Geometric Layout for Roadway Design with CAiCE Visual Roads

Transcription

1 December 2-5, 2003 MGM Grand Hotel Las Vegas Geometric Layout for Roadway Design with CAiCE Visual Roads Mathews Mathai CV32-3 This course describes and demonstrates various tools for defining horizontal alignments, vertical alignments, roadway edges, medians and islands, intersection details, and other elements of roadway design geometry. About the Speaker: Mathews earned both bachelor's and master's degrees in Computer Science and graduated with honors from the Florida Institute of Technology. He has 12 years of experience in civil engineering and surveying automation. He joined CAiCE at Autodesk in 1992 and is currently the product manager for the Visual Roads product. Mathews has worked in several positions at CAiCE with Autodesk including software and application development, technical support, sales/marketing, and software training.

2 Introduction to Visual Roads CAiCE Visual Roads CAiCE at Autodesk designs and develops software solutions for transportation engineering projects. CAiCE products address surveying, topographic mapping, digital terrain modeling, roadway design, right-of-way engineering, drainage engineering, landscape architecture, and construction applications. CAiCE users include many state departments of transportation in the United States, several transportation ministries in Canada, municipal and county public works departments, and engineering and surveying companies throughout North America and elsewhere. Visual Roads is the CAiCE product that is used for highway design engineering. It provides the highway designer with tools to develop detailed models of proposed transportation facilities. It uses a design modeling approach that lets the engineer develop horizontal and vertical geometry, analyze design parameters and safety constraints, create cross sections and 3-D models of the proposed highway, draw three dimensional models of the proposed design, and utilize the models for engineering calculations and plans production. CAiCE Roadway Design Models The product of the Visual Roads design process is a cross section file. Cross sections form a model of the proposed roadway by storing surfaces that are perpendicular to an alignment. Each surface has a feature code and consists of a collection of straight-line links. There is no limit to the number of stations, the number of surfaces, or the number of links within a surface. Also, surface links may be non-contiguous. For example, the surface that represents paved finish grade on a divided highway will have two separated sets of links. Each point on a surface is defined by an offset, an elevation, and a point feature code. Surfaces in a cross section file may represent existing ground, topsoil stripping and existing sub-surfaces, paved and unpaved finished grade, various paving layers, structures such as guardrails, retaining walls, curbs, and underdrains, or any other item that is needed. Figure 2 shows an example of a cross section that contains many of these features. Service road with raised curb and sidewalk Expressway with depressed median and raised curb Retaining wall Existing ground Guardrails Figure 2 - Cross Section Example 2

3 Elements of Roadway Design Modeling Several elements must be in place before the cross section models can be created. The required elements are horizontal geometry, vertical geometry, superelevation design, existing terrain cross sections, and a library of typical cross section components called fragments. Horizontal Geometry The geometric layout is defined using the database object called a geometry chain, which is a connected series of point, curve, and spiral elements. A geometry chain can represent any type of two-dimensional curvilinear entity, and is typically used for centerlines, pavement edges, shoulder edges, traffic islands, medians, right-of-way boundaries, property boundaries, driveways, and sidewalks. Geometry chains that are used for alignments can have stations and station equalities. The minimum requirement for horizontal geometry is an alignment for each roadway. Creating an alignment involves a considerable amount of engineering analysis to ensure that it meets design standards for safety and driver comfort. For example, given a particular design speed, the alignment must comply with certain criteria for minimum curve radius, length of spirals, and minimum distance between curves. Visual Roads provides numerous tools that provide built-in, customizable checks for compliance with each user s design criteria. Vertical Geometry Vertical geometry is defined using the design profile object. The profile defines the elevation of the road s profile grade line (PGL) point at each station on the alignment. Additional profiles may be needed to define elevations for retaining walls, ditches, ramps, and other roadways. Visual Roads includes tools that help you check for minimum curve length, sight distance compliance, and vertical clearances. Superelevation Design Superelevation design consists of specifying the design slopes for travel lanes and shoulders throughout the project. Roads typically use a 2% downward slope from the crown of road or edge of pavement to ensure proper drainage. The roadway is superelevated, or banked, as it goes around curves in order to resist centrifugal forces acting on the vehicle. The different methods used for determining superelevation can be quite complex, but the end result is simply that the travel lane and shoulder slopes are defined at any station on each alignment. Superelevation definitions are attached to each horizontal alignment chain, allowing each roadway to have its own, independent slope definitions. Existing Surface Sections Existing surface sections are the cross section surfaces that represent the existing terrain and subterranean features, and are usually derived from digital terrain models. These are the initial set of surfaces that go into the roadway design model. Feature coded points on the terrain surface allow you to mark the locations of critical features such as crowns, pavement and shoulder edges, ditch lines, and catch points. Depending on the detail required, the existing surfaces may also define topsoil stripping, existing pavement, and geotechnical sub-surfaces such as sand, gravel, and rock. Roadway Design Modeling using Fragments CAiCE Visual Roads utilizes a unique technology called fragments to build proposed cross section surfaces. A fragment is a VBA macro that adds surfaces for a particular type of roadway component, such as a median, travel lane, paved shoulder, ditch, or catch slope. Each fragment has its own set of input parameters that lets the engineer vary design values such as lane width, 3

