Wavetronix SmartSensor Advance Extended Range (SS-200E) - User Guide User Manual
Page 90
CHAPTER 7 • CHANNELS-ALERTS-ZONES 89
Figure 7.28 – Dynamic Density Filter
Dynamic Density allows the SS200 to generate outputs based on traffic efficiency. The three
filter elements (Headway, % Utilization, and Tuning Factor) are combined with the size of
the zone and the average speed of qualified detections to create a detection density thresh-
old that changes with the fluctuations in detected traffic.
Headway refers to the time separation of the front edge of two consecutive vehicles travel-
ing in a given lane. The headway metric is inversely proportional to the flow rate of a given
lane and is widely used as a measure of how efficiently traffic is flowing in a given lane.
A typical headway value for heavily traveled lanes is two seconds, which corresponds to a
flow rate of 1800 vehicles per hour. In the Dynamic Density settings, the minimum head-
way value is 0.1 seconds and the maximum headway value is 10.0 seconds.
% Utilization refers to the ratio of observed flow rate to ideal flow rate. It is a measure used
to describe traffic efficiency in terms of the ideal efficiency. In the Dynamic Density set-
tings, the minimum utilization value is one percent and the maximum utilization value is
100 percent.
Note
Consider a case where a lane is operating at the lower bounds of acceptable efficiency
when only 75 percent of it’s ideal flow rate was realized. If the ideal flow rate were
1800 vehicles per hour, then the lane is being used adequately at a flow rate of 0.75 *
1800 vehicles/hour = 1350 vehicles/hour (or a headway of 2.67 seconds).
The Tuning Factor is a general-purpose scale factor used to adjust observed results to rep-
resent actual road conditions. The tuning factor resides in the numerator of the Dynamic
Density equation. The initial recommendation for the tuning factor value is to set it equal
to the number of lanes being observed by the sensor. The minimum tuning value is 0.1 and
the maximum tuning value is 10.0.