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APPENDIX A PROGRAM OVERVIEW GENERAL DESCRIPI ION PAVDRN is a program package that was developed at The Pennsylvania State Un~versity's Pennsylvania Transportation Institute. The work was sponsored by the National Cooperative Highway Research Program Project I-29, "Improved Surface Drainage of Pavements." PAVDRN is intended for use by highway design engineers and determines the likelihood of hydroplaning on various highway pavement sections. It does this by computing the longest flow path length over a given pavement section and determining the water film thickness (depth of water above the roughness asperities of the pavement surface) at points along the path. The water film thickness is used to estimate the speed at which hv~ronIanin~ ,` ~, will occur. A worst-case scenario is examined by determining the water film thickness and hydroplaning speeds along the longest flow path length under steady-state conditions with a uniform rainfall rate. The predicted hydroplaning speed is compared to the design speed of the facility established by the engineer. Results are printed in a summary report format. A-1
INSTALLATION PAVDRN is distributed on two disks. The program runs under W~ndowsTM 3. fix or higher. (A FORTRAN version of the program is also available.) At a minimum, the computer used to run PAVDRN should have fiche following characteristics: · 80386SX or DX processor or above · MS-DOS 6.2 or above . WindowsTM 3. fix running ~ standard or enhanced mode or above The following steps describe the installation process: I. Insert distribution diskette ~ into a floppy disk drive. 2. From the W~ndowsw menu bar at the top of the screen, use the mouse and the left hand mouse button to click on File. 3. From the File pull-down menu, click on Run. 4. In the dialog box for Run, type a:setup or b: setup (depending upon which floppy drive you have Vertex distribution diskette ~ Anton. 5. Press Enter or click on OK. 6. Follow the directions shown on the Setup screens that follow. One of the first steps will be to provide the drive and subdirectory In which you want fiche program files installed. Certain files will also be copied to other subd~rectones like the \WINDOWS\SYSTEM subdirectory In addition to the files copied to the directory A-2
you indicated for the program files. Only the most current versions of files will be copied. This is intentional. The installation process creates a program group In the Program Manager window labeled PAVDRN. When the group is opened, three program icons are displayed. The one that most users will use routinely is ache PAVDRN program whose icon is a ram cloud. The PAVDRN program is started by double-clic~ng the left mouse button on this icon. The other two programs, SHARE.EXE and GSW.EXE, are only needed if a message appears on the user's screen prompting the user to start these programs. In most cases, they are not needed. USING PAVDRN After starting the PAVDRN program by double-clicking on the rain cloud icon labeled PAVDRN ~ the PAVDRN program group, the user should see the first of three screens that make up the user interface for the PAVDRN program. Screen ~ requires the user to input general ir formation about the simulation. Detailed information on each of the data items required for the first screen appears In the following. Screen 2 requires the user to input data concerning the specific section with which he or she is working or designing. The third screen is a screen used for displaying the data set constructed using Screens ~ and 2. It is also used to display the output from the PAVDRN program, which includes information about water film thickness and hydroplaning speeds along the length of the flow path. A-3
In general, the steps taken to use PAVDRN are: I. Open the PAVDRN program group. 2. Double-click on the PAVDRN rain cloud icon. 3. Edit the values and text on Screen ~ for the current pavement section or simulation. 4. Go to Screen 2. 5. Edit the values on Screen 2 for the current pavement section or simulation. 6. Return to Screen I. 7. Click on File on the menu bar at the top of the screen. 8. Click on Save on the drop down File menu and enter the name of the file In which you wish to save the data. (Another subdirectory can be selected at this point if desired). 9. Select Run PAVDRN from the File drop down menu or the Analysis drop~own menu on the menu bar at the top of the screen. 10. Select View PAVDRN results from the Analysis drop~own menu or the View drop~own menu on the menu at the top of the screen. . Print the output report or exit the viewing screen by clicking on one of the buttons at the bottom of the viewing screen. By using the View drop down menu, the output report or the data file can be examined neither file can be edited using this screen. The output file cannot be edited; the data file can be changed only by making changes to values In Screens ~ and/or 2. The output file and the data file are ASCH files and can be edited using a text editor such as the Notebook editor found In the Accessories group of W~ndowsTM. A4
