User's Guide

Chapter 4: Operations and Adjustments
RTMS Echo User Guide ©2019 Image Sensing Systems Inc. 4-10
Optimizing Volume Count Accuracy
The most common reasons for vehicle count discrepancies are:
• Zone boundaries overlap or are too close – When this occurs, vehicles
in one zone are shown as being detected in an adjacent zone. This is
referred to as “splashing.” In this case, changing the zone by
increasing or decreasing the boundary can eliminate splashing.
• Improper sensor aiming – When this occurs vehicle counts are below
what is expected. If the sensor is aimed too low or high, or is not
perpendicular to the zone, vehicles may not be detected.
• Obstruction between the sensor and zone – An obstruction, such as a
concrete lane divider may cause smaller vehicles to be missed.
• Occlusion – This is when a vehicle is hidden from view by another
vehicle or object. A large truck can occlude (hide) the detection of a
small car hidden behind.
The following provides information about the possible cause and solution for
various conditions that can cause inaccuracies in the volume count.
Condition A:
Over/Under Count in
Adjacent Zones
In the situation shown in Figure 4-3
, zone 3 shows an over count, while zone 2
shows an under count.
Figure 4-3: Over/Under Count: Adjacent Zones
The above could indicate that vehicles from zone 2 are being detected in zone
3. Fine tune the zone boundary between the two zones.