# Alignment element

Example: Curvature band right-hand curve with transition curve
Curve in road construction

Alignment elements (also known as design elements) are those mathematically defined sections through which the course of traffic routes such as roads , railway lines and shipping canals is planned and described in detail.

## Basics

In a narrower sense, the routing elements are straight lines , circles and transition curves , from which a route - the axis of a linear object - is composed horizontally. There are also elements for the vertical course, for example longitudinal slopes (gradients), cross slopes and their adaptation to the terrain .

Routing elements in the broadest sense are all variables that influence the routing, be they geometrical, structural or operational.

## Curves: arch shapes

The transition arcs are mostly clothoids , in railway construction also cubic parabolas , more rarely sinusoids . They are used for a constant, jerk-free change in curvature between straight and circular sections of the route or between flat and elevated sections. Hairpin bends and serpentines are mostly circular arcs with transition pieces. Curves that have a change in direction of less than 10 gon are called flat arches .

The jolt-free transition is not given with conventional routing. Elevation - ramp - and floor plan -  transition  arch - are laid out separately from each other. As a compromise solution, an attempt is then made to combine the two drafts.

Only by aligning the center of gravity , in which the center of gravity of the train or the respective wagon is guided through the arch with little force, is the requirement of smooth guidance almost fulfilled. In reality, this routing was already carried out as a Viennese arch on the Austrian Federal Railways and Wiener Linien. In both companies, the main alignment is now standard in the alignment regulations.

In addition to the Wiener Bogen there are forerunner projects such as the sine, cosine or the Blossrampe , which in reality were hardly ever implemented and are very difficult to manufacture.

## Route finding

The routing elements make it possible to optimize the route finding - between the most favorable adaptation to the terrain ( DGM ), good driving dynamics and the economic conditions. Technically, in addition to the short route v. a. to note:

• Limit values ​​for the gradient and curve radii of the route,
• low volumes of excavation and backfill as well as minimal difference between the two,
• minimal drainage and
• low impairment of neighbors and properties.

The planning variants are usually documented according to the kilometers along the route, but integrated into the coordinates of the national survey .

The size of the radii in the arches or the change in the transition arches (the radius changes over the length) and the minimum lengths of the elements are summarized in a set of rules in railway construction, the routing regulation . This is drawn up by the railway company and approved by the responsible authorities. The routing regulations also contain formulas for permissible speeds and errors in the track position . The routing elements themselves are then shown in the site plan . This is a projection of the route onto the horizontal plane. The longitudinal profile is the projection of the route onto a vertical plane, i.e. the elevation.

## literature

• Manfred Weigend: Routing and layout of the track plan (VDEI series of publications). DVV Media Group GmbH | Eurailpress, Hamburg 2004, ISBN 978-3-7771-0321-1