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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 info@radixtraffic.co.uk or telephone us on

01794 511388.