From the limited number of rental vehicles and the constant capacity of car sharing stations as well as from dynamic demand, it may be concluded that the impedance to using sharing systems depends on their capacity. The impedances are calculated per time interval. The Interval length within an assignment period is an input variable.
- Impedance for renting from a station or a zone
- Impedance for returning a vehicle to a station
- Initial vol/cap ratio during first connection search
Impedance for renting from a station or a zone
For station-bound systems, the vol/cap ratio-dependent penalty term is used to model booking situations at a station where you first have to wait for a vehicle to be returned by the renter or operator. For non-station-bound sharing systems, it is used to model situations in which the average path length to a parked vehicle becomes longer, the smaller the “vehicle density” in the environment is.
The malus of a path leg is calculated based on the following components:
- V = vehicles available for the path leg of the selected TSys, i.e. the number of vehicles at the beginning of the interval, minus the number of vehicles already rented (during the previous interval). A rental vehicle parked in a zone only becomes available after the minimum dwell time saved for the zone has elapsed.
The additional impedance of a path leg is then calculated as follows
with the parametersc1,c2 andc3 entered by the user, where c3, in the case of renting from a station, is an attribute of sharing stations that allows the size of the area to be included. When renting at a zone, c3 is an attribute of the zone.
Impedance for returning a vehicle to a station
The supplement based on vol/cap ratio for the return at a station is used to model situations in which you might have to wait for a parking space to become available.
The malus of a path leg is calculated based on the following data:
- P = vehicles available at the station, i.e. the number of vehicles at the beginning of the interval, plus the number of vehicles already returned (during the previous interval).
- C = station capacity
The additional impedance of a path leg is then calculated as follows:
The user specifies the parameters c1 and c2.
The penalty term does not affect station-based systems or systems in which the return and rental station must be identical.
Balancing of dropped off and picked up vehicles at zones (destinations)
Within the analysis period, the number of dropped off and picked up vehicles at a zone (destination) should balance out. The balancing models the case where a vehicle can only be picked up after one has been dropped off. In a path-based transport model, the equivalent would be a user trip with a rental vehicle (rental -> path -> activity -> path -> return).
Paths that begin or end at a zone with the drop off or pick up of a rental vehicle are assigned a bonus or malus, depending on how this affects the balance. The term used for calculation includes the following:
- Sum of dropped off rental vehicles (zone is destination of path)
- Sum of picked up rental vehicles (zone is destination of path)
For paths that pick up the vehicle at the zone, the following is added to impedance:
I = a•(S2origin zone - S1origin zone)
where a is a parameter entered by the user.
For paths where the vehicle is kept, the following is added:
I = a•(S1destination zone - S2destination zone)
where a is the same parameter entered by the user.
Initial vol/cap ratio during first connection search
When performing their first connection search, users can choose a start solution that assesses the vol/cap ration of the sharing system. This Initial vol/cap ratio in percent ensures that the most realistic paths are found from the first search on, as a vol/cap-dependent search impedance is used for rentals from stations (Using Visum: Timetable-based assignment: Extended consideration transport supply page).
The impact of this start solution on the final result is considerably reduced if you perform a second search within the loaded network.
