Modeling traffic demand with trip chain files
In addition to origin-destination matrices, the traffic demand can also exist in trip chain files *.fkt for dynamic assignment. A trip chain is defined as a result of a trip. In contrast to origin-destination matrices, a trip chain file delivers detailed data regarding trips of individual vehicles for the simulation. Therefore the generation of trip chain files is more complex compared to that of origin-destination matrices (Modeling traffic demand with origin-destination matrices).
Trip chains are only used internally in Vissim. Trip chains are generated from origin-destination matrices. Therefore demand data in the form of origin-destination matrices and trip chains can be combined for a simulation run.
Trip chain files do not take toll routes into account. Managed Lanes Routing Decisions affect the vehicles following a trip chain.
Content of the trip chain file
A trip chain file contains information regarding trips per vehicle (trip chain).
A trip chain is made up of one or more trips. A trip chain is allocated a vehicle and is defined by the following:
- Number of the vehicle
- Type of the vehicle
- Number of the origin zone
One or more trips result from the number and the type. A trip is defined by a group of numbers: four numbers for the data format 1.1. or five numbers for the data format 2.1:
- Departure time
- Number of the destination zone
- World coordinates of the destination (only for format version 2.1)
- Number of the activity
- Minimum dwell time
The departure time of the next trip is calculated from the arrival time in the zone and the minimum dwell time for the activity. The specified departure time of the next trip is only considered when the minimum dwell time is provided for: if the vehicle reaches the zone too late, the departure time is moved accordingly. The minimum dwell time is then added to the current arrival time.
Example trip chain file of a vehicle
07:00 departure from zone 1 (home)
to zone 2 (work)
dwell time 9 hours
17:45 departure from zone 2 (work)
to zone 3 (supermarket)
dwell time 30 minutes
6:30 PM departure from zone 3 (work)
to zone 1 (home)
dwell time 11 hours
