Users of infrastructure for private transport are mostly car drivers and their passengers, but also non-motorized travelers such as cyclists and pedestrians. Users of public transport are public transport passengers. Objective of the user model is to determine the impacts of a transport supply system on travelers. Important skim data for evaluating the transport supply are the journey time and traveling expenses between two zones. To evaluate a public transport supply, additional skim data such as number of transfers, transfer wait time and service frequency must be considered.
To determine these user-specific skims, the OD trips of travelers are modeled. A user chooses a route for his trip which appears convenient to him. If in addition to the route, the user also selects the departure time of his trip, one speaks of a connection independent of the mode. In addition to the spatial course, a connection thus comprises the entire temporal course: In public transport especially the departure and arrival times at the boarding stop, at the transfer stops and at the destination stop and in private transport the selected departure time, the arrival time and the transit time for each location along the route. If the temporal progression of the traffic situation has been explicitly modeled in this way, one speaks of a dynamic model (dynamic assignment). There is no time axis for a static model, however, so that OD trips take place without temporal course and have a simultaneous effect on each location in the network. There are static and dynamic user impact models in both PrT and PuT.
Methods to model the travel behavior are based upon search algorithms which determine routes or connections between an origin and a destination. Procedures used as search algorithms are those which determine the best, meaning those which determine paths with the lowest impedance or a set of sufficient paths. Impedance can consist of times, distances, and costs. Depending on the search algorithm used, the paths found represent routes or connections. The trips by OD pair are distributed among the paths found. This combination of path search and trip distribution is called assignment. Private transport assignment assigns vehicle trips; public transport assignment assigns passenger trips.
For every route or connection between two zones skims can be calculated which describe the service quality of the route/connection. In addition to this, an assignment produces traffic volumes for links and turns, and in PuT projects also for stops and stop points plus all objects of the PuT line hierarchy from the transport system down to the level of individual vehicle journeys. In contrast to a quality skim such as, for example, journey time, the volume is only an indirect skim which by itself is not suited for evaluating the transport supply system. The volume is rather used to deduce
- saturation of PuT lines which affects the comfort of passengers and the revenues of operators
- noise and pollution emissions which indicate the environmental impact
Thus, the volume resulting from the user impact model serves as a basis for the procedures provided by the operator impact model and those of the environmental impact model as well.
Visum offers various assignment procedures for private and public transport. They differ by the search algorithm and by the procedure used for distributing demand. These assignment procedures are a central part of Visum. There are PrT models and PuT models.
- PrT (User model PrT)
- PuT (User model PuT)
