# Horizontal Parameters

To enter geometry data relating to the horizontal alignment, click the Horizontal tab. Horizontal geometry data is divided into three groups; Curves, Transitions, and Straights.

## Curves

Specify the following in the Horizontal tab:

Minimum horizontal radius of curvature (H Rad)

Superelevation on minimum radius curves (Super)

Stiffness

## Minimum horizontal radius of curvature (H Rad)

The minimum horizontal radius that you enter will be determined by terrain, design speed, and the purpose of the road or rail. The value you enter could determine how closely the alignment follows the natural surface and as a result can affect the amount of earthworks required.

Superelevation on minimum radius curves (Super)

If a curve has a radius larger than the minimum radius specified the superelevation applied to the curve is inversely proportional to the ratio of the radius of curvature to the minimum radius: a curve with a radius of curvature double the minimum radius will have half the superelevation, and a straight will have no superelevation.

## Stiffness

Stiffness affects the number of curves and the rate of change of curvature in generated alignments. When the stiffness parameters are close to 0, the alignments follow the natural surface as closely as the geometric standards permit; when the stiffness parameters are close to 1, the alignments minimize changes in curvature at the expense of higher construction costs. The selection of the appropriate stiffness is empirical, and a good starting point is to assign the value of 0.5 to these and then experiment.

## Transition

In Quantm Desktop software, you can convert an alignment from a curvilinear alignment (defined by a 3d spline of constantly changing radii) into a geometric alignment (with straights, curves, and transition curves, etc). The transition parameters are used during this conversion process. For more information on converting alignments, see Manually Editing Alignments.

Specify the following in the Transition group:

Transition Type

Length Convention

Transition Length or Transition Length at minimum radius

## Transition Type

Specify the type of transition curve. If there is no transition required, select None, the converted alignment will consist of straights and circular curves.

## Length Convention

In the Length Convention box, specify the method you want to use to determine the transition length. Either select a fixed length for all transitions (eg all are 200m) or have the length vary linearly based on a ratio of the radius at a point to the minimum horizontal radius specified in the curves group. For example, if the minimum H radius is 1000m and the transition length at min radius is 100m, then a 2000m radius curve will have a 50m transition, and a 4000m radius curve will have a 25m transition. The Transition group will vary depending on the length convention selected.

## Transition Length

If the Length convention selected is fixed, enter the transition length you would like to use. If linear is selected, enter the transition length to use when the radius is the minimum specified. If the radius is larger than the minimum, the transition length will be calculated.

Note: If the transition length specified is too large to enable the generated geometric alignment to be a 'best fit' of the curvilinear alignment,Â Quantm Desktop software will use the largest possible transition length.

## Straights

These settings are used for generating warnings. They have no effect on the generated alignment.

Specify the following in the straights group:

Horizontal Minimum

Back-to-Back (horizontal)

## Horizontal Minimum

Straights are measured from the end of the transition curve (or circular curve if there is no transition) to the start of the next transition curve (or circular curve). If the straight is less than the Horizontal minimum a warning will appear.

## Back-to-Back (horizontal)

Check Back-to-Back if you want to ignore small straights and allow back-to-back curves in the same direction or in the reverse direction.

Next topic: Vertical Parameters