Creating a Railway Surface

You can design a railway surface by setting up track width, railway surface offset, sleeper length, left/right ballast shoulder width (fixed or as laws), rotation mode and cant (as laws). Unlike road design, there is no normal slope applied to the railway surface, the drainage being done through the ballast.

You can design a railway surface with transitions to attain superelevation in turns. The transition lengths as well as the superelevation value are functions of design speed, alignment geometry and standards. Key points/alignment points contain speed and minimum superelevation information (angle) used for design rules. The railway surface is based on a sweep, the angle and width of which are driven by rules/laws.

Superelevation tilts the railway to help offset centrifugal forces that develop as the train goes around a curve, and they are what keep the train from going off the rails. It helps a train steer along a curve, keeping the wheel flanges from touching the rails, minimizing friction and wear resistance. Superelevation values are determined by country regulations and they depend on superelevation rate and curve radius.

See Also
About Rotation Modes on a Road/Railway Surface
  1. From the Railway section of the action bar, click Horizontal Alignment .

    For more information about the alignment options, see Creating an Horizontal Alignment.

    You switch into the Alignment Sketcher app. The Horizontal alignment initialization dialog box opens:

  2. Choose a profile (railway machines): Streetcar, Inter-city or High speed, because some parameters (design/maximum speed and curve gradient) may be different depending on the model selected.

    Profiles are based on the existing xml file of Data Setup called RailwayAlignmentDesign. The corresponding parameters and rules are displayed in the lower part of the window. They correspond to the selected profiles, managed in Data Setup. You cannot edit them.

    Profiles are managed in Data Setup. It is compulsory to select a profile to validate the surface creation. Without selection, the OK button is disabled.

    The selected label (context) appears highlighted as blue.
  3. Click OK.
    A panel is docked and contains three tabs: the Alignment assistant, the Stationings and the Specifications of the railway project. The panel can also be floated to one of the four sides of the 3D area, or snapped to other panels. The Specifications tab contains the parameters and rules corresponding to the selected profile. These editable values correspond to the values set on the alignment start point.
  4. Choose key parameters and rules that should apply to the future railway alignment.

    Values are editable and correspond to the values set on the alignment start point. Only specifications that can be overloaded are displayed.

    Default design rules (Railway Radius Rule, Railway Length Rule, Railway Gradient Rule and Railway Superelevation Rule) are provided by default but you can choose others in an XML document (in Design Rules from Data Setup).

  5. To create your profile with points, lines and arcs, click Alignment Profile .

    Design checks are run when designing horizontal and vertical alignments. They are based on design rules. In the Alignment assistant, check if the radius is compliant with the rules of the selected machine. For more information, see Creating a Horizontal Alignment.

    Road and railway alignments are stored in the same Alignment set. Road and railway surfaces are stored in nodes, at the level of the Alignment set.

  6. To change the superelevation value, double-click an horizontal alignment in the tree.
    You switch into the Alignment Sketcher app. The Alignment assistant panel appears.
  7. Double-click a key point.
    The Alignment point dialog box is displayed. It is split into two sections:
    • Parameters: used to create the horizontal alignment. See Creating an Horizontal Alignment.
    • Design Rules: predefined status have already been defined (for radius, length, gradient and superelevation) in design rules which are a series of recommended parameters to check the correctness of transition formulas.
  8. To edit the superelevation rate, do either of the following:
    • Under the Parameters section, use the combo box of Superelevation to edit the rate of the maximum slope in the following road turns (5% for example). The slope angle on the selected alignment point is not modified, next alignment points inherit from the current rate and the Superelevation field is renamed into Current superelevation containing the inherited rate.

      To modify the superelevation value again, click Edit next to Current Superelevation.

    • Under the Design Rules section, use the combo boxes to edit the superelevation tables/laws (defined in Design Rules in Data Setup) used to connect transition sections with different superelevation rates. For more information about design rules/tables, see Building and Civil Resources in the Data Setup User's Guide.

      When no superelevation value has been set, the current value displays the information of the previous alignment points.

      Design Rules can be selected in session. They allow to define several horizontal radius tables depending on a superelevation rate. For example, you can add curve radius rules according to the speed.

  9. To create a vertical alignment, click from the Alignment assistant.
    For more information, see Creating a Vertical Alignment.
  10. To create a 3D alignment, click from the Alignment assistant.
    You switch into the Civil Engineering 3D Design app. For more information, see Creating a 3D Alignment.
  11. To display alignment segment information, click from the Railway section of the action bar and select an alignment point.
    An Alignment segment information window appears. You can read information about the start/end point position, elevation, start direction and segment length.
  12. Export alignment information in a report to the format of your choice by clicking Export Alignment Report from the Railway section of the action bar.
  13. To create a railway surface, select a 3D Alignment in the tree or in the 3D area.
  14. From the Railway section of the action bar, click Railway Surface .
    The Railway Surface dialog box is displayed:
    • The Alignment box is filled with the selected item.
    • Select a Rotation axis:
      • Center line: The traveled way revolves about the centerline.
      • Inner rail: The traveled way revolves about the inside turn.
      • Outer rail: The traveled way revolves about the outside turn.
    • Select a superelevation Mode:
      • Automatic: you can specify the transition rate which the percentage of the maximum cant in turn achieved at the beginning of the arc section (basic mode). Transition computation based on Design Rules from Data Setup that control runout/runoff lengths based on speed, curve radius, superelevation and transition rates. A law/sketch is created, and the slope percentage is applied point by point. See information about Parameters section below.
      • By law: transition sections have a representation that you can modify. When you select this mode, other options appear: See the step 11.
    • Select:
      • The Transition rate: the fractional part of transition length (from Design Rule table) achieved before curve point, it starts on the straight path and end at the beginning of the curve (at 100%). This option can only be used when the Automatic mode is selected. It should be used in a Business Rule to compute attainment methods. If 100% is chosen, it means that the Full Superelevation section will start precisely on an arc start point. You can choose a smaller value for the transition if you want it to finish within the curve, or choose a higher value if you want it to finish before the curve.
      • Smoothing: to introduce curve smoothing on transitions (where the maximum superelevation starts and ends). You can select this option only when the Automatic mode is selected. You can apply a smoothing to the law so that the change from straight line to superelevation is smooth.

        If you select By Law, the Transition rate and Smoothing options are hidden and appears on the right to edit the associated sketch.

    • Specify some parameters for the Vertical offset from rail top (a) and the Left/Right shoulder width (b/c):

      When you click one of the three boxes, this diagram appears:

      It displays the offset option (a) which is the vertical distance between the top rail and the surface to be generated. Shoulders options (b or c) are the distances between the sleeper end and the left/right ballast shoulder width.

      Select a shoulder option and type a width value to obtain a constant width. Or uncheck this option and click next to the shoulder option to define length by a variation law along the alignment. You switch into the Alignment Sketcher app.

      Notes:

      Only one superelevation rate (one side of the alignment) is supported for railways.

      Superelevation and transition lengths have been defined in cant tables (design tables provided by default), available in an XML document (in Design Rules from Data Setup, you can choose the RailwayAlignmentDesignRules_Default.xml). There is also a script allowing you compute the transition sections, to manage the transition/distribution of the lengths along the tangent and curve (runoff/runout). You can also customise these tables in Data Setup.