SCREEN 1 - DATA INPUT AND EDITING The input data described in the following are required in Screen I, as displayed in figure Aft. They can be changed by using standard W~ndowsTM editing techniques or by using the spin or option buttons where provided. An example of an option button is the option for the Section Type, as described ~ the following. Spin buttons are used for the design speed and rainfall intensity on Screen 1. The tangent section is the only section that accommodates different texture depths, cross-sIopes, and pavement types within a single section. All other sections have only one value for each of these variables in the PAVDRN model. Note that Screen ~ is Initiated with default values that should be edited for the specific pavement section berg analyzed. Also, Screen ~ is the only screen that coffins the menu bar at the top of the screen. Section Description This part of the screen allows the user to provide a description of the design sections. Three lines, 72 characters each, are used to describe the section and any other unique aspects of the simulation. A-S
Eric View Analysis Help Data Input - Semen ~S=tion Description Enter dest:'ipt've information for this analysis here [Use up to three lines to describe of label the analysis of this Motion} ~Sect'.n Type 0 Tangent O Transition O Vertical West O Vertical Sag ~Rainfall Intensity, ~ Design S peed @~ ~Water Temperature ~Kmematic Viscosity- ~ @ ~ . _ ~System of llnits~ BUS O libretti': {SI} n use data from upstream pavement section _ Figure Apt. Example of PAVDRN input screen 1, environment and section type. A-6
Section Type Five different design sections are considered (see figure A-2 for the plan and profile views of each type of section). Tangent Section. A tangent section is a straight section that may consist of up to ten planes (sections with varying sloped that have unique cross-slopes, widths, texture depths, and/or pavement types. HonzontaZ Curve Section. A horizontal curve section contains a circular curve with both the grade and superelevation specified. Transition Section. A transition section is a straight section with a grade In which the cross-sIope at the tangent end changes to meet the superelevation of the curved section. Crest Vertical Curve Section. A vertical curve section is a section with a cross-slope that crests between point of curvature (PC) and point of tangency (PT). Sag Verucal Curve Section. A sag vertical curve section contair s a cross-slope that sags between the PC and the PT. A-7
A A MA Plan Pmfi~e al Tangent Simian ALA Or 1] MA Plan Profile Transition Se~ion J A / I/? AM Plan Profile by HoNzonte' Cur Simon A AM - Plan Profile and c] Crest and Sag Verbal Cu~s Figure A-2. Pavement cross sections included In PAVDRN. A-8
System of Units The system of units used for input and output (ST or English) may be chosen at the option of the user. RamfaU Intensity The rainfall intensity must be selected by the user In units of in/in or mm/in. The selection of a value for the rainfall Intensity is discussed In the following. Water Temperature The temperature of water flowing over the pavement surface must be selected by the user In mats of °F or °C. Kinematic Viscosity of Water The kinematic viscosity used In this simulation is expressed ~ units of ft2/s, m2/s. The value for the kinematic viscosity is calculated by an aIgori~chm within PAVDRN as a function of the water temperature. The lowest possible water temperature should be used, keeping iIr mind the ra~nfaD Utensil and the season of the year. The temperature of the water may be A-9
different than the ambient air temperature depending on pavement temperature and rainfall duration. Design Speed The design speed for the pavement section being analyzed must be specified by the user In either mi/h or km/in. Multiple (Joined) Sections If the simulation is set up for a pavement section that is downstream from a previously analyzed section, and if the program output for the previously analyzed section indicates that the flow path extended to the end of the section, click on the box. This option allows the conditions existing at the end of ache previous section to be linked to the new section. A typical screen for a Portland cement concrete pavement and a porous asphalt pavement are shown In figures A-3 and Am. A-IO
