VISSIM 5.30-05 User Manual

12 Dynamic Assignment
2. Increase the demand gradually over the next iterations until the full
demand is reached. In order to conveniently control this process it is
possible to scale all OD matrices globally with a factor for the current
simulation. That factor can be set with the option Reduced Volume [%] in
the Dynamic Assignment window.
Using the VISSIM Batch Mode to Run Multiple Iterations
Since Dynamic Assignment normally requires many simulation iterations it is
possible to start VISSIM in batch mode and compute several subsequent
iterations without stopping. Therefore VISSIM can be called from the
command line with the –s parameter. The number n denotes the number
of iterations to be computed.
Example: VISSIM.EXE TEST.INP –S20
This entry would compute 20 iterations of the network file TEST.INP. This
feature can be combined with the congestion-avoiding scaling of travel
demand by using the command line option –v. The number p denotes the
percentage points by which the scaling factor in the input file is increased in
each iteration until 100% is reached.
Example: VISSIM.EXE TEST.INP –S20 –V5
This entry would compute 20 iterations of the network file TEST.INP and
increase the traffic demand by 5% in each iteration. E.g. if in TEST.INP a
reduced volume factor of 20% is defined then in the first iteration the travel
demand would be scaled down to 20%, in the second iteration increased by
5% from there (so there will be 25% of the full traffic demand), then 30% and
so on, and from the 17 th iteration onwards the total travel demand would be
assigned. Increased volumes will not exceed 100%. If 100% is reached,
further runs will also be performed with 100%.
Alternatively to option -s -v, the MULTIRUN functionality is provided in
the SIMULATION menu, cf. section 8.1.3.
12.8.3 Convergence Control
The process of iterated simulation runs to compute the result of the Dynamic
Assignment can be stopped if eventually a stable traffic situation is reached.
This is the case when travel times and volumes do not change significantly
from one iteration to the next. The stability of travel times and volumes must
be reached for all evaluation intervals from one iteration to the next, not
necessarily within one simulation period where traffic conditions may change
from one evaluation interval to the next.
VISSIM offers an automated test for convergence. The Convergence window
for the configuration of the convergence test can be accessed by the
CONVERGENCE button in the Dynamic Assignment window.
Three different criteria for convergence can be selected and the respective
tolerance values set:
638 VISSIM 5.30-05 © PTV AG 2011