The core of the demand procedure is the definition of the utility and impedance parameters.
The impedance parameters of the shortest path searches (see Shortest path searches tab) refer to shortest path searches between locations. Strictly speaking, the shortest paths are created between the nearest active nodes. In the case of a private transport mode, any attribute of the shortest path can be selected. This refers to attributes that exist in common for links, turns, and main turns, and possibly also for restricted traffic areas. Since the attribute selection window refers to the link interface, not all displayed attributes are always selectable. If a dynamic attribute is to be selected, it must be a user-defined attribute.
In the case of a public transport mode, a matrix (at the level of stop areas) is specified instead of an attribute. Dynamic matrices are referenced by the matrix conditions [FromTime]=Context[FromTime] and [ToTime]=Context[To Time]. The impedance of the walk paths to and from the first or last stop area is defined at the top of the Shortest path searches tab. The maximum origin and destination walk time defined in the same place refers to each of the two walk links.
If there is more than one demand segment for a public transport mode, one of them must be selected for each tour group. A trip then receives this demand segment if the appropriate mode is chosen.
The impedance of a shortest path search is not automatically included in the utility calculation. With the definition of the shortest path impedance, only the shortest path itself is defined, not the utility. Attributes of the shortest path that are to enter in the utility are defined on the Base utility tab. For example, the impedance could be a weighted sum of travel time and costs, while in the utility travel time and costs are treated separately (e.g. to assign an individual time value to costs).
The base utility (see tab Base utility) is composed additively of several components, each of which is defined in a row. A row consists of four columns:
- Activity execution factor
- Zone utility
- Location utility
- Impedance attribute for shortest PrT path or impedance matrix for shortest PuT path
The activity execution factor is a formula of the activity execution interface. Thus, all attributes of the activity execution as well as all derived attributes can be used for the utility definition. For example, individual utility components can be defined that are only effective for work paths. Time-dependent attributes must not be used.
The activity execution factor is evaluated at the beginning of the calculation. This means that in particular those attributes and derived attributes are not available that are determined during the procedure. This includes the location and some From-trip and To-trip attributes. Although these attributes could be used technically, they may not be used.
The zone utility is a common matrix formula. In addition to matrices, zone, network, and mode attributes can also be used via the CONTEXT operator. In the selection window, other relations such as those to the person group are offered, but you must not select these. Dynamic matrices are referenced by the matrix conditions [FromTime]=Context[FromTime] and [ToTime]=Context[To Time]. Other dynamic attributes cannot be used.
Location utility refers to the shortest path between each two locations. It replaces the matrix utility common in aggregate models. In the case of a private transport mode, any attribute of the shortest path can be selected. This refers to attributes that exist either jointly for links, turns, and main turns, or exclusively for restricted traffic areas. Since the attributes selection window refers to the link interface, not all displayed attributes are selectable. Attributes of restricted traffic areas cannot be selected from the attribute selection window, they must be entered manually. If a dynamic attribute is to be selected, it must be a user-defined attribute.
In the case of a public transport mode, an impedance matrix (at the level of stop areas) is specified instead of an attribute. Dynamic output matrices are referenced using the context operator, as with the zone utility.
In addition to the impedance matrix, the walk path time can also be selected as the location utility. It includes the walk path time to the origin boarding point (in the first stop area) and from the destination boarding point (from the last stop area). It is determined based on a shortest path in the public transport walk network between the stop area and the location.
The walk path time is used to represent a household's individual connection to public transport. This is one of the key skims that determine individual public transport use but is usually only modeled in a very simplified way in aggregated models.
