| StartTag | S | Tag to annotate the start point of the alignment segment. | Text | 
| EndTag | E | Tag to annotate the end point of the alignment segment. | Text | 
| Start | S | The start point of the segment defined by a Cartesian point. | Point | 
| StartDirection | D | The direction of the tangent at the start point. Direction value 0. indicates a curve with a start tangent along the positive x-axis. | Number | 
| StartRadiusOfCurvature | R | For a NONLINEAR horizontal segment type the radius of the curve at the start point | Number | 
| EndRadiusOfCurvature | R | EndRadiusOfCurvature | Number | 
| SegmentLength | S | Segment Length | Number | 
| GravityCenterLineHeight | H | Optional attribute require for the exchange of Vienna bend transition segment. | Number | 
| PredefinedType | P | Predefined type of the horizontal alignmnent segment. | Text |