after enforcement) required to consume the load
capacity.
Appendix G
4
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DETERMINATION OF FLEXIBLE PAVEMENT STRUCTURAL NUMBER
The structural number (SN) is a measure of relative pavement strength and is defined as:
SN = a,h, + a2h2 + ~
where:
-
- - ~ ajh` Equation D1
from the top down, hi is the thickness of layer one which has a layer coefficient of a,, h2
is the thickness of layer two which has a layer coefficient of a2, etc. Table D1 is a
tabulation of layer coefficients for materials typically used in flexible pavement
construction.
As an example of SN determination, if a pavement is comprised of 6-in. of crushed stone
base (a2 = 0.14) and 4-in. of asphalt concrete (a, = 0.44), the pavement has a SN = 0.44*4
0.14*6 = 2.6.
DETERMINATION OF ESTIMATED PAVEMENT LIFE
Flexible Pavements
MSHTO Design Equation
The AASHTO Design equation for flexible pavements is:
logy = ZR*SO + 9.36*10910(SN + 1 ) - 0.20
(log'0(DPSI/2.7~/~0.40 + 1 094/(SN+1~5'9)
2 32 log'0MR - B.07
where:
Equation D1
We, = The predicted accumulated frame on the design lane during the design
period (typically 30 years) in equivalent ESALs,
SO =
SN =
MR =
the standard normal deviate corresponding to the desired design
reliability (for 50°/O reliability ZR = 0 and 1/2 of the pavement will fail before
the end of the design period, etc.) (a Apical reliability for major highways
is 95°/O with ZR = -1.64),
the overall standard deviation associated with pavement performance
prediction (a typical value for flexible pavements is 0.35),
the pavement structural number defined earlier,
the change in pavement serviceability during the design period (a typical
value is 1.9), and
the effective roadbed soil resilient modulus (AASHTO T 274) in psi.
Appendix G
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Example of Design Equation Use For purposes of demonstrating the effects of changes in
cumulative ESALs it may be best to simplify Equation D1 above by using typical values for all
variables except ESALs and SN. The 1993 AASHTO Design Guide offers a convenient example
where the following values are assigned:
ZR = -1.64 (reliability =
So=0.35
DPSI = 1.9
MR = 5000 psi.
Then, the AASHTO flexible design equation reduces to:
log,OW,~ = -0.26 ~ 9.36*10g,0(SN + 1 )
- 0.153/~0.40 + 1094/(SN+1~5'9)
Equation D2.
It should be emphasized that Equation D2 is a gross simplification of the AASHTO flexible
pavement design equation and should never be used for the design of specific pavements. The
sole purpose of the simplified equation is to permit analysis of the ESAL vs. thickness relationship
as a part of the study to assess the effects of weight enforcement on pavement performance.
To examine the effects of various cumulative ESALs on pavement life it is convenient to assume a
known existing pavement of say SN = 5. Equation D2 then solves
logy = 6.72 and W1B = 5.2 X 106.
If the traffic stream analyzed above for a flexible pavement with SN = 5 and p, = 2.5 IS used the
before (ESALt,) and after (ESALa) enforcement daily ESALs are 907 and 649, respectively.
It can be shown that a pavement undergoing an annual growth rate in frame volume will
accumulate the design We according to the equation
n = [log,0*~1 + r*V\/~!365*ESAL)l/log'0~1 + r)....Equation D3
where n = the estimated pavement life in years,
r = the annual growth rate expressed as a decimal,
ESAL = the average daily ESALs at the beginning of the analysis period.
Assuming a 5°/O annual rate of growth in traffic for the above example the pavement would have
been predicted to last
rib = [log,0*~1 + 0.05*5.2 x 106/365*9073/log'0~1.05) = 12.0 yrs.
With the same growth rate after enforcement the pavement would be predicted to last
na = [Iog,0*~1 + 0.05*5.2 x 106/365*6493/log'0~1.05) = 15.3 yrs.
Then, the increase in expected pavement life due to enforcement is 15.3 - 12.0 = 3.3 years or
27.5°/0.
