Visibility Check - Check Intersection Sight Distance

Last updated: 2022-02-01

The tool checks the clear sight window for Intersection Sight Distance utilizing input options for decision point location, eye height, required sight distance, target vehicle path, and terrain surface. Obstruction surfaces can also be included as part of the sight analysis. The object height used along the target vehicle path is 3.5 feet above the terrain surface based on FDM 11-10-5.1.4.1 Clear Sight Windows.

WisDOT Design tab > Analyze panel > Visibility Check dropdown > Check Intersection Sight Distance

The tool can also be accessed from the command line: DOTCHECKISD.

Intersection Sight Distance Dialog box

  1. Sight Lines
    1. Decision Point
      1. Click button
      2. 'Pick decision point (eye) location:' snap to desired location
      3. Checkmark appears in the dialog box after successful selection
    2. Vehicle Path
      1. Click button
      2. 'Select target path (2D Polyline) in check direction:' select polyline
        1. Recommend using 2D polyline that is in the center of the lane
        2. Select the polyline on the side that vehicles are approaching from depending on which turning movement is being analyzed.
        3. Checkmark appears in the dialog box after successful selection
    3. Eye Height (at decision point - FDM 11-10-5.1.4.1 Clear Sight Windows)
      1. 3.5 feet (car)
      2. 7.6 feet (truck)
    4. Sight Distance
      1. Enter required sight distance based on FDM standards
        1. FDM 11-10-5.1.4 Intersection Sight Distances (ISDs), Vision Triangles, and Vision Corners)
        2. FDM 11-10 Design Controls, Table 5.2 Intersection Sight Distance Criteria...
  2. Surfaces
    1. Terrain Surface - Ground surface that will be evaluated
      1. For proposed designs, it is recommend that a Cmbn-Ex-Top surface is created (a combination of the refinement Top surface with the existing ground surface) for this analysis.
    2. Obstruction Surfaces
      1. Select surface(s)
      2. Multiple surfaces can be selected by using the Ctrl-click for individual surfaces within the list or Shift-click for a range of surfaces that are consecutive in the list of surfaces.
      3. Use Ctrl-click to deselect an obstruction surface.
      4. See Create Wall Surface for additional information.

  3. OK

Three dimensional lines are created from the decision point to 1-foot increments along the target vehicle path or the intercepting obstruction.

Green lines = clear sight line

Red lines = obstructed sight line

An Mtext label is placed at the last sight line prior to an obstructed sight line, indicating the available sight distance.

Each sight line is an AutoCAD Line object. All of the sight lines are combined into an AutoCAD Group object. This allows for the selection of all the sight lines in order to delete, hide or isolate them at the same time, while still maintaining the flexibility of layer control on the lines.

If an individual element within the group requires a manual edit, set the PICKSTYLE variable to 0. This makes each element in the group selectable. When editing is complete, set the PICKSTYLE variable back to 1.

The tool creates the following layers (based on input parameters). If the layer already exists, then that layer will be used.

  • P_SIGHT_Text
  • SIGHT_ISD_L_ObstructedSightLines_3.5ft_EyeHt
  • SIGHT_ISD_L_ObstructedSightLines_7.6ft_EyeHt
  • SIGHT_ISD_L_VisibleSightLines_3.5ft_EyeHt
  • SIGHT_ISD_L_VisibleSightLines_7.6ft_EyeHt
  • SIGHT_ISD_R_ObstructedSightLines_3.5ft_EyeHt
  • SIGHT_ISD_R_ObstructedSightLines_7.6ft_EyeHt
  • SIGHT_ISD_R_VisibleSightLines_3.5ft_EyeHt
  • SIGHT_ISD_R_VisibleSightLines_7.6ft_EyeHt