Structure Gauge and Kinematic Envelope
To ensure that the path required for the passage of trains is kept clear along the route of a railway, a “structure gauge” is imposed. This has the effect of forming a limit of building inside which no structures may intrude. The limit includes not only things like walls, bridge sand columns but also pipes, cables, brackets and signal posts. The structure gauge will vary with curvature of the line and maximum speeds allowed along the section in question. Just as the civil engineer is prevented from allowing his structure to intrude into the train path, the rolling stock engineer also has limits imposed on the space his train may occupy. This space is referred to as the “kinematic envelope“. The area designates the limits within which the train can move laterally and vertically along the route. Speed and features of train design such as bogie suspension and special systems such as tilting that it may have will affect the kinematic envelope.
The line route has to be checked from time to time to ensure that the structures are not interfering with the gauge. A line is always gauged when a new type of rolling stock is to be introduced. It is important to see that small variations in track position, platform edge, cable duct location and signal equipment haven’t been allowed to creep inwards during maintenance and renewal programmes.
The Kinematic Envelope is the envelope of the tram as it travels at constant speed along a straight and level track.