Appendix G
6
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Rigid Pavements
AASHTO Design Equation
The AASHTO Design equation for rigid pavements is:
log, = ZR*SO + 7.35*1O91O(D ~ 1) - 0.06
[log'O(DPSI/3.0~/~1 + (1.624*107~/(D+1~846]
+ (4.22 - 0.32p')*1Og,o{[s'*c~(D°75
1 . 132~/~21 5.63*J(D° 75 - 18 42/(EJk)° 253) Equation D4
where, in addition to that defined above:
D =
Ec=
k =
the slab thickness (in.)
estimated mean PCC modulus of rupture (MSHTO T97) in psi,
a factor used to account for the ability of rigid slab to transfer loads
across discontinuities such as cracks and joints (typical values range
from 2.5 to 4.0, see AASHTO),
PCC elastic modulus in psi (typically 4 to 5 * 1 o6), and
the modulus of subgrade reaction, the load in pounds per square inch on
a loaded area of the roadbed soil or subbase divided by the deflection in
inches of the soil or subbase (psi/in), (typical values are 50 to 300~.
In addition, for rigid pavements the initial serviceability (PSIo or PSI at time 0) is about 4.2 while
the terminal or no longer acceptable serviceability (PSI~) is about 2.5. Therefore, a typical DPSI is
about 1.7.
Now, it is possible to solve Equation D4 for local conditions and, and making the appropriate
substitutions in Equation D3, go through the analysis of before and after enforcement traffic
streams to assess the impact of that enforcement on pavement life.
A more detailed discussion of the applied pavement-design analysis procedure by Consultant Ken
McGhee is contained in the NCHRP Project 20-34 documentation.
.7
Appendix G
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Calculate SN
If the user knows the material composition of the pavement, TWEET can automatically calculate
an SN value. In this case, the user clicks on 'Calculate SN', and the Automatic Calculation of SN
screen allows the user to select the appropriate surface, base, and subbase characteristics, i.e.,
pavement layer thickness (in inches), and strength coefficient. According to the specified material
type, the program will suggest the most appropriate default Strength Coefficient. Pavement
materials personnel who run this software have the option of overriding default values, depending
upon their own knowledge of pavement materials and design procedures along with specific
pavement characteristics associated with the enforcement location.
The structural number (SN) is a measure of relative pavement strength and is defined as:
SN = ash, ~ a2h2 + ~
where:
- - + ash' Equation D1
from the top down, hi is the thickness of layer one which has a layer coefficient of a,, h2
is the thickness of layer two which has a layer coefficient of a2, etc. Table D1 is a
tabulation of layer coefficients for materials typically used in flexible pavement
construction.
As an example of SN determination, if a pavement is comprised of 6-in. of crushed stone
base (a2 = 0.14) and 4-in. of asphalt concrete (a' = 0.44) the pavement has a SN = 0.44*4 +
0.14*6 = 2.6.
Select Truck Classification
This dialog allows you to select the type of truck classification system you wish to use. The
choices are FHWA 13-Type or Custom. The 1995 FHWA Traffic Monitoring Guide 13-Type
scheme is a standard 13-type vehicle classification system that should be adequate for most
users. NOTE: At the time this software was developed, many states applied the FHWA Card-
7format. If your data set is in the Card-7 format, go ahead and click on the default standard
13-type classification option.
If you wish to use a custom classification scheme, click on the Custom check box and press Next.
You will be prompted to enter the name for each of up to 15 different truck classifications in a
series of dialog boxes. If using this feature be sure to read the notes in the help screen (press
Help in the first Custom Classifications dialog).
File Conversion
This dialog box assists the user in converting data files to a an acceptable format. TWEET re-
quires all data files to be in either the 1995 FHWA Truck Weight Record format of Card 7. If your
data files are in one of these standard formats already, press Next to continue. If your data files are
in another format, press the Convert button below to run IWEETs conversion utility which will con-
vert your files to the proper format.
Appendix G
8
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TWEET Data File Conversion Utility
There are an abundance of truck weight data file formats in existence today. The TWEET analy-
sis tool supports the most common of these formats, the 1995 FHWA Truck Weight Record for-
mat. In an effort to assist users with data files formatted differently, TWEET incorporates a data
file conversion utility which will convert most custom file formats into the standard FHWA 1995
Truck Weight Record format, the format required by TWEET to measure enforcement effective-
ness. The conversion utility will also convert files of the popular Card 7 format into the 1995
FHWA Truck Weight Record Format.
