Bentley Civil Guide. SELECT series 3. Setting Up Superelevation SEP Files. Written By: Lou Barrett, BSW-Development, Civil Design

Transcription

1 Bentley Civil Guide SELECT series 3 Setting Up Superelevation SEP Files Written By: Lou Barrett, BSW-Development, Civil Design Bentley Systems, Incorporated 685 Stockton Drive Exton, PA

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3 Table of Contents Preface... 1 Superelevation Preferences (SEP) File... 3 Overview... 3 General Reference... 3 Editing the Superelevation Preferences (SEP) File... 3 Editing CSV Files... 3 Terminology... 4 Percentages... 4 e... 4 Normalized Grade Diagrams... 4 Relative Gradient... 4 Runoff, Tangent Runout, and Total Transition Lengths... 5 Normal Crown, Reverse Crown and Maximum Cross Slope... 5 Interpolation... 5 Rounding... 6 Calculation Overview... 7 E Computation... 8 AASHTO Method Radius Table... 9 Assumptions Specific to Radius Table csv Files... 9 Equation 10 Runoff Length Spiral Circular Curve (Unadjusted Length Computation) e Table Relative Gradient Table Equation Tangent Runout Tangent Runout Distance From Relative Gradient Tangent Runout Distance - Fixed Distance Tangent Runout Distance - Equation Guide: Setting Up Superelevation SEP Files i

4 Table of Contents Adjustment Factors Distribution 17 Base Adjust Factor On: Option Multilane Runoff Length Adjust Factors Undivided vs. Divided Roadway Distribute Over % on Tangent Divided Roadway (Low Side) Station Rounding Rotation Transition Profile Transition by Slope Transition by Elevation Example Outside Lane Rotation Axis of Rotation Superelevation Transition Conflict Resolution Overview 22 Methods of Distributing Modifications Multiple Conflicts Spirals 23 Reverse Curves Critical Case Supercritical Case Treatment % Positioning Relative Gradient Compound and Broken Back Curves Compound Curves Determine Transition Length Length Distribution at PCC Broken Back Curves Maintain Minimum Normal Crown Length Maintain Minimum Reverse Crown Length Short Curves ii Guide: Setting Up Superelevation SEP Files

5 Table of Contents Appendix A: Summary of Preferences Options Overview 34 E Runoff Length Tangent Runout Adjustment Factors Distribution Rotation 37 Reverse Curves Critical Case (Maintain Normal Crown Section) Supercritical Case (Remove Normal Crown Section) Compound Curves Broken Back Curves Short Curves Guide: Setting Up Superelevation SEP Files iii

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7 Preface This guide is equally applicable for the MX, InRoads or GEOPAK families of products. Each product contains the identical toolset and identical workflow. Note Prerequisite Knowledge Level: Participant should have a basic understanding of road design principles <any specialty requirements> and be fluent in the use of one of the Bentley Power products or CAD and the native application (MX, InRoads or GEOPAK). Guide: Setting Up Superelevation SEP Files 1

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9 Superelevation Preferences (SEP) File OVERVIEW A rich set of preferences is available which gives the administrator / user complete control over every aspect of the standardization of the superelevation design process. AASHTO Method 5 is available as a default, along with the ability to employ user-defined lookup tables both for e (superelevation rate) and for runoff length. User-defined equations may also be entered to compute these values. A thorough set of options is available for resolving the superelevation conflicts of Reverse Curves, Compound Curves, Broken Back Curves, and Short Curves. Hence, the categories of preferences are: GENERAL REFERENCE E Calculation Runoff Length Tangent Runout Adjustment Factors Distribution Rotation Superelevation Transition Conflict Resolution o Reverse Curves o Compound and Broken Back Curves o Short Curves EDITING THE SUPERELEVATION PREFERENCES (SEP) FILE When editing a Preferences file with a text editor, comments may be inserted. Comments are delineated with a dollar sign ('$'). Comments may take up an entire line, or may be on the same line as a data entry. When a $ is found on a line, Bentley Civil does not read that line any further. The lines can be any order within the file. In the sample, they are in the same general order as the groupings in this document. EDITING CSV FILES There are a few assumptions which Bentley Civil makes about all types of tables. The first assumption is that when there is a line with a name in brackets, such as [Urban] in the example, that line marks the beginning of a new table, which is referred to in the Calculation Dialog by that name. The second assumption is that the first row following the name row must be populated with Design Speeds. The first cell of that second row should be blank, and the Design Speeds serve as column headings for subsequent rows. The final generalized assumption regarding CSV tables is that Design Speeds increase as one reads from left to right. There are other assumptions made by the software about the layout and design of the various tables. Those assumptions, being specific to the individual table types, are explained in the appropriate Guide: Setting Up Superelevation SEP Files 3

