Configure AlignmentConfigure Alignment

This functionality is available with the Computations and Profiles & Design Modules. It is also available in LISCAD Lite.

Configures the system for constants used in the design of combined curves.

The settings affect the horizontal geometry of a combined curve when it is created to meet design speed criteria.

Altering these settings will change the design speed of previously created combined curves but not alter their horizontal geometry.

The Configure/Alignments command is selected from the Utilities task.

Configure Alignment dialog box

Item Used to
Road: Select this option if you are designing road alignments.
Railway: Select this option if you are designing railway alignments.
Velocity: Select the design speed units that you prefer to use when creating combined curves. This setting will also affect the centripetal acceleration units.
Spiral: Configure LISCAD to use either a Clothoid or Cubic Parabola type spiral.
Centripetal Acceleration: Enter the value for the rate of change in centripetal acceleration to be used by the system for combined curve design.
It is defined for a spiral as A=V³/LR
Where:
  • V = velocity
  • L = length
  • R = radius
Typical values that should be used are:
  • Less than 80 km/hr A = 0.60
    Between 80 and 120 km/hr A = 0.45
    Greater than 120 km/hr A = 0.30
The value must be within the range of:
  • 0.98 to 3.283 feet per second squared per second
  • 0.3 to 1.0 meters per second squared per second
Note: The units displayed for the centripetal acceleration will vary according to the velocity that is set.
Coefficient of Side Friction: Enter the value for coefficient of side friction to be used by the system for combined curve design (not applicable to railways).
Typical values that should be used are:
  • 0.40 at 30 km/hr
  • 0.19 at 110 km/hr
However, from a passenger comfort point of view, the design range is restricted to:
0.11 to 0.19.
Maximum Superelevation: Enter the value for maximum superelevation to be used by the system for combined curve design. The value must be within the range of:
0.0 to 10.0 percent
Station: Display alignment chainages in station format according to the value in the Spacing field. For example, when Station is selected, and the Spacing is set to 20, a chainage of 430.5 will be displayed as station 21+10.5 (21 * 20 + 10.5 = 430.5).
Spacing: Select the Station spacing.
This is only valid if the Station radio button is selected.
Chainage: Select that alignment chainages are not to be shown in station format.
Data Input By
Chainage: Select that the position along the alignment is entered as chainages.
Distance: Select that the position along the alignment is entered as distances.
Default: Restores the above three design values to typical values hard wired by the system.
System: Save the changes for use as default settings when a new project is created.