Use of the conversion utility is fairly simple. For an overview of using the utility, click on Usinn the
Conversion Utilitv
For information on custom file formats, and how to enter them into the utility, click on Usinn Cus-
tom File Formats
Using the Conversion Utility
The TWEET Data File Conversion Utility main window provides a fast, efficient way to convert
data files from other formats to the 1995 FHWA Truck Weight Record format. Here is an overview
of the features of the main windows:
Input File field: This field allows the entry of the name of an input file (in some foreign format) to
be converted to the FHWA 1995 Truck Weight Record. If the name of the file is not known, the
Browse button allows for a file to be selected from the available files on the system's hard disk or
floppy disks.
Output File feld: This field allows the entry of the name of the output file to be created which will
contain the data in the input file, formatted in the FHWA 1995 Truck Weight Record format. If the
name of an already existing file is entered in this field, that file will be permanently overwritten.
Input Format field: This field allows for the selection of an input file format. There are Pro choices
of possible input file formats:
Card 7- Files of this popular format cannot be automatically converted to FHWA 1995
Truck Weight Record format files.
Custom - This option allows for the entry of a custom data file format, through the Cus-
tom Data Format dialog. For more information, see Usino Custom File Formats.
Output Format feld - This field, which is not changeable by the user, shows that all output files
processed by the TWEET Data File Conversion Utility will be formatted as FHWA 1995 Truck
Weight Record files.
Convert buffon - Once all of the four fields above have been set correctly (except for the Output
Format field, which is set by the program itself) pressing this button will
cause the file conversion to be performed.
9
Appendix G
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Advanced buffon - This button allows for the use of a custom file filter in the case that the regular
conversion program cannot handle a particular custom file format. A custom filter is a specific
routine written by a user that would plug in to the TWEET Conversion Utility to convert its own
unique, non-standard file format.
Help button - Brings up this help screen.
Exit button - Exits the TWEET Conversion Utility.
Using Custom File Formals
Pressing the Edit button in the main window or selecting custom from the Input Format field drop-
down list box will bring up the utility's custom data file format entry dialog. Here is an overview of
the options in this dialog:
Field Selection list box - The large list box at the left of the dialog allows for the selection of a par-
ticular field in the custom file format.
Columns Used For Highlighted Item fields - These fields correspond to the selected item in the
Field Selection list box. The Start field is the position in the file (the first character is considered to
be at position 1, the second at position 2, and so on) of the first character of the field; the End field
is the position in the file of the last character of the field. For example, if "Year of Data" is selected
in the list box, and the Start field reads "11" and the End field reads U14" it means that the 11th
through the 14th characters in the custom formatted data file contain the year of the data.
Checking the box labeled Field not present in custom formats means that the selected field does
not exist in the custom format, and it will thus be ignored. Some fields are required (e.g. axle
weights, etc.) and in these cases the U Field not present in custom format" check box is disabled.
Units Used In Custom Format fields - These fields allow for the selection of the type of units used
in the custom format. The Weight Units correspond to the type of units used in the gross vehicle
weight and axle weights. The Length Units correspond to the type of units used in the axle spac-
ings.
Select Data File Dialog
This dialog asks you to select a particular data file for the current condition. If you entered a "3" in
the previous dialog, indicating you wish to combine three data files for the study of the current condi-
tion, you will be presented with this dialog three times. Each time, select one of the three data files
you wish to use. For example, if the files were called DATA1.DAT,DATA2.DAT and DATA3.DAT,
you would select DATA1.DAT the first time, DATA2.DAT the second time, and DATA3.DAT the third.
Percentage of Overweight Trucks Dialog
This dialog displays the calculated percentages of overweight trucks in the sample. It lists four
calculations based on the data files:
A,opendi3< G
10
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Percentage of trucks over the legal gross weight limit This number is merely the percentage
of all trucks whose gross weigh exceeded the legal limit as set by the user in the Legal Weight
Limits dialog.
