Empty trips are used for interlining a vehicle if the end stop point of the vehicle journey section to be carried out does not correspond with the start stop point of the vehicle journey section following in the block. The generation of empty trips is carried out according to the same principles, in the check line block and in both procedures of line blocking, and has direct effect on the data model.
The generation of empty trips via the attribute Create empty trips can basically be deactivated at the block version. Line blockings for this block version, as well as the check line block for line blocks in this block version, can therefore not calculate empty trips. If end and start stop point of consecutive block items do not correspond with each other, this is characterized as a location break.
If the generation of empty trips is generally allowed, Visum tries calculating an empty trip to change of location. This is always done relating to the empty trip transport system of the block. For a line block check, it is the specified empty trip transport system (input attribute). No blocks exist a priori for line blocking. Dependent on the parameter settings for each configuration (Partitioning) of a block which could occur, an empty trip transport system is predefined and saved to the actual generated blocks. This ensures, that with a later check the same empty trip transport system is used.
With the block version attribute Use system routes it can be specified further, how the empty trip calculation should be carried out:
- Do not use system routes
Empty trips are generated through shortest path search for the empty trip transport system in the network. The shortest paths in terms of distance or run time (t_PuTSys) are calculated, for example.
- Use system routes
If there is a system route for the empty trip transport system, from the origin to the destination point, the lengths and run time are applied as values for the empty trip. If there are specific run times for vehicle combinations, these have priority. The empty trip block item being generated has a relation to the system route used. System routes are not used transitive. If there is no suitable system route, a shortest path search is carried out in the network.
- Use system routes exclusively
The possible empty trips are solely described through system routes, a shortest path search is not carried out. If there is no suitable system route for an OD pair, interlining is not possible.
- Create system routes if required
Actually, the computation rules for the 'Use system routes' option apply. If no matching system route can be found for an empty trip, the successful shortest path search will create a new system route for this pair of stop points. The empty trip will use this information. The resulting 'empty trip' block item has a relation to the generated system route.
With the selection of the suitable option, the generated empty trips can be controlled in detail.