4 subgrade depth, and grade. Because they are macro-based, an organization can build a library of fragments that has their own roadway types and design standards built into the program logic. For example, a state department of transportation can build a shoulder fragment that matches their own design criteria for geometric shape, pavement types, and behavior in different situations. A sample fragment description is included in the Appendix. Roadway design takes place in an interactive session where you can select fragments, set their input parameter values, and insert them to create the model of the proposed roadway. This process is done in a special cross section view window. To begin the session, you must load the existing surface cross sections and define a Profile Grade Line (PGL), which consists of a horizontal alignment and design profile. The PGL defines the offset and elevation of the design surface starting point at each station. The design session window shows all existing surfaces and the location of the PGL. It also places left and right hook points at the PGL location. The hook points define the starting point for surfaces inserted on the left and right side by the fragments. As each fragment is inserted, the hook points move to the location needed to start the next fragment. Figure 3 shows a design session window where the first fragment was inserted for a depressed median with paved shoulders, followed by standard travel lane fragments on each side. These particular fragments are from the library created to follow Michigan DOT standards. The two hook points were originally located at the PGL. After the depressed median fragment was inserted they moved to the inside edges of travel way, which mark the beginning positions for the travel lanes. After inserting the travel lane fragments, they moved to the outside edges of travel way, where they stand ready to locate a shoulder or curb and gutter. Once the entire section has been built, you can save the sequence of fragments with their input values as a template that can be run at other stations in batch mode. This does not necessarily create sections with identical geometry, as conditions change at each station. Running a template merely repeats the insertion of the fragments used at the original station. The same fragments adjust automatically for differences in profile grade, cut or fill conditions, superelevation changes, and changes in lane or shoulder widths. Figure 3 Interactive Cross Section Design 4

5 Horizontal Geometry Layout Horizontal Alignment Editor This feature is designed specifically for storing the types of chains that would be used as centerline alignments. It stores a series of PI s with a curve or spiral-curve-spiral at each PI. Although you can use this command to store a chain consisting only of points, you cannot store a chain where tangent links are not tangent to adjacent curve or spiral links. The Edit Horizontal Alignment dialog box uses a spreadsheet to define the chain geometry. At any time during editing, you can draw the alignment as currently defined in the spreadsheet by clicking the Draw button. Each row of the spreadsheet defines a single PI in the chain. The data items that define each PI are the point name, Easting, Northing, curve radius, spiral length back, spiral length ahead, and station. In addition, each cell in the spreadsheet contains a Picker control. The picker control button is only visible if you have clicked on or highlighted a particular cell. Any of the picker control menu items can be used to set the value for that cell in the spreadsheet. 5

6 The PI s can be defined by snapping to existing points, by on-screen digitizing, or by calculations from numeric input. Creating Parallel or Tapered Geometry You can store a geometry chain that is a parallel offset from an existing geometry chain with the command Geometry=>Geometry Chains=>Store Offset Parallel Chain. The new chain(s) can be at any plus or minus Horizontal Offset from the existing one. A list of horizontal offset values separated by commas can be given to define multiple offset chains. The Vertical Offset field is not used for geometry chains. Horizontal offsets can be defined either as distance values or as point names. If a point name is given, then the offset used is the perpendicular distance from the original chain to the point The SnapL button allows you to snap to a list of points to define multiple offset chains. Tangent links in the new chain will have the same length and direction as in the original chain. The offset chain s curves are concentric to the those in the original chain. For spirals, a special nonspiral figure is calculated that maintains a constant parallel offset from the spirals in the original chain. The offset chain can be created from a portion of the original chain. A Station Range can be defined by giving either a station value or point from the chain list for the Min. and Max. values. 6