Data Input - Screen 2 Tangent Section ~Numbe' of Planes _ _ 1 ~ ~Scct'an Lcngth 110110 ~ r pavement Grader 1-01 1 ~Step S=e ~ Plane Properties _ Plane 1 ~Plane W;dth 112 1 Pavement Type O DG^C ~ PCC Q OGAC O G-PCt: F[:'oss~ope 1 |.015 ~ rTcxhre Depth l I Q2 1 Figure A-3. Example of PAVDRN input screen 2, geometric requirements for Portland cement concrete pavement. A-11
Data Input - Screen 2 Tangent Se':tion -Number of Planes if I - .. ~Set:tu~n Length 1looo ~ , P- ~ avement Brat e ~ , Colt 1 , instep Size - Plane Properties |Pians 1 -lilt-AC Permeability 10 1 p Plane W'dth l E:T ~Pavement Type DO-AC O PCI: OG-AC O G-Pl:1: ~ Ctoss-slope Cola 1 rapture Depth l [.02 ~ 1 Figure Am. Example of PAVDRN input screen 3, geometric requirements for porous asphalt. A-12
SCREEN 2 - DATA INPI~ AND EDITING Each of the different types of sections (selected from Screen 1) has a unique Screen 2 because of the different types of information required for each section type. The data required for each of these screens are described In the following according to the type of section. Tangent Section Number of planes. This section is used to define the number of planes sloped In one direction that form a series of planes over which flow will cascade until it reaches the edge or end of the pavement. This feature allows the user to simulate the effect of using different pavement materials and cross-sIopes In different lanes of pavement. Up to ten different planes can be included. Section Length. This entry defines Me length of pavement section in the direction of travel (ft. m). Pavement grade. This entry defines the longitudinal slope or grade of the pavement In the direction of travel (ft/ft, m/m). Step Size. The computational step size (ft. m) determines the points along the flow Pam at which the water film thickness and hydroplaning speeds are computed. These values are reported In me suitor ary tables of the output. A-13
Plane Properties. For each plane, the pavement type, cross-slope, mean texture depth, and plane width are required. First, use ache drop down list showing the plane number for which input data will be edited, and click on the appropriate plane number in the drop down list. Pavement Type Four types of pavements are used in PAVDRN; they are: · PCC: Portland cement concrete, · GPCC: Grooved Portland cement concrete, · DGAC: Dense-graded asphaltic concrete, and · OGAC: Open-graded or porous asphaltic concrete. When grooved PCC is selected as the pavement type, text boxes for the groove spacing, the groove width, and ache groove depth are displayed. This information is used to effectively increase the mean texture depth of the pavement. If open-graded or porous asphaltic concrete is selected as the pavement type, an additional text box is displayed to provide a place for entering a value for the permeability of the pavement (mm/~? in/h). This value is used to reduce ache amount of water available for surface Canon. The value for pavement permeability is set to zero for all other pavement types. A-14
In general, porous pavements, if they and their bases are designed and constructed correctly and not clogged, will remove all runoff water from the surface. Isenring et al. (13) found permeabilities that ranged from 0.75 to 3.5 mm/s. This rate far exceeds a maximum design rainfall rate for surface runoff of 150 mm/in. The OGAC permeability then should be the "effective" permeability of the pavement. Cross-siope. This entry defines the cross-slope of the pavement surface (ft/ft, mlm). Texture Depth. The texture depth is the mean texture depth using a standard sand patch test (ASTM E 965) or equivalent fin, mm). The following are typical values for the mean texture depth and may be used if texture depth or sand patch measurements are not available. · PCC 0.25 - 1.! mm 0.01 - 0.044 in · DGAC 0.23-~.Omm 0.009-0.065~n · OGAC 1.0 - 4.1 mm 0.04 - 0.161 In Plane With. This entry defines the width of the pavement section (ft. m). Horizontal Cure Section Section Grade. A longitudinal slope or grade in the direction of travel along the center line of the pavement is defined in this entry (ft/ft, m/m). A-15
