VISSIM 5.30-05 User Manual

6 The Traffic Network
- starting time [s]
► Every further row contains one value:
- Speed [m/s] at the end of simulation time step
The difference from the speed at the end of the previous time step
returns the constant acceleration (if positive) respectively
deceleration (if negative) during the current time step.
Every time step of the simulation the next speed information for each vehicle
will be read out of the file and assigned to that vehicle.
The new coordinate is determined by the equation of motion:
new_coordinate = old coordinate
+ old_speed ● time_step_length
+ 0.5 ● acceleration ● time_step_length 2
Example
If the parameter Simulation resolution is set to 10 Time steps per
simulation second, VISSIM will read ten speed time steps per second
from file.
This leads to a coordinate time step (time_step_length) = 0.1 seconds.
As soon as the end of the file is reached, the vehicle will be taken out of the
network.
6.4.3 Vehicle Inputs (Traffic Volumes)
In VISSIM, time variable traffic volumes to enter the network can be defined.
For vehicle input definition, at least one vehicle composition has to be
defined, cf. section 6.4.1.
Traffic volumes are defined for each link and each time interval in vehicles
per hour even if the time intervals are different from one hour. Within a time
interval vehicles enter the link according to a Poisson distribution.
If the defined traffic volume exceeds the link capacity the vehicles are
‘stacked’ outside the network until space is available again. If any ‘stacked’
vehicles cannot enter the network within the defined time interval, a message
is traced to a log file (same name as input file with extension *.ERR)
indicating also the time interval of the particular input. Furthermore, the user
is notified in detail at the end of the simulation. Please note that if the vehicle
input time interval exceeded the simulation period, no messages are stored
in the *.ERR file in case there are stacked vehicles left. The maximum
volume that can be reached depends on permitted speed and driving
behavior parameters.
Input flows do not need to be defined when Dynamic Assignment is used as
then the flow data is contained in the OD matrices.
210 VISSIM 5.30-05 © PTV AG 2011