7 Geometry Layout Tool This feature is used to create any Geometry Chain that the user desires. It can be either a Closed Chain or an Open Chain. This feature is used to create Interchange/Intersection ramps using intersecting chains as reference points to begin and end each ramp. The chain could be created from either end working toward the middle. If the Closed Chain option is selected, hook points are established at a single point with directions of each hook point opposite and parallel with the selected alignment. The user may build the chain in either direction from Hook Point 1 or Hook Point 2. These can be traffic islands, divided highway medians or any other closed chains. This macro requires only one alignment. It uses only one Station and Offset value to create the beginning and ending points; in other words, the same point. However, they are stored as two points with identical coordinates. These two points are being designated as "Hook Points". The initial direction of Hook Point 1 is in the same direction as the alignment. The initial direction of Hook Point 2 is 180 from the direction of Hook Point 1. If the Open Chain option is selected, one hook point is established at a single point with the direction parallel with the selected alignment. The chain can only be build from hook point 1 (Starting Point) Hook Point 2 is deactivated in this case. When using the Build Chain command, various dialog boxes are displayed so that the user can add tangents, curves, and spiral as needed to create a chain incrementally. After each segment is added, the hook point moves to the end of that element that was just inserted. The user can switch hook points at any time, building from either hook point. 7

8 Procedure: Enter the name of the Alignment centerline or select it with Snap. Enter the Station along the Alignment where the chain is to begin/end and the Offset to that point. Alternately, Digitize the starting point or Snap to an existing point which becomes both Hook Point 1 and Hook Point 2. The station and offset values are inserted into the appropriate text boxes. You may modify these values manually to round them to even values if you so desire. Enter the Feature Code to be stored with the chain. Select Set Hook Points to establish these Station and Offset values internally. The result will show the X and Y coordinates of Hook Point 1 and its direction. There will be two arrows drawn; one at each Hook Point. The active arrow is yellow (or current Highlight color) which indicates where the next link is to be added. The passive arrow is red. During the design process, the active Hook Point can be changed which switches the color of both hook points. Select Build Chain to switch to the Design Chain Control form. When the design is completed, control returns to this form. Select Reject Chain to discard the entire chain including points, curves, spirals, and spiralcurve-spirals that were stored in the Design process. Select Store Chain to permanently save the chain as a geometery chain that was calculated in the Design process. Select Close to exit the macro. However, it is very convenient at this point to enter another chain without closing the macro. Any number of chains may be done at one execution of this macro. Connecting Chain Builder The Connecting Chain Builder macro is used to create a geometry chain along the edge-oftraveled-way (ETW) in one quadrant between two intersecting roadway centerlines. It is designed to handle fairly simple cases involving tapering offsets for turning lanes connected by a single circular curve. Optionally, a parallel link may be inserted on either or both ends of the curve. The macro dialog box has fields that specify the parameters for the ETW relative to each of the intersection centerlines, and radius of the curve connecting between. For each of the centerlines the following items are needed. C/L Chain The name of the intersecting centerline chains. +/- ETW Offset The parallel offset from the centerline to the normal edge of travelled way. Taper Length (MTL, CTL) The length, parallel to the centerline, through which the tapering offset is applied. Taper Offset (MTO, CTO) The width of the turning lane, measured from the ETW. Parallel Length (MPL, CPL) The length of the line between the end of the taper and the beginning of the fillet curve in addition you must also define these items: Curve Radius The radius of the fillet curve. Clicking the Preview button computes and views the connecting chain in one of the intersection quadrants based on the input values provided. Note that the ETW offsets are signed values, where negative offsets are to the left of the centerline chains. The combination of positive and negative ETW offsets specify which of the four intersection quadrants you are working with. If intersecting ETW chains are being used instead of the centerlines, then a minimum offset of is required in order to determine the quadrant. 8

9 Previewing does not store any objects in the database. You may change input values and update the graphics by clicking Preview again. The Clear Preview button clears the preview graphics from the screen. If parallel lengths are given, then the radius line from CC to PC (BC) and the radius line from CC to PT(EC) are perpendicular to their respective chains. If no parallel lengths are given, the radius lines are perpendicular to the tapered links. If all taper lengths, offsets, and parallel lengths are set to zero, then the chain degenerates to a simple fillet curve. Once you are satisfied with the previewed results, you can store the connecting chain by clicking the Store button. This saves the chain and its components to the project database, clears the preview graphics, and redraws the stored chain. Once the current chain has been stored you can change input values and Preview and Store additional chains. 9

10 Vertical Alignment Editor Vertical Geometry Layout The primary method of creating and modifying design profiles is with the Geometry=>Profiles=>Store/Edit command. Defining VPI s by Numeric Input You can define VPI points through numeric input simply by typing values into the spreadsheet cells for Station, Distance, Elevation, Grade, LB (curve length back), and LA (curve length ahead). If you enter a distance, the station of the VPI is calculated as the station of the previous VPI plus the distance. If you enter a grade, the elevation of the VPI is calculated by applying the grade to the distance from the previous VPI. These calculations occur when you click the Draw button. The first VPI must be defined by a station and elevation value. The first and last VPI s must both have zero or blank vertical curve lengths. Defining VPI s by Digitizing 10