Percentage of trucks over the single axle weight limit This is the percentage of trucks ex-
ceeding the weight limit for a single axle.
Percentage of trucks over the tandem axle weight limit This is the percentage of trucks ex-
ceeding the weight limit for a set of tandem axles. Tandem axles are defined as a set axles which
are within a certain distance of each other, usually Oft (or metric equivalent). The sum of the
weights of each axle which is within this distance from the other axles is called the tandem axle
weight.
Percentage of trucks violating the Bridge Formula This is the percentage of all trucks in the
sample which violated the Bridge Gross Weight Formula. The presence of a violation is deter-
mined by using an equation, the Bridge Formula, which relates the axle spacing and axle weights.
Breakdown of Violations Dialogs
This is a set of two dialogs. The first dialog displays the breakdown of violations by day of week
and the second by the hour of the day.
Breakdown of Violations by Day~f-Week Dialog This dialog displays the percentage of viola-
tions occurring on each day of the week. The dialog simply lists each day of the week, and next
to it lists the percentage of all violations which occurred on that day. Note that only gross, single-
axle and tandem-axle violations are counted toward the percentages for each day (Bridge For-
mula Violations are not counted).
Breakdown of Violations by Day~f-Week Dialog This dialog displays the percentage of viola-
tions occurring at different hours of the day. Because it would be overly complex to display the
percentage of violations occurring at each of the 24 hours of the day, the five hours with the most
violations are list. If it is necessary to know what percentage of violations occurred at every hour
of the day, the Print option will be of use. The printed copy of the data, unlike the on-screen dis-
play, does display the percentage of violations for each hour of the day. Like the Breakdown of
Violations By Day of Week dialog, only gross, single-axle and tandem-axle violations are counted
toward the percentages for each hour.
Severity of Violations Dialog
This dialog displays the information about how severe the recorded violations were. The first part
of the dialog displays the absolute number of violations, once again divided into gross, single and
tandem violations. The second dialog displays the average number of pounds (or Metric equiva-
lent) overweight the trucks were. It too is divided into gross, single and tandem weights.
ESAL Data Dialog
This dialog displays the calculated average number of ESALs for each n-axled truck. ESALs are
the units in which pavement consumption is measured. Because the "normal" range of values can
11
Appendix G
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vary depending on how many axles a truck has, a different average ESAL value is given depend-
ing on the number of axles on the truck.
Truck Classification Data Dialog
This dialog displays the violation information as broken down by truck classification. This infor-
mation is useful in determining which types of trucks have the most (or least) violations, which
types of trucks are the most (or least) common on the road, etc. The dialog consists of two parts:
Truck Classification List Box This list box lists all of the truck classifications which were input
by the user during the beginning of the analysis, or if the default was selected, the FHWA 13-type
classifications. Click on one of these classifications with the mouse or select it with the arrow
keys on the keyboard. The data for the selected type of truck will appear at the right in the Viola-
tion Data section.
Violation Data This part of the dialog lists the violation data for the currently selected truck clas-
sification. The Total Number of Trucks field displays the number of trucks of the selected type
which were in the sample (regardless of whether they were violators). The Number of Violators
field lists the number of trucks of the selected type which violated the weight limits. The Percent-
age Violating field lists the percentage of trucks of the selected type which were violators (this is,
of course, simply the Number of Violators divided by the Total Number of Trucks).
Comparison of Enforcement Conditions Dialog
This dialog box contains results of applied significance tests to the computed M.O.E.s and indicates
to the user whether or not the observed differences are statistically significant. Separate tests of
significance were applied to M.O.E.s depending upon whether the measure was calculated as a
mean (i.e., average gross weight violation) or a proportion (i.e., proportion of gross weight violators).
Significance tests were applied at the .05 level of confidence.
Sampling Guide
This dialog box is an aid to determine how many sites will need to be surveyed in order to detect re-
gional changes for designated M.O.E.s given user-specified levels of certain statistical parameters
(which will be explained later).