10 Terminology sections and examples are given. Failure to abide by these assumptions in laying out the csv files will likely cause unintended results. TERMINOLOGY While the terminology is industry standards, it is prudent to review to ensure your organization s nomenclature is consistent or where adjustments need to be made. PERCENTAGES In both the documentation and the calculation application, cross slope values are given to and expected from the user as percentage values. Therefore, if a superelevated section of roadway had a cross slope of 0.06 ft/ft, the value would be reported as 6%. E Throughout this documentation and the application, the symbol "e" is used to represent superelevated cross slope. NORMALIZED GRADE DIAGRAMS Several of the diagrams in Bentley Civil Superelevation utilize the concept of a Normalized Grade. Also referred to as "Diagrammatic Profiles," Normalized Grade Diagrams are plots of key points on a roadway in profile view as if the roadway grade were flat, zero percent. They are also known as superelevation diagrams. RELATIVE GRADIENT Relative Gradient refers to the rate of change of elevation of a control point (such as an edge of pavement) relative to the grade point (or some other control point). As depicted on the Normalized Grade Diagram below, Relative Gradient is defined as the change in elevation over the length of transition. Relative Gradient is related to Slope Factor in Bentley Civil Superelevation. A Slope Factor of 1:200 is equivalent to a Relative Gradient of Guide: Setting Up Superelevation SEP Files

11 Terminology RUNOFF, TANGENT RUNOUT, AND TOTAL TRANSITION LENGTHS The following Normalized Grade Diagram illustrates the terms Runoff Length, Tangent Runout Length, and Total Transition Length as they are used by the software and in this documentation. NORMAL CROWN, REVERSE CROWN AND MAXIMUM CROSS SLOPE Some Roadway Typical Cross Sections (abbreviated to Typical Sections) will have what may be termed as "Broken-Back Slopes." Broken Back Slopes are when parts of the Typical Section have differing cross slopes while in a non-superelevated state. This is illustrated in the following Typical Cross Section Diagram. Normal Crown is defined as the cross slope of the lane closest to the profile grade point. In a case such as the one depicted above, Normal Crown is -2% and the Maximum Cross Slope is -3%. The reason this distinction is important is for situations when the Tangent Runout Length is set to a fixed distance. A decision must be made as to whether that specified length applies to -2% or -3%, still referring to the above Typical Section. When the approach to computing the superelevation transition stations in such a situation as this is documented in the log file, it is essential to understand how these terms are being used. Further when the Typical Section is similar to the one depicted above, the question arises as to what the term Reverse Crown means. In Bentley Civil Superelevation, Reverse Crown means negative one times Normal Crown. Therefore, the cross section of a curve in Reverse Crown, being based on the above Typical Section, would be as follows: INTERPOLATION For the various tables, it often happens that values which are not found in the given table must be handled. How Bentley Civil handles this kind of situation is determined by several options labeled "Interpolation" in the Superelevation preferences dialog. Guide: Setting Up Superelevation SEP Files 5

12 Terminology ROUNDING Radius interpolation applies only to Radius Table for e computation. e interpolation applies only to e Table for length computation. Every Interpolation option allows one of the three following: Linear, Closest Entry, or Conservative Entry. Linear Interpolation causes Bentley Civil to perform a straight-line interpolation between the two possible values. Closest Entry forces the computed value to equal a value found in the table. The selected value is determined by how close the indexed number is to either of the two choices. For example, if radius equals 1150, but the closest values available in the table are 1200 and 1000, e would be computed based on the 1200 radius row because 1150 is closer to 1200 than it is to Conservative Entry forces the computed value to equal the more conservative of the index values. For radius, it causes the value to be adjusted to the lower radius. For e (indexing to compute length), Conservative Entry causes the higher e-value to be used. Along the various stages of computation, numerical values may be rounded. This is simply rounding to the nearest evenly divisible number of the rounding value. For example, if e-rounding were set to 0.25, and e as it is computed from a table comes out to be 3.789, the value would be rounded to 3.75, which is evenly divisible by Guide: Setting Up Superelevation SEP Files

13 Terminology CALCULATION OVERVIEW This section describes the process used by Bentley Civil to calculate the superelevation from an engineering standpoint and explains how the various preference settings affect that process. The following is a flow chart showing the major stages which take place in the process of calculating superelevation in the order those stages take place. Using the radius of each curve, e-values are computed. Using the computed e-value, Runoff Lengths are computed as if the roadway had only two lanes. This Runoff Length is termed here Unadjusted Length. Using Unadjusted Lengths, true Runoff lengths (Adjusted Lengths) are computed based on the actual roadway widths (or number of lanes). Transition stations are computed using the true Runoff lengths. Curve Conflicts are then checked and corrected if possible. Finally, transition stations / cross slopes are used to draw the superelevation lanes in the design file. Guide: Setting Up Superelevation SEP Files 7