11 On-screen digitizing operations include digitizing a VPI location on the profile grid with the Digitize button and moving an existing VPI location with the Move VPI button. When moving a VPI, you can set the Snap Locks for freehand moving (None), holding the current Station, holding the current Elevation, shifting the VPI along its Grade Back or along its Grade Ahead. It is permissible to have two adjacent VPI s with the same station and different elevations to account for a vertical equation. Visual CAD maintains the VPI order that you define. Both of these VPI s should have zero or blank vertical curve lengths. Defining VPI s From Existing Survey Points You can view the projection of 3D survey points on the profile grid with the View=>Profiles=>Points On Profile Sheet command. This projects each point selected onto the active alignment to calculate the profile grid station. Once a survey point is drawn on the profile grid, you can define a VPI that matches its station and elevation by clicking the SnapSPnt button and snapping to the point. Defining VPI s From Terrain Profile Points There are two ways you can define VPI s to match points on a stored terrain profile. The first is to click the MergeTerrainProf button. This allows you select a terrain profile file (.pf$), then select the beginning and ending station from the terrain profile to merge. The station and elevation of every point in the specified station range is loaded into the spreadsheet as a VPI. If you just want to tie to a single point on the terrain profile, you can use the SnapTPnt button. This lets you snap to a point on the terrain profile, then defines a VPI with a matching station and elevation. Defining VPI s from a Survey Chain You can also use points on a survey chain to create profile VPI s. Select the Geometry=>Profiles=>Store/Edit command and click the Merge Survey Chain button. The Merge Survey Chain to Design Profile dialog box will be displayed, as shown below. Connecting Profile Builder The purpose of this macro is to create and store a profile for the chain that connects the edge of travel way of a main road to the edge of travel way of an intersecting or crossing road. (Note - the edge of travel way (ETW) does not include the shoulder. It should not be confused with the edge of pavement). The components and layout of the connecting profile are shown in the diagram below. 11

12 SETUP PAGE To define the profile, you must first establish the name of the connecting geometry chain, and the Begin and End points. The Begin and End points define the stations and elevations where the profile begins and ends.the begin and end stations are not necessarily the beginning and end of the connecting chain, which may extend well beyond the limits of the intersection. The Begin Point can be defined by establishing a position using any of the Position Picker options, such as snapping to an existing point, locating along an object, or giving a station and offset. The selected position is projected onto the Connecting Chain to calculate and display the station. If possible, the Position Picker will also automatically set the Elevation of the Begin Point. For example, if you use the position picker to snap to a point with a defined elevation, that elevation is automatically placed in the Elevation field. You can also set the Elevation of the Begin Point directly by entering elevation values, or by using the elevation picker controls. Setting the End Point works exactly as described above for setting the Begin Point. 12

13 PROFILE COMPUTATION PAGE To calculate the profile it is necessary to establish the grades at the beginning and end. These items are defined on the Profile Computation page. It also provides controls to define the location of the low point. Set Grade At Begin Point To set the grade at the Begin Point you must specify a point and elevation on the back grade of the profile. This point is referred to as the Back Point. The grade back is calculated as gb = (Begin Point Elevation Back Point Elevation) / (Begin Point Station Back Point Station) If the Point Back position does not project onto the connecting chain, its station is calculated by subtracting its distance from the beginning of the chain from the initial station. The station of the Point Back and the computed grade are displayed on the dialog box. Set Grade at End Point To set the grade at the End Point you must specify a point and elevation on the ahead grade of the profile. This point is referred to as the Ahead Point. 13

14 The grade ahead is calculated as gb = (Ahead Point Elevation End Point Elevation) / (Ahead Point Station End Point Station) Low Point Options Before computing the profile, select a Low Point Option so that the profile PI will be shifted to prevent the low point of the vertical curve from occurring along the curve of the connecting chain. If the Do Not Move option is selected, then no adjustment is attempted. If the Move to PC/BC option is selected, and the low point lies along the curve of the connecting chain, the PI station is shifted toward the PC until the calculated low point is no longer on the curve. If the Move to PT/EC option is selected, then the PI station is shifted toward the PT until the calculated low point is no longer on the curve. PREVIEW PARAMETERS PAGE The Preview Parameters page of the dialog box sets the parameters needed to Preview the connecting profile graphically. This is similar to setting up Profile Sheet Format Settings in CAiCE, except that the parameters are not saved permanently. To preview the profile you must define the following items: 14

15 Other Geometric Layout Commands Best Fit Alignment Best Fit Profile Compute Street Intersection Offset Chains Store Offset Parallel Chains 15