A demand segment is a demand group or class, which is allocated in one step to a network, because the demand is homogeneous to the group. Examples for a demand segment could be pupils or commuters. The journey times from origin zones to destination zones are calculated per demand segment (Demand segments).
Demand segments are different from demand strata (Demand strata). Demand strata contain demand groups for the steps trip generation, trip distribution and mode choice of the Standard 4-step model. Another important difference is that each demand segment is assigned to exactly one mode (for example PrT or PuT).
The demand strata of a mode are generally aggregated to create demand segments. These aggregated demand segments are then assigned to the network. Aggregation is possible since the variables used to differentiate between the demand strata have no effect on the assignment. Demand strata, for instance, are often distinguished by employment, e.g. employees with a car and non-employees with a car. If the study area has no toll roads, the employee status plays no role for route choice during the assignment. In other words: Everyone chooses the same route between the origin and destination zone, irrespective of their income level. So demand strata can be aggregated to a demand segment for assignment.
To calculate an assignment, the system needs to assign each demand segment exactly one matrix (Matrices). For dynamic PrT assignments and all PuT assignments, a demand time series must also be assigned to each demand segment (Time series). Visum establishes the link between demand and transport supply.
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Notes: A possibly specified time series is ignored in the case of static PrT assignments. A matrix can also be assigned to several demand segments. The same applies to time series. |