14 AASHTO Method 5 E COMPUTATION These preferences relate to e for each curve. Regardless of the manner of computation, e computation is based on the curvature of each curve and the Design Speed. OPTION E Method: Radius Table AASHTO Method 5 Equation Table name Speed Interpolation: Radius Interpolation: Linear Closest Entry Conservative Entry E Rounding Increment DESCRIPTION This option determines which method is used to compute e. AASHTO Method 5 or Radius Table - this field contains the name of the csv file in which to find the tables. If a path is specified along with the csv file name, that path will be used regardless of other methods of setting the path such as Environmental Variables. If the table cannot be found, an error message is displayed in the Message Center and no further tasks can be initiated. Equation - text field is the equation. Not utilized in SELECTseries 3, as the user selection is a pick list based on the design speeds in the SEP (and associated) files. Radius Interpolation only applies to the Radius Table option. This interpolation option specifies how Bentley Civil is to interpolate between Radius Rows if the given Radius does not have a corresponding row with an exact match in the table. Applies to e regardless of how it is computed.. This is simply rounding to the nearest evenly divisible number of the rounding value. For example, if e-rounding were set to 0.25, and e as it is computed from a table comes out to be 3.789, the value would be rounded to 3.75, which is evenly divisible by Set a value of 0.00 to disable the rounding of e. AASHTO METHOD 5 AASHTO Method 5 equations require inputs of Radius, Design Speed, Running Speed, Side Friction Factor, and e Max. When computing e via AASHTO Method 5, a table in csv format is utilized. One sample file is depicted below. [Urban] VR F E Min NC The first row contains the table name. There may be more than one table in each.csv file. The second row contains the Design Speeds. Note that the first cell of the second row is blank. In that this row contains Design Speeds, then, it acts as column headings for the rows below it. The first column of the remaining rows contains text which indicates what that row represents. The rows are Running Speed (VR), Side Friction Factor (F), e Max (E), and Minimum Radius for Normal Crown (Min NC). If the Min NC row is omitted from the table there is no problem. Computation simply proceeds without consideration for that feature. 8 Guide: Setting Up Superelevation SEP Files

15 Radius Table For any Design Speed, the radius of each curve is put into the AASHTO Method 5 equations, as are the values found in the table. For each variable, the value used in the equation is found by reading the cell found by matching the row of the variable name and the column of the design speed. RADIUS TABLE The following is a sample from a.csv file of the format used when e Method is set to Radius Table: [6% e Max] R min NC NC NC NC 5000 NC NC NC 3000 RC RC RC R min e Max The first row contains the table name. There may be more than one table in each.csv file. The second row contains the Design Speeds. In that this row contains Design Speed, then, it acts as column headings for the rows below it. Note that the first cell of the second row is blank. For the remainder of the rows, the data in the first column indicates the meaning of that row. There are three row types with text in the first column, known as parameter rows: R min NC, e Max, and R min. These rows may be placed anywhere after the Design Speed row so long as a radius row (having a number in the first column) is not both above and below any parameter row. The "R min NC" parameter indicates the minimum radius a curve may have while still having Normal Crown. The "e Max" parameter indicates the maximum superelevation rate for that Design Speed. This is the e value used in association with the "R min" parameter, which is the minimum allowable radius for the given Design Speed. If the "e Max" row is omitted, e Max is still utilized, but it is taken to be the e-value associated with the lowest radius for any given Design Speed. The rows with numbers in the first column are the radius rows, and the primary function of the table has to do with them. When Bentley Civil computes an e value in this method, it reads the table to find which radius row corresponds to the radius of the curve in question. Using the row of the radius and the column of the Design Speed, the Engine reads the value of the resulting cell. In the example table above, a Design Speed of 110 and a radius of 1000 would result in an e of 3.8. The values "NC" and "RC" found in the table have special meaning. NC is interpreted by Bentley Civil to be the Normal Crown slope as entered by the user at the Superelevation Computation dialog. RC is interpreted as negative one times the Normal Crown slope. Normal Crown is determined as the slope of the lanes closest to the Shape Cluster Tie. ASSUMPTIONS SPECIFIC TO RADIUS TABLE CSV FILES Radius values are in descending order as one reads downwards. Guide: Setting Up Superelevation SEP Files 9

16 Equation For a given design speed, all values are filled in from the largest radius down to the lowest applicable radius. In other words, no empty cells should be present for radii greater than the minimum. The parameter rows are not interleaved with the radius rows, although they may come before or after the radius rows. EQUATION In the e-computation stage, the following intrinsic variables are available: R Radius Dc Degree of Curve Vd Design Speed NC Normal Crown (in percent, include signage) When Equation is used to compute e, there is no way to indicate Minimum Radius, Maximum e, or Minimum Radius with Normal Crown. RUNOFF LENGTH SPIRAL The second step in the process of computing Superelevation transitions is the computation of Unadjusted Length, which is the Runoff Length as if the roadway had two lanes only. (Adjusted Length is the true Runoff Length, adjusted for the true roadway width.) In all methods of computation of Unadjusted Length, the computation is based on the rounded e value for each curve. If one or both sides of a curve (ahead and/or back) have a spiral, no length computations need to be made for the part with a spiral since the length of transition is dictated by the length of the spiral. Within the Spiral preferences, the user has the option to determine how spiral lengths are matched to Superelevation Transition lengths. If the option is set to Spiral Length = Runoff Length, the Runoff Length is the same as the spiral length. Runoff begins with the TS or CS and ends at the SC or the ST. Tangent Runout falls on the adjacent tangent, outside of the spiral. This option is depicted below. 10 Guide: Setting Up Superelevation SEP Files