The user is presented with a table indicating the number of sites which are required for data collec-
tion if specified levels of M.O.E.s changes (i.e., 5, 10, 15, or 20 percent) are to be detected. These
numbers are based on an iWEETs analysis of the measured statistical characteristics (e.g., vari-
ance) of the observed M.O.E.s. The user will note that fewer sites are necessary for larger differ-
ences. This effect is due to the fact that smaller differences in real-world truck weight enforcement
compliance are more subtle and therefore require more statistical rigor to detect.
Due to the fact that the number of required study site depends upon a variety of applied statistical
Appendix G
12
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criteria, the user is given the option of specifying two parameters related to the precision of the sta-
tistical estimate. These are the desired Level of Significance and the Power of Test.
Level of Significance refers, in this case, to the probability which the user is willing to risk the error of
rejecting a valid change in M.O.E. occurrence. In statistical jargon, the Level of Significance is the
maximum probability with which we would be willing risk a Type 1 error. A Type 1 error occurs when
a true hypothesis is rejected, i.e., that baseline versus enforcement M.O.E. variable sets are statisti-
cally different. In practice, a significance level of .05 or .01 is customary.
Power of Test refers to the likelihood of making a correct statistical assessment, Ike., that, statistically
speaking, the proper hypothesis is accepted. The issue is to what extent is the user willing to risk
accepting a invalid change in M.O.E. occurrence. In statistical jargon, the Power of a Test is the
maximum probability with which we would be willing risk a Type 2 error. A Type 2 error occurs when
a false hypothesis is accepted, i.e., that baseline versus enforcement M.O.E. variable sets are not
statistically different.
Under the Sampling Guide Options box within this dialog, the user has the option of varying the
Level of Significance and Power of Test. Required site sample numbers vary as function of these
statistical parameters.
Pavement Effects Analysis
This dialog box indicates the theoretical pavement design-life effect associated with differential en-
forcement-related ESAL loading conditions. Had the user opted to include the pavement design-life
effect computation, this screen would be displayed. Displayed information consists of the calculated
pavement ESAL capacity, the estimated pavement life under both observed enforcement conditions,
and estimated percentage pavement-life change due to the observed ESAL-loading difference assm
ciated with the enforcement activity. For information regarding computation of design pavement life,
see Me Pavement Analysis Dialon.
13
Appendix G
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Quick Start
This Quick Start topic is a comprehensive tutorial which will walk you through the step by step
process of conducting a sample truck weight enforcement analysis. If you have never used TWEET
before, this is a good place to start. As this Help screen comprises a number of pages, we suggest
that you make a printout for reference while running the program. Simply click on the UPrint' option
above.
Before performing this sample analysis, you may want to read the Overview topic to learn what
TWEET is and what it does.
Starting the Analysis
Start the TWEET program. From the main window, press the button marked "Start Analysis." This
will allow you to start a truck weight analysis and enforcement ejects.
First you will encounter a dialog labeled Select Units. Select the type of units you wish to use
(English or Metric) and press ~Next". See Select Units Dialon for more information.
Next, you will be asked to enter the weight limits you wish the program to use, via the Set Legal
Weight Limits dialog box. Default values have been set to the most commonly used weight limits.
If you need to modify these values, go ahead. Either way, press U Next" when you have finished.
See Lenal Weinht Limits Dialon for more information on this dialog.
Now the user will see the Select Truck Classif cation dialog box. This dialog allows you to select
the type of truck classification system you wish to use. The choices are FHWA 13-Type or
Custom. The 1995 FHWA Traffic Monitoring Guide 13
-Type scheme is a standard 13-type vehicle classification system that should be adequate for
most users. NOTE: At the time this software was developed, many states applied the FHWA
Card-7format. If your data is in the Card-7 format, go ahead and click on the default standard 13-
type classification option.
If you wish to use a custom classification scheme, click on the Custom check box and press Next.
You will be prompted to enter the name for each of up to 15 different truck classifications in a
series of dialog boxes. If using this feature be sure to read the notes in the help screen (press
Help in the first Custom Classifications dialog).
The File Conversion dialog box is designed to assist agencies whose data format does not
conform to either the 1995 FHWA Tragic Monitoring Guide 1 3-Type scheme or Card-7
classification formats. If your data is not in either one of these formats, press the Convert
button to run the conversion utility. For more information on using the Conversion Utility, see the
TWEET Data File Conversion Help screen.
