VISSIM 5.30-05 User Manual

12 Dynamic Assignment
TO
n,
κ
i
= measured (”observed“) travel time on edge i for period k in
iteration n
T
n,
κ
i
= expected travel time on edge i for period k in iteration n
α = constant smoothing factor (user-defined).
Please note that this kind of smoothed average of travel times includes the
information of all preceding iterations but the “older” an iteration is, the less it
influences the measurements of the current iteration. If a smoothing factor of
0.5 is used, the last iteration n has a weight of 50%, iteration (n-1) has a
weight of 25%, iteration (n-2) has a weight of 12.5% and so on.
MSA
With a new set of measured values, the smoothed travel time is computed as
the weighted sum of
► the old smoothed value (from previous iterations) and
► the newly measured value (from current iteration).
That smoothed value represents the travel time that we expect in the next
iteration.
Formally:
κ 1 κ 1
T
n,
( 1 )
n 1,
TO
n, κ
i
= − ⋅T
−
N n i
+ ⋅
+
N + n i
where
N = user-defined value
K = index of the evaluation interval within the simulation period
n = index of the assignment iteration
i = index of the edge
TO
n,
κ
i
= measured (”observed“) travel time on edge i for period k in
iteration n
T
n,
κ
i
= expected travel time on edge i for period k in iteration n
1
= variable smoothing factor resulting from parameter N and the
N + n
index of the iteration
12.5.3 General Cost
Travel Time is not the only factor to influence route choice. There are at least
two other major influences: travel distance and financial cost (e.g. tolls). In
contrast to travel times these factors are not depending on the traffic
situation and thus have not to be determined by simulation.
622 VISSIM 5.30-05 © PTV AG 2011