17 Circular Curve (Unadjusted Length Computation) If the option is set to Spiral Length = Runoff Length + Tangent Runout, Runoff and Tangent Runout lengths are set such that the Total Transition Length equals the spiral length, and the Tangent Runout falls on the spiral. This option is depicted below. CIRCULAR CURVE (UNADJUSTED LENGTH COMPUTATION) The remainder of the items in the Runoff grouping have to do with Unadjusted Length computation for circular curves in which either the back, ahead, or both sides of the curve are not spirals. Runoff Length Method Table Name All methods for computation of Length use e and Design Speed as the primary inputs. The Length Method option button determines which method Bentley Civil will used to compute the Unadjusted Length. The supported methods are e Table, Relative Gradient Table, and Equation, each of which is detailed following the explanation of the dialog items. When the Method is AASHTO Method 5 or Radius Table, this field contains the name of the csv file in which to find the tables. Generally, no path should be given in the file name since these are controlled by Environmental Variables and/or user control in the Superelevation Computation dialog. If a path is specified along with the csv file name, that path will be used regardless of other methods of setting the path such as Environmental Variables. If Methodology is Equation, the text field is the location where the equation is entered. Pressing the Files button opens the dialog, wherein the desired file may be selected. Pressing the Edit button opens the editor specified in the environmental variable GPK_SUPER_EDITOR and should normally be set to Excel or some type of spreadsheet application. Speed Interpolation: Specifies how to interpolate between Design Speed columns if the user selects a Design Speed which is not found in the table. Speed Interpolation is applicable to e Table and Relative Gradient Table. E Interpolation: Linear Closest Entry Conservative Entry Width Basis: Nominal Lane Width Specifies how to interpolate between e Rows if the given e value does not have a corresponding row in the table. e Interpolation applies only to e Table. Linear Interpolation causes Bentley Civil to perform a straight-line interpolation between the two possible values. Closest Entry forces the computed value to equal a value found in the table. Which value to select is determined by how close the indexed number is to either of the two choices. For example, if radius equals 1150, but the closest values available in the table are 1200 and 1000, e would be computed based on the 1200 radius row because 1150 is closer to 1200 than it is to Conservative Entry forces the computed value to equal the more conservative of the index values. As an example, if Design Speeds of 60 and 70 are available, and a user enters a Design Speed of 62, the actual value would be set to 70 because it is more conservative than 60. For Design Speed, Conservative Entry causes the value to be adjusted upward. For radius, it causes the value to be adjusted to the higher radius. For e (indexing to compute length), Conservative Entry causes the higher e-value to be used. Width Basis is used by Bentley Civil to determine how to compute Unadjusted Length if the inside lane has a width differing from Nominal Lane Width. Guide: Setting Up Superelevation SEP Files 11

18 Circular Curve (Unadjusted Length Computation) Actual Lane With As an example let us consider a Typical Section with four lanes and no median. The inside two lanes are ten feet wide and the outside two lanes are fourteen feet wide, while the Nominal Lane Width is twelve feet. If Width Basis option is set to Nominal Lane Width, and the value read from the table (or equation) is 35, no change is made to that value. If Width Basis option is set to Actual Lane Width, and the value read from the table (or equation) is 35, that value is multiplied by 12 over 10, resulting in an Unadjusted Length of 42. Consider Half Lane If Width < It is common that five or seven lane roadway sections have the crown point in the center of the middle lane. In order to model this correctly, that middle lane must be represented as two lanes, each being half the true lane width. Several options which adjust the runoff length must have an accurate count of the number of lanes. By modeling a five lane section with six lanes, this count is not correct. This situation is resolved by specifying a width below which a lane is counted as a half lane. In this way, the five lane section modeled by four full lanes and two half lanes is correctly considered by Bentley Civil to have five lanes. As an example, if the center turn lane of a roadway were 16 feet wide, the left and right halves of the center turn lane would each be 8 feet. If the Consider Half Lane if Width < text field were set to 8 (or 9 or any number greater than or equal to 8), those two lanes would be considered together as one lane for the purpose of counting lanes in preparation for making the Runoff Length Adjustment. Runoff Rounding The value in Length Rounding Increment applies to Unadjusted Runoff Length regardless of how it is computed. See the Overview section for an explanation of rounding. E TABLE e Tables compute Unadjusted Length by indexed Design Speed versus e. The following is a sample from a.csv file of the format used when Length Method is set to e Table: [8% e Max] The first row of the table contains the table name. There may be more than one table in each.csv file. The second row contains the Design Speeds. In that this row contains Design Speed, then, it acts as column headings for the rows below it. Note that the first cell of the second row is blank. For the remainder of the rows, the first column represents e value, by which Unadjusted Length is to be indexed. Bentley Civil reads this table as follows: The cell is located which correspond to the Design Speed and the (rounded) e. If a number exists at that cell, it is used as the unadjusted length. If no number is present in the cell, the Unadjusted Length is computed by interpolating between the next cell above and below which do contain values. If the next non-empty-cell upward is the Design Speed, then the next non-empty-cell downward is treated as the minimum length. 12 Guide: Setting Up Superelevation SEP Files