Superelevation. In this entry, the superelevation or cross-slope of the curve (ft/ft, m/m) is defined. The values are always positive. Radius. In this entry the radius of curvature (ft. m) is defined. Pavement Faith. This entry defines the width of ache curved pavement section (ft. m). Pavement Type. There are four types of pavements are used in PAVDRN; they are: · PCC: Portland cement concrete, · GPCC: Grooved Portland cement concrete, · DGAC: Dense-graded asphaltic concrete, and · OGAC: Open-graded or porous asphaltic concrete. When grooved PCC is selected as He pavement type, text boxes for the groove spacing, the groove width and the groove depth are displayed. This information is used to effectively increase the mean texture depth of ache pavement. If open-graded or porous asphaltic concrete is selected as the pavement type, an additional text appears to provide a place for entering a value for the permeability of the pavement. This value is used to reduce the amount of water available for surface runoff. The value for pavement permeability is set to zero for all other pavement types. A-16
Texture Depth. The mean texture depth is selected In this entry. The value used may be based on using a standard sand patch test or a profile measurement fin, mm). Step Size. The computational step size (ft. m) determines the points along the flow path at which the water film thickness and hydroplaning speeds are computed. These values are reported In the summary tables of the output. Transition Section Three categories of data are required for the transition section In PAVDRN: data for the tangent section end, data for the curved section end, and data for the transition section itself. Tangent End of Transition Section Infolmation provided about He tangent end of the transition section include values for grade, runout length, cross-slope, and pavement width. Gratle. This is the longitudinal slope or grade of the transition section in the direction of travel (ft/ft, mJm). Runout Length. This is the length of the transition section in the direction of travel (ft. m). A-17
Pavement Width. This is the width of the transition section pavement at the tangent end of the transition (ft. m). . . Cross-siope. This is the cross-sIope of the transition section pavement at the tangent end of the transition (ft/ft, mJm). The cross-sIope value can be positive or negative (adverse to the superelevation of the curve end of the transition). Curve End of Transition' Section Information provided about the curve end of the transition section mclude values for pavement width and superelevation. Pavement Huh. This is the width of the transition section pavement at the curve end of the transition (ft. m). SupereleYation. Superelevation or cross-sIope of the curve at the curve end of the transition section (stiff, m/m). The value is always positive. General Data for Transition Section Three items, pavement type, texture depth, and step size apply to the entire transition section. A-~S
Pavement Type. Four types of pavements are used in PAVDRN; Hey are: · PCC: Pordand cement concrete, · GPCC: Grooved Portland cement concrete, · DGAC: Dense-graded asphaltic concrete, and · OGAC: Open-graded or porous asphaltic concrete. When grooved PCC is selected as the pavement type, text boxes for the groove spacing, the groove width and the groove depth are displayed. This information is used to effectively increase the mean texture depth of the pavement. If open-graded or porous asphaltic concrete is selected as the pavement type, an additional text box appears to provide a place to enter a value for the permeability of the pavement. This value is used to reduce the amount of water available for surface runoff. The value for pavement permeability is set to zero for aD other pavement types. Texture Depth. Mean texture depth using a standard sand patch test or equivalent fin, mm). Step Size. Computational step size (ft. m). This value determines the points along the flow path at which the water film thickness and hydroplaning speeds are computed. These values are reported In the summary tables of the output. A-19
Crest Vertical Curve Section Length of Vertical Curve. Hornont~ length of the vertical curve (ft,m). Pavement Edith. Width of the pavement (all lanes sloping In one direction toward the edge of the pavement) (ft. m). Cross-siope. Cross-siope of the pavement (ft/ft, m/m). The cross-slope value is always positive. Grade at PT. Longitudinal grade or slope at the point of tangency (PT) (ft/ft, mlm). The grade is negative if elevations decrease from left to right. Grade at PC. Longitudinal grade or slope at the point of curvature (PC) (ft/ft, m/m). The grade is positive if elevations increase from left to right. Relative Elevation. Relative elevation of Me PT to the PC (ft. m). The relative elevation is negative if Me PT is lower than the PC. Texture Depth. Mean texture depth using a standard sand patch test or equivalent (in, mm). A-20
