Wavetronix SmartSensor Advance Extended Range (SS-200E) - Use Manual do Utilizador descarregar pdf (Página 90)

CHAPTER 7  CHANNELS-ALERTS-ZONES 89

Figure 7.28 – Dynamic Density Filter

Dynamic Density allows the SS200 to generate outputs based on trac eciency. e three

lter elements (Headway, % Utilization, and Tuning Factor) are combined with the size of

the zone and the average speed of qualied detections to create a detection density thresh-

old that changes with the uctuations in detected trac.

Headway refers to the time separation of the front edge of two consecutive vehicles travel-

ing in a given lane. e headway metric is inversely proportional to the ow rate of a given

lane and is widely used as a measure of how eciently trac is owing in a given lane.

A typical headway value for heavily traveled lanes is two seconds, which corresponds to a

ow 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 ow rate to ideal ow rate. It is a measure used

to describe trac eciency in terms of the ideal eciency. 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 eciency

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).

e Tuning Factor is a general-purpose scale factor used to adjust observed results to rep-

resent actual road conditions. e tuning factor resides in the numerator of the Dynamic

Density equation. e initial recommendation for the tuning factor value is to set it equal

to the number of lanes being observed by the sensor. e minimum tuning value is 0.1 and

the maximum tuning value is 10.0.

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Wavetronix SmartSensor Advance Extended Range (SS-200E) - Use Manual do Utilizador Página 90