Now the program is asking you to enter information about the enforcement conditions you are going
to study. Due to the fact that this exercise is just a demonstration of how to use the program, any
name, location, and set of dates will suffice. See the Enforcement Condition Dialog for more
information
The nrc~nram is will now ask vou about the data files you are going to use. These correspond to
enforcement conditions to be observed in the field. The Enforcement Condition 1 of 2 dialog box
appears. As a suggestion, why not enter the name Baseline" (as Enforcement Condition #1)
presenting a non-enforcement condition. This tutorial will provide you with such a data set.. It is not
necessary to enter a location and date to run the program. However, this information will be helpful
, _ _
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in the evaluation of actual truck weight enforcement operations. In this demonstration, enter
"Enforcement as Condition #2.
For each designated enforcement condition, a Number of Files for Condition dialog box asks for
the of WIM data files which pertain to each condition. For this exercise, designate one file for both
conditions One and Two. See Number of Files for Condition Dialoq for more information. Up to four
files can be utilized for each condition.
The program will now ask you to select (or name) the data files pertaining to each condition. You will
see a series of dialogs asking you to enter the path of each data file labeled "Select Data File x for
Enforcement Condition y" where x is the replaced by the number of the data file for which you are
currently selecting, and y is the number of the enforcement condition for which you are selecting data
files. For the purpose of this tutonal, select the "BASELINE.PRN" file for the first enforcement
condition and ENFORCE.PRN for the second condition. These files are located in the directory in
which you installed IWE ET. Please note that these are test data files representing an actual non-
enforcement versus an enforcement comparison. See Select Data File Dialon for more information.
The Pavement Analysis dialog box now appears. Here, TWEET gives the user the option of
conducting a pavement design-life enforcement-effects analysis. It will ask for specific (and detailed)
pavement design data. Because of the complexity of the pavement design-life analysis, the user has
the option of skipping the pavement analysis, i.e., simply click the 'skip pavement analysis' option.
More information on this process is provided in the Pavement Analysis Help screen.
Assuming that you want the pavement design-life analysis, first select the applicable pavement
material, either Flexible or Rigid. Note that depending on whether Flexible or Rigid pavement is
selected there will be a different set of variables in the Pavement Characteristics box at the bottom of
the dialog. This box will prompt the user for appropriate pavement design parameters.
Flexible pavement will be discussed first. Default values are shown on the screen for the following
parameters.
I
SN Pavement Structural Number. TWEET offers the option of computing this variable based on
input values provided by the user.
Initial Serviceability Index
pi
Terminal Serviceability Index
MR Default function of Serviceability Index
ZR
SO
Standard Normal Deviate corresponding to design reliability
Standard Deviation associated with pavement performance prediction
.
Because the pavement's Structural Number (SN) is so important, TWEET provides three ways for
the user to enter this value. First, he may accept the commonly-applied default value show here.
Second, he may apply his own value for SN, if it is known. Third, if the user knows the material
composition of the pavement, TWEET can automatically calculate the SN value. In this case, the
user clicks on 'Calculate SN', and the AutomaVc Calculation of SN dialog box allows the user to
select the appropriate surface, base, and sub-base characteristics, i.e., pavement layer thickness (in
inches), and strength coefficient. According to the specified material type, the program will suggest
the most appropriate default Strength Coefficient. Pavement materials personnel who run this
software have the option of overriding default values, depending upon their own knowledge of
15
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pavement materials and design procedures along with specific pavement characteristics associated
with the enforcement location.
In the event the user selects Rigid Pavement, the following design values are considered.
k
D
pi
Modulus of Subgrade Reaction
PCC Elastic Modulus
Slab Thickness (inches)
Standard deviation associated with pavement performance prediction
Initial Serviceability Index
Terminal Serviceability Index
As was the case with the Flexible Pavement Characteristics box, the most likely default values have
been provided. The user has the option of manually entering values specific to the highway study
site.
Viewing Results of Calculations
The program will now perform calculations. Unless your data files are extraordinarily large, these
calculations should take no more than a few seconds. If the data files are very large, or you are
using an older system, the calculations could take a while!
program's progress on the computational process.