19 Circular Curve (Unadjusted Length Computation) Here are four examples to illustrate this. Example 1: With a Design Speed of 110 and e of 7.2, an exact match is found yielding a value of 62 for Unadjusted Length. Example 2: With a Design Speed of 120 and e of 7.0, no value is found in the corresponding cell. No other values of e are found above that cell, so the next value downward is taken as the minimum. The value returned for Unadjusted Length is 67. Example 3: With a Design Speed of 100 and e of 7.5, no cell corresponds. The next value found upwards is 56 for e of 6.9. The next value found downward is 61 for e of 7.6. The value would be computed based on the e-interpolation option. Saying that the e-interpolation option was set to "Linear", the value would be computed as This number would possibly be rounded depending on the Unadjusted Length Rounding value. Example 4: With a Design Speed of 120 and an e of 3.5, this value of e is not found on the table at all. The first non-empty-cell under the Design Speed is taken as the value of Minimum Length. Therefore the Unadjusted Length is returned as 67, the minimum. ASSUMPTIONS SPECIFIC TO CURVATURE TABLE.CSV FILES E values are in ascending order as one reads downwards. The first non-empty cell for any given Design Speed is the minimum length for the entire Design Speed. Unlike the Radius Table, the e table may have blank cells interleaved with non-blank. If cells are left blank, interpolation is performed between values of non-blank cells. RELATIVE GRADIENT TABLE The Relative Gradient Table can also be referred to as "Relative Profile Gradients". The Relative Gradient Table appears as follows: [Urban] L Min RG The first row contains the Table Name. There may be more than one table in each.csv file. The second row contains the Design Speeds. In that this row contains Design Speeds, then, it acts as column headings for the rows below it. Note that the first cell of the second row is blank. The first column of the remaining rows contains text which indicates what that row represents. The rows are Minimum Length (L Min) and Relative Gradient (RG). For any Design Speed, the corresponding Relative Gradient is read from the table to be used in the following equation: Length = Nominal_Lane_Width * e / RG Length is then checked against L Min. If Length is less than L Min, Length is increased to equal L Min. It is important to note that when the Distribution Over option (found on the Distribution tab) is set to Tangent Runout + Runoff Length (which means Distribution Percentage is applied to the Total Transition Distance), all Unadjusted Lengths as reported in the Activity Log still represent Runoff Lengths. However, the values in this case are prorated so the L Min value applies to Total Transition Guide: Setting Up Superelevation SEP Files 13

20 Circular Curve (Unadjusted Length Computation) EQUATION Length. As an example, a curve has e of 6 and NC of 2. The Unadjusted Length must result in a Total Transition Distance of 33 (since 33 is L min in the table). The value returned as Unadjusted Length would be (even if Length Rounding were 1.0), resulting in the Total Transition Length specified as L min in the table. In the Unadjusted Length computation stage, the following intrinsic variables are available: e superelevation rate (in percent) Vd Design Speed NL Number of Lanes Wa Actual Roadway Width Wn Nominal Lane Width NC Normal Crown (in percent, include signage) Xm Maximum Cross Slope (in percent, include signage) When Equation is used to compute Unadjusted Length, there is no way to indicate Minimum Length. TANGENT RUNOUT Tangent Runout is the distance from a Cross Slope of Normal Crown to a Cross Slope of zero as depicted here: Three methods are available to compute Tangent Runout Length: By Relative Gradient, Fixed Distance, or Equation. TANGENT RUNOUT DISTANCE BY RELATIVE GRADIENT When the Tangent Runout Distance option is set to By Relative Gradient, the Tangent Runout Distance is computed as the result of applying the Relative Gradient of the Runoff to the Tangent Runout as depicted below. 14 Guide: Setting Up Superelevation SEP Files

21 Circular Curve (Unadjusted Length Computation) Note that this method causes a continuous Relative Gradient for the entire transition. TANGENT RUNOUT DISTANCE - FIXED DISTANCE When the Tangent Runout Distance option is set to Fixed Distance, a second parameter is used which contains the numeric value for the distance. With this option, Tangent Runout Length is set to a certain distance without regard to the Relative Gradient of the Runoff. As depicted in the image below, the distance is that from Normal Crown to the flat slope. Observe that this causes a discontinuity in the Relative Gradient at the zero slope point. If the Typical Section has broken back cross slopes, Normal Crown is considered to be the value of the Cross Slope of the lanes adjacent to the Tie. This is the lane which has its Tangent Runout Length set to the Fixed Distance. Lanes with Normal Slopes other than Normal Crown have their Tangent Runout Distance prorated. TANGENT RUNOUT DISTANCE - EQUATION When computing Tangent Runout Length by equation, the following intrinsic variables are available: e Superelevation Rate (in percent) Vd Design Speed NL Number of Lanes Wa Actual Roadway Width Wn Nominal Lane Width NC Normal Crown (in percent) Xm Maximum Cross Slope (in percent) La Adjusted Runoff Length Lu Unadjusted Runoff Length Guide: Setting Up Superelevation SEP Files 15

