Concerning spatial road alignment the effective German guidelines are largely limited to qualitative statements and do not inherit sufficient procedures for representation and control. The field of spatial alignment (chapter 6 of RAS-L) is limited solely to perspective illustrations which can only be analysed subjectively. Therefore the objective of this paper is to lay down both a practicable method for representation and control as well as quantified criteria for the evaluation of spatial alignment. Starting from the physical field of optical perception the graphical and quantitative methods of evaluation as found in the literature are layed down. Special emphasis is put on the theoretical background and the discussion of the usefullness of the known methodes in rating changes of angle or visible radii in the perspective view of the driver. Following this evaluation criteria to describe the characteristic lacks of poor spatial alignment are derived from the phenomenons sight distance, partial road disappearance from driver's view (diving, jumping), sight distortion, sight quality and the sight on curvature changes. For the evaluation of the phenomenons of sight distances and partial road disappearences the depth of hidden roadway parts under the horizon will be inspected. Using a alignable definition for the sightmarks it is possible to restrict the so far two phenomenons stopping sight distance and overtaking sight distance to only one sight distance detection: The mark in the middle of the own lane up to 400 m (scope of the stopping sight distance) and from 400 m on in the middle of the lane of opposing traffic (scope of the overtaking sight distance). This model shows the sight beams according to the current model of stopping and overtaking sight distance in their perspective distance scopes. The evaluation of sight distortion and sight quality is based on the relation between the visible roadway surfaces of the genuine alignment and the corresponding horizontal alignment without influence of vertical alignment and crosafall. The derivation of the mentioned evaluation values from perspective data and their length referenced diagram is explained. The results are summarized in a diagram named "QuaSi-Band" - the course of sight quality - containing all influential evaluation criteria of spatial alignment. It shows the data of road disappearance depth and sight quality for each viewpoint along a given alignment. Examples for the evaluation of the quantitative criteria in length context including a differentiation of the known poor spatial alignment phenomena are shown. To help to avoid poor spatial alignments in the planning process fundamental quantified possibilities are named. They refer to covered curvature changings, diving and the application of cubic parabola as vertical curve. For typical lacks of planned alignments, which are detected by using the QuaSi-Band", a range of possible modifications is shown. Following this possibilities of detecting and minimizing risks on existing roads by using the QuaSi-Band are named. Selected examples of ,,QuaSi-Band" and belonging perspective views of an example alignment under different conditions are shown in the appendix. (Author/publisher)
Abstract