Technical Bulletin
May 2008
Canoga™ Traffic Sensing System
Accurate Vehicle Detection at Intersections Using
Canoga M702 Non-Invasive Microloops
Introduction
This application note describes the
recommended installation of the Canoga™
M702 Non-Invasive Microloop™, Traffic
Monitoring Card, and C900 Vehicle
Detector, performance-matched components
of the Canoga Traffic Sensing System.
Accurate vehicle-presence detection depends
on several factors:
1. Intersection geometry: lane width,
relationship to breakdown lanes, etc.
2. Traffic-related factors: approach speed,
vehicle mix
3. Accuracy requirement: your requirement
to detect all licensed vehicles while
minimizing the detection of adjacent lane
vehicles
A solution may require a trade-off of these
factors. This application note will help you
understand these factors, enabling you to
tailor your solution to your application needs.
Intersection Geometry
Lane widths generally range from 10 feet to 12
feet. In most instances, one probe per lane is
adequate to detect vehicles in that lane. Widerlane applications may require a non-invasive
Microloop double- or triple-probe set.
A single probe or double-probe set in the right
lane may not detect vehicles that cut the corner
by driving on the shoulder. Consider using a
triple-probe set with one of the probes located in
the shoulder area.
You can make adjustments even after the system
is turned on. If the system misses vehicles
because they travel on the breakdown lane or
because the non-invasive Microloop does not
provide sufficient lane-area coverage, you can
readily add probes or change their locations.
Approach Speed
For advance detection at intersections, use the
guidelines normally used to specify loop
placement for specifying non-invasive
Microloop placement.
Vehicle Mix
Your application’s vehicle mix may determine
the number of Canoga M702Non-Invasive
Microloops you’ll install per lane and their
connection to the Canoga Traffic Monitoring
card or C900 Vehicle Detector. Here’s why.
The system nominally detects a vehicle at a
distance equal to half of the vehicle’s height.
A single-probe set in each lane may not detect
small autos straddling the lane stripe in either
lane. Similarly, they may not detect
motorcycles traveling in the vehicle tire-track
area. A double-probe set with probes four feet
apart will detect the small auto in at least one
of the lanes, and it’ll detect motorcycles when
traveling in or between the tire-track area of
the lane.
If nearly all motorcycles must be detected, use
a triple-probe set with the probes three feet
apart. This will detect motorcycles (and steelframed bicycles) over the center nine feet of
the lane. In problem situations, some agencies
have found it effective to paint a motorcycle
symbol over a probe to indicate to motorcycle
drivers where they should drive or stop.
As a general guideline, adding probes across
the lane increases lane coverage.
For very wide lanes or for unusual situations,
consider using four-probe sets. However, they
may pick up magnetic fields generated by
nearby power lines. In these cases, they
require line-frequency filtering, which
increases scan time. That’s why non-invasive
Microloop sensors attached to vehicle
detectors using line-frequency filtering are best
used only in areas where vehicle speeds are
less than 40 mph.
Stop Bar Detection
At the stop bar region, your detection requirement
most often is to detect all licensed vehicles. The
geometry shown in Figure 1 on page 4 will ensure
that your system consistently detects small
vehicles, including short autos and motorcycles.
Explanation follows.
Canoga™ M702 Non-Invasive Microloop™
Installation
1. Install a first row of Non-invasive Microloops,
a single- or double-probe set per lane, three
feet past the stop bar. This ensures that
vehicles stopping past the stop bar are
detected and a call is held.
2. Install a second row of non-invasive
Microloops, typically a triple-probe set, nine
feet behind the first row or six feet behind the
stop bar. The triple-probe set, with a threefoot distance between probes, ensures that the
smallest vehicle is detected in this region.
Depending on motorcycle-driver habits in
your area, you may find it necessary to use a
double-or triple-probe set in Row 1 and/or
decrease the spacing between Row 1 and
Row 2 to ensure motorcycle detection. Some
agencies recommend painting a motorcycle
symbol over a probe location to indicate
where a motorcycle driver should stop the
motorcycle.
3. Install a third row of M702 Non-invasive
Microloops, typically a single-probe set, 15
feet behind the stop bar or nine feet from
the last row, for detection zones that need
to cover about 20 feet.
4. Install a fourth row of non-invasive
Microloops, typically a single-probe set, 24
feet behind the stop bar or nine feet from
the third row, for detection zones that need
to cover about 29 feet.
5. Install a fifth row of Microloops, typically a
single-probe set, 33 feet behind the stop
bar or nine feet from the fourth row, for
detection zones that need to cover about
38 feet.
Connection to Canoga Traffic Monitoring
Card/C900 Vehicle Detector and
Controller
Connect each row in each lane to an
individual detection channel. Connect the
outputs of the individual detection channels
for a lane in parallel – a “wired OR
configuration” – to the proper controller input.
This helps ensure that all licensed vehicles are
detected and a call is held during their
presence.
6'X6'
Equivalent
6'X40'
Equivalent
3'
9'
9'
6'
3'
3'
36'
9'
9'
6'
12'
Probe sets centered on lane
for North-South Lanes
Probe sets centered 1' north of lane
center for East-West Lanes
Advance
Detection
Probe
Advance
Detection
Probe
Figure 1, Example installation of Canoga M702 Non-Invasive Microloops at an Intersection
Summary
1. All licensed vehicles will be detected when
the separation between the first two rows of
Canoga M702 Non-invasive Microloops is
nine feet. This separation will generate an
effective detection zone approximately
equivalent to a 6’X6’ loop when the loop
detector is set to sensitivity 4 (64
nanohenries).
2. The equal nine-foot separation between the
five rows of M702 Non-invasive Microloops
will generate an effective detection zone
approximately equivalent to a 6’x40’ loop.
3. The number of probes used per lane depends
on the traffic mix and the intersection layout.
The recommended minimum number of
probes per lane is a “1-3” arrangement
progressing to a “1-3-1-1-1” arrangement to
progressively enlarge the detection area. This
flexible approach optimizes the performance
of the detection system at most intersections
while minimizing the cost.
4. Monitor the performance after initial
installation to ensure that all vehicles are
detected. You can optimize the performance
by adding probes, by repositioning probes or
by removing probes – easily accomplished
by removing and reinserting the probe sets
from the pullbox. This can normally be done
with limited, if any, traffic control.
Technical Support
If you have questions or comments
concerning this Technical Bulletin, please
call the Global Traffic Technologies
Technical Service department at: 1-800258-4610
.
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Global Traffic Technologies Canada, Inc.
Canoga and Microloop are trademarks of Global
Traffic Technologies, LLC
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