22 Circular Curve (Unadjusted Length Computation) LR Length Adjustment Ratio* RG Relative Gradient of Runoff Portion of the Transition * The Length Adjustment Ratio is Adjusted Runoff Length Unadjusted Runoff Length Note that for spiraled curves, Unadjusted Length and Adjusted Length both equal the Spiral Length regardless of what length value is computed for the curve and regardless of the roadway width. Further, this means that for spirals, Length Ratio always equals 1.0. In the Adjust Factor grouping, if the value for the given number of lanes is a value other than 1.0, the Length Adjustment Ratio equals the Adjust Factor. If the value for the given number of lanes is set to 1, the Length Adjustment Ratio is Actual Roadway Width 2 x Nominal Lane Width Depending on the equation entered by the user, it is possible that there will be a discontinuity in the Relative Gradient at the zero slope point. TOTAL LENGTH ROUNDING INCREMENT After the Tangent Runout has been computed (regardless of the method), Total Length Rounding is applied if specified as something other than zero in the Total Length Rounding text field. If rounding takes place and the Tangent Runout Distance option is set to By Relative Gradient, the length change caused by the rounding is applied evenly to both Runoff and Tangent Runout such that the Relative Gradient remains the same over both portions of the transition. If the Tangent Runout Distance option is set to Fixed Distance or Equation, the length change is applied entirely to the Runoff portion so that the Tangent Runout distance remains unchanged. ADJUSTMENT FACTORS The user can control Adjustment Factor settings for three lanes up to twelve lanes. If a roadway has more than twelve lanes, the length adjustment is made according to the settings for twelve lanes. BASE ADJUST FACTOR ON: OPTION Two options are supported for the Baseline of the Adjustment Factor: Total Number of Lanes (default option) - The multilane adjust factor is determined by the total number of lanes across the entire roadway. Number of Lanes Rotated (Compliant to AASHTO Standards). The multilane adjust factor is determined by number of lanes being rotated on one side of each roadbed. Roadbed Configuration Total Number of Lanes Number of Lanes Rotated Guide: Setting Up Superelevation SEP Files

23 Circular Curve (Unadjusted Length Computation) 4 1 MULTILANE RUNOFF LENGTH ADJUST FACTORS Length Adjustment is a modification of the two-lane length (unadjusted length) according to the true width of the roadway. The length is adjusted by applying a multiplier according to the number of lanes. DISTRIBUTION After Adjusted Lengths have been computed for non-spiraled ends of circular curves, the transition is distributed over the curve and its adjacent tangents and stationing is computed relative to the PC and PT. The amount of the transition which falls on the tangent is termed Percent on Tangent. Options are provided to base that percentage on Total Length or on Runoff Length. The following image depicts distribution based on Runoff Length (Distribute Over : Runoff Length Only). The following image depicts distribution based on Total Transition Length (Distribute Over: Tangent Runout + Runoff Length.) UNDIVIDED VS. DIVIDED ROADWAY Two separate sets of preferences are supported which both contain items for Distribute Over and % On Tangent. The two sets, Undivided Roadway and Divided Roadway (High Side), enable the user to Guide: Setting Up Superelevation SEP Files 17

24 Circular Curve (Unadjusted Length Computation) have different Distribute Over and % on Tangent options depending on the Facility setting on the Calculation Dialog. DISTRIBUTE OVER The Distribute Over option controls whether Bentley Civil applies the % on Tangent value to Runoff Length or Total Transition Length. If set to Runoff Length Only, the distribution percentage is applied to the Runoff Length. If set to Tangent Runout + Runoff Length, the distribution percentage applies to the Total Transition Length. % ON TANGENT The % on Tangent fields determines the percentage of the distribution which is to be located on the tangent leading up to (or trailing) the curve. DIVIDED ROADWAY (LOW SIDE) Within the Divided Roadway (Low Side) group box are preferences for Match High Side Super Station and Distribution. If the Match High Side Super Station is specified, the Superelevation Transition on the low side (inside of the curve) is stationed such that the Full Super station for the low side is the same as for the high side (outside of the curve). This is depicted in plan view in the following image: If Distribution is specified, the transition stations for the low side are computed without correlation to the high side stationing. The low side transition stations are computed according to the corresponding % on Tangent value. This is depicted in plan view in the following image: 18 Guide: Setting Up Superelevation SEP Files

25 Circular Curve (Unadjusted Length Computation) STATION ROUNDING Station Rounding takes place within the superelevation computation process immediately after Transition Distribution and applies to the stations computed during Transition Distribution. There are four options available for station rounding as detailed in the table below. No Rounding Leaves the transition stations unaltered. Round Full Super Stations Shifts the transition stationing such that the Begin and End Full Super Stations fall on even numbered stations according to the value entered into the Even text field. Other stations of the transition are shifted by the same amount so that the Relative Gradient does not change because of the adjustment. The stationing may be made higher or lower depending on which even station is closer. ROTATION Round Normal Crown Stations Round All Stations Shifts the transition stationing such that the End and Begin Normal Crown Stations fall on even numbered stations according to the value entered into the Even text field. Other stations of the transition are shifted by the same amount so that the Relative Gradient does not change because of the adjustment. The stationing may be made higher or lower depending on which even station is closer. Rounds both End and Begin Normal Crown Stations as well as Begin and End Full Super stations such that all of those transition stations fall on even stations as even is defined in the text field. Full Super stations are shifted toward the PI station of the curve and Normal Crown stations are shifted away from the PI station of the curve. This is because rounding all of these stations requires that the Relative Gradient be changed. Rounding in this manner insures that the Relative Gradient adjusts downwardly, yielding a more conservative, less steep value. TRANSITION PROFILE PARABOLIC LINEAR The Elevation Transition (Profile) has options for Parabolic or Linear. If the option is set to Parabolic, the Transition ID option on the Superelevation Computation dialog is unghosted. With that option, it is possible to specify Transition ID's other than Linear. When attaining superelevation with linear transition, two modes of transition are supported to control roadways with broken back slopes or divided roadways with a double roof top configuration. Linear transition by slope Linear transition by elevation Guide: Setting Up Superelevation SEP Files 19