Step Size. Computational step size (ft. m). This value determines the pouts along the flow path at which the water firm thickness and hydroplaning speeds are computed. These values are reported in the summary tables of the output. Pavement Type. Four types of pavements are used In PAVDRN; they are: · PCC: Portland cement concrete, · GPCC: Grooved Portland cement concrete, · DGAC: Dense-graded asphaltic concrete, and · OGAC: Open-graded or porous asphaltic concrete. When grooved PCC is selected as the pavement type, text boxes for the groove spacing, the groove width and the groove depth are displayed. This Information is used to effectively increase the mean texture depth of the pavement. If open-graded or porous asphaltic concrete is selected as the pavement type, an additional text box is displayed to provide a place for entering a value for the permeability of the pavement. This value is used to reduce the amount of water available for surface runoff. The value for the pavement permeability is set to zero for all other pavement types. Direction of Flow from the Crest. This item requires that the user determine for which side of the crest vertical curve PAVDRN will calculate the water film chic Hess aunt hydroplaning speeds. In some cases (i.e., where the Err or the PC is the crest pointy only one selection makes sense. A-21
Sag Vertical Curve Length of Vertical Curve. Horizontal length of the vertical curve (ft,m). Pavement Moth. Width of the pavement (all lanes sloping in one direction toward the edge of the pavement) (ft. m). Cross-siope. Cross-sIope of the pavement (ft/ft, m/m). The cross-slope value is always positive. Grade at PT. Longitudinal grade or slope at the point of tangency (PI) (ft/ft, mlm). The grade value is negative if elevations decrease from left to right. Grade at PC. Longitudinal grade or slope at the point of curvature (PC) (ft/ft, m/m). The grade value is positive if elevations Increase from left to right. Relive Elevation. Relative elevation of the PT to the PC (ft. m). The relative elevation is negative if the Pr is lower than the PC. Texture Depth. Mean texture depth using a standard sand patch test or equivalent fin, mm). A-22
Step Size. Computational step size (ft. m). This value determines the points along the flow path at which the water fihn thickness and hydroplaning speeds are computed. These values are reported In the summary tables of ache output. Pavement Type. Four types of pavements are used in PAVDRN; they are: · PCC: Portland cement concrete, · GPCC: Grooved Portland cement concrete, · DGAC: Dense-graded asphaltic concrete, and · OGAC: Open-graded or porous asphaltic concrete. When grooved PCC is selected as the pavement type, text boxes for the groove spacing, the groove width and the groove depth appear. This information is used to effectively Increase the mean texture depth of the pavement. If open-graded or porous asphaltic concrete is selected as the pavement type, an additional text box is displayed to provide a place to enter a value for He permeability of the pavement. This value is used to reduce the amount of water available for surface runoff. The value for pavement permeability is set to zero for all other pavement types. Direction of F70w to the Sag. This item requires that the user determine for which side of Be sag vertical curve PAVDRN will calculate water film thickness and hydroplaT ing A-23
speeds. In some cases (i.e., where the PT or the PC is the sag point) only one selection is meaningful. PAVDRN RESULTS AS AN EXAMPLE PAVDRN produces a summary report as the result of its execution. The report can be viewed on-screen by selecting View or Analysis from the menu bar on Screen 1. The report can also be printed and has two parts. The first part presents an "echo" print of the data provided by the user. It should be examined to ensure that correct values were used In the simulation of runoff over the pavement section. Table A-1 is an example of the data set produced by PAVDRN for a tangent section. Table A-2 shows part ~ of fiche report produced by PAVDRN. TEST DATA SET - USERS GUIDE Table Apt. PAVDRN input data set. Tangent Section - 4 lane pavement with variable cross-slope PCC Pavement 1,1,2,.00001134,55,0 2,1000,.01,3 24,.015,1,0,.02 24,.02,1,0,.02 A-24
