Unit 5 – Lesson 1: Roadway Alignments Civil 3D 2010 Student Workbook ▪ 1 Roadway Alignments Overview In this lesson, you learn how to work with alignments specifically intended for transportation projects. These are typically more advanced designs than those used for subdivision design. Alignments are frequently criteria-based and may include superelevation and offset alignments. When engineers plan and design transportation facilities for both new construction and road reconstruction projects, they must create and then edit the alignments used to control the design of the road. You create tangent, curve, and spiral alignment components with layout tools, and you can edit alignments both graphically and in a table. When you edit alignment data in a table, the graphical display of the geometry and associated annotation is automatically updated. When you edit alignment data graphically, curves maintain tangency to the lines. When you edit alignment geometry, surface profile data also automatically updates. The following illustration shows two intersecting alignments: Lesson 1 AutoCAD Civil 3D 2010 Education Curriculum Student Workbook Unit 5: Transportation DesignUnit 5 – Lesson 1: Roadway Alignments Civil 3D 2010 Student Workbook ▪ 2 Superelevation is the purposeful canting of road or railway cross sections within spiral and curve alignment components. The intent is to counteract centrifugal forces to allow for higher design speeds and safer passage through alignment spirals and curves. To calculate superelevation values for an alignment, you modify alignment properties to assign a design speed. The superelevation values are referenced from a rate table in a design criteria file. Each curve is a superelevation region, and for each superelevation region, you can assign independent superelevation properties. You can also apply the superelevation properties of one superelevation region to the other superelevation regions in the alignment. When you use alignment design criteria and superelevation, you associate standard imperial and metric superelevation tables with the alignment to calculate minimum curve radii and superelevation critical values for assigned design speeds. The superelevation values assigned to an alignment are referenced when you create the corridor model for the transportation facility. Offset alignments are directly related to the centerline alignment. When you change the geometry of the centerline alignment, the geometry of the offset alignment automatically recalculates based on the offset parameters.Unit 5 – Lesson 1: Roadway Alignments Civil 3D 2010 Student Workbook ▪ 3 Objectives After completing this lesson, you will be able to: - Describe alignments and their properties. - Create alignments using objects. - Describe alignment tag labels. - Label alignments and create a table. - Explain criteria-based design. - Create alignments using layout tools. - Calculate and apply superelevation to a horizontal alignment. - Create offset alignments and widenings. Exercises The following exercises are provided in a step by step format in this lesson: 1. Create an Alignment Using Objects 2. Label an Alignment 3. Create an Alignment Using Layout Tools 4. Edit an Alignment 5. Apply Superelevation 6. Create Offset Alignments and Widenings About Alignments An alignment is a series of coordinates, lines, curves, or spirals used to represent linear features such as the centerline of a road, edges of pavement, sidewalks, and rights-of-way. Creating and defining the alignment is one of the first steps in a transportation design project. The alignment controls the horizontal location of a transportation corridor model. The alignment serves as the controlling geometry for the layout and construction of the road. Detailing the particular geometric points of alignments is critical in order for the design engineer to provide clear communication of the engineering data for the client, reviewers, and contractors. Alignment labels and styles are effective tools for providing this communication. Alignments are the first of the three primary design planes to be laid out and used by the designer. Profiles and cross sections provide the other two design planes necessary for a full three-dimensional description and modeling of proposed roadways.Unit 5 – Lesson 1: Roadway Alignments Civil 3D 2010 Student Workbook ▪ 4 Alignment Subentities Alignments are created and displayed with subentities. The alignment components are lines, curves, spirals, arrows, line extensions, and curve extensions. Alignment lines, curves, and spirals can be either fixed, floating, or free. Fixed, floating, and free entities are summarized in the following table. Term Description Fixed Entities Alignment lines, curves, and spirals can be fixed entities. Fixed entities have a fixed position and are not necessarily tangent to another entity for the definition of its geometry. Floating Entities Alignment lines, curves, and spirals can be floating entities. When a floating entity is created, it is tangent to one other alignment entity for the definition of its geometry. Free Entities Alignment lines, curves, and spirals can be free entities. When a free entity is created, it is tangent to two other alignment entities for the definition of its geometry. An alignment segment with a generated curve is shown in the following illustration. Keep the following guidelines in mind when you create alignments: When you create an alignment from a polyline with no curves, or from lines, you can automatically add curves between the tangents. You can assign a value to the starting station of the alignment, which is the start point of the polyline, line, or arc. Alignment station reference points and base stationing values can be adjusted later. Alignments can either be independent or included in a site. Use alignments in a site if you want them to interact with other objects in the site, or if you want to use sites to organize the alignments.Unit 5 – Lesson 1: Roadway Alignments Civil 3D 2010 Student Workbook ▪ 5 Labeling Alignments Horizontal alignments are made up of segments, which are lines, arcs, or spirals. There are a number of powerful labeling tools in AutoCAD® Civil 3D® software for labeling horizontal alignment geometry, either on the alignment itself or in a table. When you edit or change an alignment, associated labels
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