26 Circular Curve (Unadjusted Length Computation) Divided roadway with double roof top configuration Roadway with broken back slopes These two modes yield the same result for undivided two lane roadways or multilane roadways with uniform cross slopes. TRANSITION BY SLOPE This is the default option. The transition is such that the slope diagram is continuous, smooth and linear from the level section to the fully superelevated section. TRANSITION BY ELEVATION EXAMPLE The term Elevation means normalized delta elevation. The transition is such that the normalized elevation diagram is continuous, smooth and linear from the level section to the fully superelevated section. The following example is based on a normal section of a divided roadway with the rotation point located at the inside edge of pavement, 10 lane width and a 2% normal crown slope. Assuming a left turn, the relative elevation diagram of the outside (high side) roadway and its corresponding slope diagram are shown below. 20 Guide: Setting Up Superelevation SEP Files

27 Outside Lane Rotation Top: Delta elevation diagram of the outside (high side) Bottom: Corresponding slope diagram For the outside lane edge point delta elevation line to have a linearly smooth transition, the lane slope line must have a kink at the reverse crown point to compensate. This is due to the change in width of the overall rotation after the RC point. The inside (low side) roadway s corresponding relative elevation diagram and slope diagram are shown below. Top: Delta elevation diagram of the inside (low side) Bottom: Corresponding slope diagram Similarly, to achieve a linearly smooth delta elevation transition line for the outside lane point of the outside roadway, an extra superelevation transition slope must be inserted at the outside lane of the outside roadway OUTSIDE LANE ROTATION Outside Lane Rotation has two options: Rotate to Match Inside Lanes and Independent Rotation. When the option is set to Independent Rotation, all transition stations begin and end at the same station, regardless of Normal Cross Slope. If the Typical Section has Broken Back Normal Crown, this means that the cross slope remains broken throughout the transition until Full Super is achieved, at which point the cross slope is continuous. When the option is set to Rotate to Match Inside Lanes and the Typical Section has Broken Back Normal Crown, the lanes of lesser cross slope do not begin transitioning until the lanes with greater cross slope come up to match. In other words, as soon as possible within the transition, the cross slope is unbroken. AXIS OF ROTATION The Axis of Rotation option only applies to two lane roadways. The only option is Rotate About Centerline. Note The option to Rotate About Inside Edge is NOT supported in SELECTseries 3. If you need this feature, you ll need to use the SRL file, which does support it. Guide: Setting Up Superelevation SEP Files 21

28 Overview SUPERELEVATION TRANSITION CONFLICT RESOLUTION OVERVIEW Superelevation Transition Conflicts occur when the stationing of the superelevation transitions of two adjacent curves overlap, or when the fully superelevated station range on one curve is too short. When curve conflicts occur, Bentley Civil attempts to resolve them by adjusting relative gradients, distribution percentages or e values, depending on the applicable preferences. Before augmenting the superelevation lanes with calculation data, Bentley Civil scans the superelevation transition stationing created by prior processes in the superelevation flowchart for conflicts. Four types of conflicts are scanned for: Reverse Curves, Broken Back Curves, Compound Curves, and Short Curves. The Reverse Curve conflict occurs when two adjacent curves which deflect in opposite directions have transitions which overlap, or which have a short section of full Normal Crown between them. The Broken Back conflict occurs when two adjacent curves which deflect in the same direction have transitions which overlap, or which have a short section of full Normal Crown between them. The Compound Curve conflict happens when two curves deflecting in the same direction have no intermediate tangent, resulting in a PCC shared between them. The three previous Curve Conflicts have to do with two adjacent curves. The final Conflict of the four, Short Curve, has to do with only one curve. It is the case in which the length of the fully superelevated segment of the curve is too short. METHODS OF DISTRIBUTING MODIFICATIONS The various options available to resolve conflicts all involve changing the stations in some way such that the conflict disappears. Some options change the Normal Crown and Full Super stations equally which is in essence sliding the transition while leaving the Relative Gradient unchanged. Other options hold the Full Super stations constant while changing the Normal Crown stations. This has the effect of changing the Relative Gradients, making them steeper. Other options may be characterized as merging the transitions of the two conflicting curves into one single transition. In many of the resolution cases, it may be desirable to distribute the amount of change based on the characteristics of the two curves. For example, it is possible to cause the station adjustments in Reverse Curves to be greater for the curve with the greater Degree of Curve, the lower Radius, or the greater e value. MULTIPLE CONFLICTS It sometimes happens that two superelevation conflicts may happen on the same or adjacent curves. Therefore, when double conflicts occur, Bentley Civil prioritizes them as which takes precedence, as follows: Reverse Curves Broken Back Curves Compound Curves Short Curves This means, for example, that if there is a choice to be made as to whether to fix the Reverse Curve situation or the Broken Back Curve, Reverse Curves are fixed. 22 Guide: Setting Up Superelevation SEP Files