Table A-2. PAVDRN output - Part I: Echo print of input data. PAVDRN - Highway Drainage Program - Version 1.O developed by R. S. Huebuer (717)948-6127 Pennsylvania Transportation Institute The Pennsylvania State University University Park, PA 16802 Sponsored by the National Cooperative Highway Research Program NCHRP Project 1-29 Program started on 5/ 1/1997 at 22:55:59 TEST DATA SET - USERS GUIDE Tangent Section - 4 lone pavement with variable cross-slope PCC Pavement Type of section System of units for input and output Number of consecutive planes Rainfall intensity (in/h, mm/in) Kinematic viscosity (sq.ft./s, sq.m.is) Section length (ft. m) Longitudinal slope or grade (ft/ft, m/m) Section design speed (mi/h, km/in) Computational step size (ft. m) Tangent US 2 2.00 .llE-04 1000.00 .lOE-O1 55. 3.00 Plane No. Length Slope Pavement Infiltration Texture (ft. m) (ftIft, m/m) Type Rate(in/h,mm/h) Depth (in, mm) 1 24.0 .015 PCC .000 .020 2 24.0 .020 PCC .000 .020 A-25
The second part shows the results of the analysis In tabular form, table A-3. Table A-3. Example of a PAVDRN analysis results screen. Results for Plane No. 1 X Y Distance AFT Flow/width Manning's n Reynold's No. Hydr. Speed (ft,m) (ft,m) (ft,m) (in,mm)(cfs/ft,cms/m)(mi/h,km/h) .0.0.00- .20E-O1 . OOE+OO .000 0. 999999 2.03.03.61.21E-01 .17E-03 .092 15. 71 4.06.07.21.29E-01 .33E-03 .064 29. 65 6.09.010.82.35E-01 .50E-03 .051 44. 62 8.012.014.42.40E-01 .67E-03 .044 S9. 60 10.015.018.03.44E-01 .83E-03 .039 74. 59 12.018.021.63.47E-O1 . lOE-02 .035 88. 57 14.021.025.24.50E-01 .12E-02 .032 103. 57 16.024.028.84.53E-01 .13E-02 .030 118. 56 Notes: 1) + denotes Reynold's numbers greater than 1000. (Manning's n may be in error) 2) * denotes hydroplaning speeds less then the facility design speed of 55. (mi/h, km/in) 3) Hydroplaning speed is equal to 999999. for water film thickness less than or equal to O.O Time to equilibrium for place 1 is 2.19 min. Total time to equilibrium at the end of this plane is A-26 2.39 min.
Table A-3. (Continued) Results for Plane No. 2 X Y Distance WIT Flow/width Manning's n Reynold's No. Hydr. Speed (ft,m) (ft,m) (ft,m) (in,mm)(cfs/ft,cms/m) (mi/h,km/h) 16.0 24.0 28.84 .48E-01 .13E-02 .030 118. 57 17.5 27.0 32.20 . SOE-01 .15E-02 .029 131. ~ 6 19.0 30.0 35.55 .52E-01 .16E-02 .027 145. 56 20. ~33.0 38.91 .54E-01 .18E-02 .026 159. 55 22.0 36.0 42.26 .56E-01 .20E-02 .025 173. 55 23.5 39.0 45.61 .58E-01 .21E-02 .024 186. 55 25.0 42.0 48.97 .59E-01 .23E-02 .023 200. 54* 26.5 45.0 52.32 .61E-01 .24E-02 .022 214. 54* 28.0 48.0 55.68 .62E-01 .26E-02 .021 227. 53* Notes: 1) + denotes Reynold's numbers greater than 1000. (Manning's n may be in error) 2) * denotes hydroplaning speeds less than the facility design speed of 55. (m'/h, km/in) 3) Hydroplaning speed is equal to 999999. for water film thickness less than or equal to O.O Time to equilibrium for plane 2 is 2.46 min. Total time to equilibrium at the end of this plane is 4.65 min. Program completed successfully at 22:55:59 The table contains X and Y coordinates for the flow path length, as well as the length of the flow path. X and Y are zero at the beginning of the flow path. This location varies with different pavement section types as described in the following section. The water film thickness above the pavement roughness asperities and the flow-per-unit width of the plane along the flow path are also displayed. The far right column shows the predicted hydroplaning speed. (The basis for this value is described in the following). Manning's n and Reynold's A-27
number at each point are also presented. A number of notes that pertain to the results conclude the output report. An estimate of the tune of concentration for the pavement section is also reported. This value is useful in selecting an appropriate rainfall intensity for the analysis. A comma~elimited, ASCH text file with the extensionplename.ASC contains Me data shown ~ table Ant. These data can be incorporated into a ~ird-par~ plotting package to aid In the interpretation of the results. The origin of the flow Dath can be identified as follows: Tangent Section The origin can be located anywhere along the upper edge of the pavement section (i.e., the inside edge of the first plane). Horizontal Curve Section The origin is difficult to identify, however, the terminal point of the flow path is the lowest point ~ the curve. Assnmmg a grade and superelevation, this would be at the corner of the inside edge of the lower part of the curve. If the curve has no grade, the origin can be located at any point along the upper or outside edge of the curve. The flow should be directly across the pavement to the inside edge. A-28
