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Radix RTM Magnetometer Case Study 1
Customer: Surrey County Council
Contacts: Grahame Bath, Traffic Systems Team Leader & Tracy
Stickler, Traffic Systems Engineer
Location: A324 Pirbright Railway Arch, Connaught Road, Dawney Hill,
Pirbright, Surrey.
On the main A324 at Pirbright in Surrey is a 3-Phase Traffic Signalised Junction which
provides major town links between Guildford to the South, Woking to the East and Aldershot
and Farnborough to the West. A very narrow single file road tunnel carries overhead the
mainline railway link between the South Coast and London. Operating as a shuttle working
system for all three traffic signal approaches means that the junction has to work as
smoothly and efficiently as possible to avoid any delays. The Junction carries high volumes
of commuter traffic, especially at peak hours.
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Problem
There are three ‘All Red’ Inductive Loop detectors installed inside the tunnel at specific
distances along the tunnel’s complete length to detect and extend the passage of vehicles
passing through before the next traffic phase is called. The result is to keep phase delays to
a minimum and optimise flows through this narrow pinch point.
All three loops in the tunnel had started to operate intermittently and begun to exhibit
permanent demand faults, thus extending the ‘All Red’ extension time to a maximum,
resulting in long delays for drivers on each approach.
As this junction is extremely busy with many hundreds of vehicles passing through the tunnel
every hour, a complete closure of the tunnel to repair the detector loops would be very
disruptive and expensive.
Solution
Radix were approached by Grahame Bath, Traffic Systems Team Leader at Surrey County
Council to look into the possibility of using the Radix RTM300/500 Magnetometer Vehicle
Detector to replace the existing faulty inductive loops within the tunnel.
The RTM Detection Solution is normally installed inside cross carriageway ducting below the
road surface at depths of between 150mm-600mm. However, as ducting cannot be installed
across the tunnel carriageway due to the imposed tunnel closure constraints here, another
installation method was to be investigated.
An initial site survey was conducted by Radix Engineers along with Tracy Stickler, Traffic
Systems Engineer of Surrey County Council to test the RTM Magnetometer for suitability at
this site. Existing underground ducting is contained in the footway which runs along the
tunnel’s length and carries the signal and detection cabling for the traffic phase the other
side of the tunnel.
Duct chambers are installed at two locations in the middle and at the far end of the tunnel
where the existing ‘All Red’ loop detector tails are cut back to and connect to feeder cables
back to the Traffic Controller (see figure 2).
As the ducting is very close to the kerb and the carriageway through the tunnel is narrow, it
was decided that it may be possible to detect vehicles in both directions successfully with the
RTM Magnetometer installed parallel with the road inside the actual duct itself.
(The RTM300 Magnetometer has a 3- Axis Magnetometer chip and the orientation of the
sensor is therefore not critical as it is able to detect changes in the earth’s magnetic field
from any direction.)
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The on-site testing equipment was set up and the RTM300 Sensor was pushed down along
the duct for a few metres. It was then connected locally to the RTM500 Interface Card and
testing was started. Various tests were observed using different sensitivity settings and it
was found that at high sensitivity the detection rate was extremely reliable with 99% of
vehicles passing through the tunnel being detected successfully.
Solution Deployment
Following the success of the initial site survey, Surrey CC decided that a proper site trial of
the RTM Magnetometer should take place. On January 15th 2014 three RTM300 Sensors
were installed inside the existing footway ducting at the same positions in the tunnel where
the faulty D2, D3 & D4 ‘All Red’ Loop detectors were located (see figures 1 & 3.). The
RTM300s were then connected to the existing loop feeder cables via re-usable bottle joints
located within the existing duct chambers back to the Traffic Controller. A standard TR2512
detector backplane was fitted inside the detector rack of the existing Siemens 800 Controller
to house the RTM500 Interface Card. Controller input wiring was transferred to the RTM500
and now the junction once again has reliable ‘All Red’ detection of vehicles as they travel in
both directions through the tunnel (see figures 1 & 4.).
Deployment of the RTM detection equipment is always very quick and easy and this site was
no exception, with the total installation time taking less than three hours by Radix Engineers
and Surrey County Council’s nominated Maintenance Contractor, Motus Traffic Limited.
Fig 1, Radix RTM300 Sensor Installation
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Fig 2, Site Layout
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Fig 3, RTM300 Installation Detail
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Fig 4, RTM500 Interface Card installation
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Customer Testimonial
Tracy Stickler, Traffic Systems Engineer for Surrey County Council commented:-
“This junction has always been a problem when it comes to re-cutting the All Red detector
loops under the tunnel bridge, so when they failed again we explored other vehicle detection
options available to us. Lee Shepherd of Radix Traffic described the Radix RTM
Magnetometer technology to us and suggested that it may be a suitable alternative for this
site. Radix were very open and honest in that they advised that the units had not been tried
in this sort of situation before as they are normally installed inside ducts under the
carriageway surface, rather than inside ducting that runs alongside it.
We decided to trial the RTM units and Installation was very quick and easy. The
Magnetometers were carefully positioned along the ducting using rods to be adjacent to the
all red D2, D3 & D4 loop positions and no changes of the controller configuration were
needed. The detectors were to be monitored for an initial two month trial period and a count
via our Remote Monitoring System (RMS) was set up which confirmed that the RTM units
were detecting correctly. In the very early days of the trial a couple of initial faults were
reported via the RMS system. When our signal maintenance contractor Motus Traffic
attended, they reported that there were no actual detection faults on street, reset the fault log
and no more faults have been logged since.
The trial period at this site is now complete and the outcome has been deemed a success
with the junction now operating to its maximum efficiency and minimising any unnecessary
delays to drivers”.
Grahame Bath, Traffic Systems Team Leader for Surrey County Council added:-
"We are very pleased with the way this has worked out. We are always keen to exploit new
technology and saw benefits with the RTM units when first demonstrated to us. Radix have
been very cooperative and have found yet another way to use their innovative equipment.
This has helped us considerably at this difficult site and we look forward to using it at more
locations."
If you require any additional information about the Radix RTM Detection system or if you
require a site survey, then please contact us at [email protected] or telephone us on
01794 511388.