29 Spirals SPIRALS With two exceptions, no curve conflicts alter stationing on a spiral. This means that if there is a conflict between a spiraled curve and an unspiraled curve, all of the modification required to resolve the conflict are applied to the unspiraled curve. The first exception to this is when a conflict resolution alters the superelevation rate coming in to a spiral. This may happen when a short curve situation is resolved by the Truncate e option, or when a broken back curve situation is resolved by Lower e to Reverse Crown or Hold Lower e Through Transition. In such cases, the superelevation transition does not begin or end (as the case may be) at the spiral control station, but at the prorated station necessary to maintain the Relative Gradient which was along the spiral before the adjustment. The second exception to the statement that no curve conflicts alter stationing on spirals is the case where two spirals conflict with each other such as the situation of short or zero-length tangents between two spirals. In these cases the changes in the transition stationing is such that the relative gradient of the spiral is maintained. REVERSE CURVES Reverse Curves occur when two adjacent curves which deflect in opposite directions have superelevation transitions which overlap or are in close proximity. Two levels of conflict are defined for Reverse Curves: Critical and Supercritical. The determining factors for defining a conflict as Critical or Supercritical are both based on the Length of Normal Crown existing between the two transitions. (Note that overlapping transitions may be considered to have a negative Length of Normal Crown.) The distinction, then, between Critical and Supercritical has to do with how the conflict is handled. If the conflict is Critical, adjustments are made so that the Minimum Normal Crown Length is maintained. If the conflict is Supercritical, the transitions of the two curves are merged and Normal Crown never occurs between the conflicting curves. When Bentley Civil checks for this conflict, it first checks to see if the Length of Normal Crown violates the Supercritical threshold. If it does not, Bentley Civil then checks the Critical threshold. This means that if the value for Maintain Minimum Length is less than or equal to Supercritical Length, no conflict would ever be handled as Critical. Also note that either value may be negative, although this is ill-advised for Maintain Minimum Length. CRITICAL CASE As stated before, if the Length of Normal Crown in a Reverse Curve conflict is less than the "Maintain Minimum Length" value and greater than the "Supercritical Length" value, the conflicting transitions are adjusted so that the Length of Normal Crown equals the Maintain Minimum Length value. This situation is depicted here as it exists before adjustments are made. Guide: Setting Up Superelevation SEP Files 23

30 Supercritical Case TREATMENT Two options are available for how the Critical case is treated: Hold Relative Gradient, Slide Transition Stations and Hold Full Super Stations, Change Relative Gradient. HOLD RELATIVE GRADIENT, SLIDE TRANSITION STATIONS When the Treatment option is Hold Relative Gradient, Slide Transition Stations, both Full Super Stations and Normal Crown Stations are shifted equal distances so that the Relative Gradients do not change, as depicted below: HOLD FULL SUPER STATIONS, CHANGE RELATIVE GRADIENT When the Treatment option is Hold Full Super Stations, Change Relative Gradient, the Normal Crown Stations are changed but not the Full Super Stations. This results in the Relative Gradient being steepened: SUPERCRITICAL CASE If the unadjusted Length of Normal Crown in a Reverse Curve conflict is less than the Supercritical Length value in the Supercritical group box, the conflicting transitions are merged such that Normal Crown is bypassed. The approach Bentley Civil takes to accomplish the transition merging depends on three options: Treatment, 0% Positioning, and Relative Gradient, each of which is described here. 24 Guide: Setting Up Superelevation SEP Files

31 Supercritical Case TREATMENT Four options are supported for the treatment of Supercritical Reverse Curves as detailed below. COMBINE TRANSITIONS; HOLD FS STATIONS The End Full Super Station of the first curve and the Begin Full Super Station of the second curve are not changed. The transition goes directly from one station to the other. The Relative Gradient changes as a result of the adjustment. COMBINE TRANSITIONS; POSITION 0%, SPECIFY RELATIVE GRADIENT The End Full Super Station of the first curve and the Begin Full Super Station of the second curve are adjusted. The new Relative Gradient of the resulting combined transition is determined according to the Relative Gradient option further down on the dialog. The position of the 0% station is determined by the 0% Positioning option immediately below on the dialog. Guide: Setting Up Superelevation SEP Files 25

32 Supercritical Case KEEP TRANSITIONS DISTINCT; POSITION 0%, HOLD FS STATIONS The End Full Super Station of the first curve and the Begin Full Super Station of the second curve are not changed. The 0% Position is determined by the 0% Positioning option. Relative Gradients change as a result of the adjustment. KEEP TRANSITIONS DISTINCT ; POSITION 0%, HOLD RELATIVE GRADIENT The Relative Gradients of the transitions are unchanged. The 0% Position is determined according to the 0% Positioning option. The End Full Super Station of the first curve and the Begin Full Super Station of the second curve are changed in accordance with the 0% Position and the Relative Gradients. 0% POSITIONING Four options are available for the 0% Positioning option. These options are used to determine the location of the 0% slope along the tangent between curve 1 and curve 2. If this distance is zero (from a PRC), the 0% point is placed at the PRC. The four options determine how to weight the placement along the tangent. If the option is Evenly, the 0% point is placed at the midpoint of the intervening tangent. If the option is By Degree of Curvature, the 0% point is placed along the tangent at a distance ratio which is the same as the ratio of the Degrees of Curvature of the two curves. If the option is By Radius, the 0% point is placed along the tangent at a distance ratio which is the same as the ratio of the Radii of the two curves. If the option is By e, the 0% point is placed along the tangent at a distance ratio which is the same as the ratio of the e-values of the two curves. 26 Guide: Setting Up Superelevation SEP Files