VISSIM 5.30-05 User Manual

6 The Traffic Network
[OTHER]
● Smoothing factors define the
exponential smoothing of
detector occupancy rates used
by certain signal control
programs.
- Increase defines the weight
of a new occupancy rate in
the new exponentially
smoothed average if the new
rate is higher than the
previous average
- Decrease defines the weight
of a new rate smaller than
the previous average.
● Visible (Screen): The detector will never be displayed if this option is
turned off.
● Label: When showing labels (names) of all detectors (see VIEW -
NETWORK ELEMENTS...) this option allows to individually switch off the
label of that detector.
● Sound: A wave file (*.WAV) can be assigned to a detector. If a sound
card and driver is installed it is played every time a vehicle is detected.
The wave file needs to be located in the same directory as the network
data file (*.INP).
6.7.2.3 Exponential Smoothing of the Occupancy Rate
Exponential smoothing is a way of leveling out the occupancy rate of a
detector. This is necessary because detectors are either occupied or not and
because of that they do not provide enough information to make signal
control decisions. Exponential smoothing allows for calculation of an
occupancy rate using the last t seconds.
This equation is used:
s( t)
= α ⋅ x + ( 1 − α)
⋅ s(
t −1)
The following applies:
s(t) is the new exponentially smoothed value
s(t-1) is the old exponentially smoothed value (recent time step)
x is the new detected value
α is the smoothing factor [0..1]
The new exponentially smoothed value is a weighted average of the new
(detected) value and the exponentially smoothed value after the last
simulation second. The new detected occupancy rate has a weight of α and
the old smoothed value a weight of (1-α). In VISSIM the user can enter two
288 VISSIM 5.30-05 © PTV AG 2011