This option uses the "best" route search strategy on the basis of the particular time of departure and the time of arrival. A shortest-path algorithm based on this data calculates the best connection between two traffic zones for a particular departure time. For different times of departure, various "best" connections may be calculated which may differ by the used PuT lines and/or transfer stops. To determine all "best" connections within the analyzed time interval the shortest path algorithm is performed several times for all possible departure times within the analysis time interval.
Since in some cases several connections are possible for a given time of departure, a definition of "best connection" is required for these search procedures. For this purpose Visum provides an impedance function which increases the impedance of a connection for each transfer by the transfer penalty. A low penalty has the result that connections which take the least time are favored, while a high transfer penalty gives priority to connections with a lower number of transfers.
- Determination of all possible start times for trips which originate in traffic zone i. The start times result from the departure times of PuT lines at stops which can be reached from zone i via a connector.
In the example, the start times correspond with the departure times of bus line 1 from A-Village (6.10, 6.55, 7.25), because A-Village is only serviced by one bus line and an access time of 0 minutes is assumed.
For every start time one of the two following steps is executed.
- Either a monocriterion shortest path search is carried out which searches for the "best" path from traffic zone i to traffic zone j starting at the given time. The search procedure identifies the path with the lowest impedance as the best path. The impedance of the path is measured in minutes and is a linear combination of journey time and number of transfers. It consists of the following time components.
- Access time [min]
- In-vehicle time [min],
- Transfer walk time between two transfer stops [min],
- Transfer wait time [min]
- Egress time [min]
- Number of transfers [-] • transfer penalty [min] (adjustable).
This lowest impedance path represents a connection, because the used sequence of lines and the exact departure and arrival times at boarding stop, transfer stops, and alighting stop are known.
- Or the connection with the minimum journey time (so-called bicriterion shortest path search) is calculated for each permitted number of transfers (for all integer values ≥ 0 and ≤ max. number of transfers). If the calculation returns identical journey times for different numbers of transfers, the program only stores the connection with the lowest number of transfers (dominance).