Transition Section If He tangent end of the transition and the curve end of the transition have slopes In the same direction, the origin is located up from the end with the mildest slope and along the upper edge of the pavement. If the tangent end and the curve end of the transition section have adverse slopes, the origin is located at the point of zero cross-slope along the length of the section. This point should be accurately located by the x-coord~nate shown In ache printout. The flow path extends from this point toward the end of the section with the mildest cross-sIope. This is not necessarily the end with the smallest slope but, rather, the end where the change ~ cross-sIope per unit per length is the smallest. Crest Vertical Curve Section The outlet of the flow path is located at the lower edge of the pavement section at the PC or Pr, depending upon which side of the vertical curve is being analyzed. The origin is located up-gradient from the outlet point. The x-coordinate of the origin is located using the value shown in the printout. The flow path extends from this point toward the end of the section with the mildest cross-sIope. It is not necessarily the end with the smallest slope but, rather, the end where the change in cross-slope per unit length is the smallest. A-29
Crest Vertical Curve Section The outlet of the flow path is located at He lower edge of the pavement section at the PC or PI, depending upon which side of the vertical curve is being analyzed. The origin is located up-gradient from the outlet point. The x-coordinate of the origin is located using the value shown ~ the printout. Sag Vertical Curve Section The outlet of the flow path is located at the lower edge of the pavement section, i.e., the sag, where the longitudinal slope is zero. The origin is located up-gradient from this outlet point. The x-coordinate of the origin is located using the value shown in the printout. BASIS OF CALCllLATION The basis for the value computed for the predicted hydroplaning speed is described in detail in an article by Huebuer, Reed, and Henry (38). The algorithm uses two expressions for computing the hydroplaning speed. The first is based on data collected by Agrawal and Henry (44J and is based on a regression expression of their data (water film thickness versus hydroplaning speed) to predict the hydroplaning speeds for water film thicknesses less than 2.4 mm (0.095 in). The second is used for water film thicknesses greater than 2.4 mm (0.095 in) and is based on an expression developed by Gallaway et al. (4), where the hydroplaning speed A-30
is a function of water film thickness, tire tread depth, pavement mean texture depth, and tire pressure. Conservative values of the tire pressure, 165 kPa (24 lb/in2), and tire tread depth, 2.4 mm (3/32 Ins, were used in the PAVDRN model to generalize Gallaway's expression. One method for the selecting the design rainfall intensity for the hydroplaning analysis is based on the frequency and duration of an event. It is recommended that a frequency of 100 years (100-year return period) be used representing a one-percent risk or chance, so the Intensity will be exceeded. The duration should be based upon the pavement's time of concentration. The time of concentration can be determined using output from the PAVDRN model. In summary, the key parameters for selecting a value of rainfall intensity based on hydrologic considerations in order to estimate the hydroplariing potential of a pavement surface are: (1) location, (2) risk level, and (3) time of concentration. A second method of selecting a rainfall intensity for hydroplaning analysis is by examining the effect of driver response. Table AN was developed based upon work done by Hayers et al. (45) and AASHTO. Clearly, the selection of the design rainfall intensity for analyzing He hydroplaning potential of a highway section needs to consider both driver response and the likelihood of an event or risk. It is recommended that the designer employ a value from table AN to establish a maximum rainfall intensity specifically for determining the potential for hydroplaning on the designed pavement section. The value should be compared with the rainfall information 0-D-F A-31
curves) for the location of the project. The user should select the lesser of the two values and use it for completing the hydroplaning analysis of the pavement section. Table A4. Rainfall intensity for stopping sight distances. Design Speed Stopping Sight Maximum Rainfall Intensity, m/in, (kmlh) Distance, It (m) in/in, (mm/h) . 50 (80) 55 (88) 60 (96) 65 (104) 70 (112) 475 (145) 550 (167) 650 (198) 725 (221) 850 (259) 5.96 (151) 4.18 (186) 2.88 (73) 2.18 (55) 1.54 (39) A-32