A graphic will appear to advise of the
Once the calculations have finished, you will be presented with a series of Output" dialog boxes
which displays calculated values based on your input data. Press UNext " button when you are ready
to view the next calculation result.
You can press Help for more information about each dialog and its information, or click on one of the
following links:
Percentage of Overweight Trucks Dialon
Truck Classification Data Dialoq
Breakdown of Violations Dialogs
Severity of Violations Dialon
ESAL Data Dialoq
Data File Conversion Dialon
comparison of Enforcement Condition Dialon
Sampling Guide Dialon
Pavement Effects AnalYsis Dialon
The first M.O.E. dialog box, Seventy of Violations, also reports summary information, i.e., enforce
ment condition, highway type, total vehicle, and truck sample. The violator numbers and average
overweight values are indicated. Again, be reminded that displayed values, based on files BASE-
LINE.PRN and ENFORCE.PRN, contain data generated by an over calibrated Georgia LTPP sys-
tem; and therefore the numbers are unrealistically large.
The Calculated Percentages of Overweigh! Trucks dialog box provides percentages of trucks in
the sample which violate gross-, axle-, tandem-, tridem-, and Bridge Formula weight limits.
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The Violation Data by Truck Classification dialog box indicates violators, by truck number and
percentage, for each class of truck. Simply click on the truck classification list to the screen's left,
and the statistics appear of the right side of the screen.
The Breakdown by Day-of-Week and Hour-of-Day dialog boxes provide violations by day and
hour. However, day-of-week data were not coded for the sample data set and therefore results are
not provided. Time~f~ay violations are provided by indicating the five hours of the day (over the
entire sampling period) when the most violations occurred. The level of those violations for each
hour is shown. The sample data set contains only three hours of data.
The ESAL Data dialog box indicates average ESAL calculations using the FHWA Traffic Monitonng
Guide procedure according to the number of axles. This dialog also indicates computed Excess
ESAL violations by truck axlemount.
The next six dialog boxes contain the same M.O.E. calculations for Enforcement Condition #2.
Now, TWEET goes into its What does it all mean?' mode! The Companson of Enforcement Con-
ditions dialog box applies statistical significance tests to computed M.O.E.s and indicates to the
user whether or not the observed differences are significant. For more information, see the Com-
parison of Enforcement Conditions Dialon Help screen..
The Sampling Guide dialog box is an aid to determine how many sites will needed to be surveyed
in order to detect regional changes for designated M.O.E.s given specified levels of statistical con-
fidence. The Sampling Guide Help screen will assist in your understanding what the statistical terms
mean. It's not really that bad! This dialog box is based on an EWE ET' s analysis of the measured
statistical characteristics of the observed M.O.E.s. The user is presented with a table indicating the
number of sites which are required for data collection if specified levels of M.O.E.s changes are to be
detected. The user will note that fewer sites are necessary for larger differences. This is due to the
fact that smaller differences in real-world truck weight enforcement compliance are more subtle and
therefore require more statistical rigor to detect.
The final dialog box presents results of the Pavement Effects Analysis. This finding is based on a
theoretical pavement design-life effect, associated with differential enforcement-related ESAL loading
conditions. Had the user opted to include the pavement design-life effect computation, this screen
would be displayed. Displayed information consists of the calculated pavement ESAL capacity, the
estimated pavement life under both observed enforcement conditions, and estimated percentage
pavement-life change due to the observed ESAL-loading difference associated with the enforcement
activity.
Printing Out Results
Each out dialog box incorporates a Print button for the purpose of printing results shown. How-
ever, if you would like to print all of the results from your analysis rather than pressing the print
button in every single output dialog box, press the Print Results button once the main window ap-
pears. This window (which incorporates the Start Analysis button for a new data computation) will
appear following the output dialog boxes. The Print button in this dialog box will print all of the cal-
culated results from the last analysis for both enforcement conditions
. . . .. . ..
-
. . .
This concludes the Quick Start tutorial of the TWEET software. For more information, refer to any of
the links in this topic, or read the printed documentation.
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.
! ~ I.> r . `- . ? ..
Representative terms from entire chapter:
conversion utility
