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Radix RTM Magnetometer Case Study 2

Customer: Atkins Global/SWTRA

Contact: Tom Siddall, Senior Engineer, Highways & Transportation

Location: A48 Briton Ferry Bridge, Port Talbot, South Wales.

The South Wales Trunk Road Agent (SWTRA), working with Atkins issued a requirement to

upgrade Traffic Signals on the A48 in Port Talbot. Two of these sites are adjacent to the A48

Briton Ferry Bridge (Fig 1) and as part of the upgrade, the sites were to run under MOVA

control and were to have a the speed limit reduced to 50mph.

The A48 Briton Ferry Bridge is an old steel and concrete structure that was built in 1955 and

carries a four lane dual carriageway, plus a combined cycleway/footway that runs adjacent

to the vehicle lanes separated by a safety barrier. The bridge is highly elevated and is in a

very exposed position close to the coast. This stretch of the A48 also acts as a diversion

route should the nearby and adjacent M4 be closed for any reason. This has happened in

the past with the most recent closure occurring during the winter storms in 2013/2014.

Fig 1- General Site Layout

Problem

Due to it’s age, actual construction details for the bridge were not readily available and it was

understood that the road construction above the waterproofing level was only at about 30-

40mm depth. Also, no ducting exists across the bridge. Lamp columns do exist, but no

access in or out of these is possible.

The current sites were running ‘VA’ with loop detectors installed before the start of the bridge

deck.

At Site1 known as ‘Briton Ferry’:- the Bridge Deck starts at 45m away from the Eastbound

stopline. At Site 2 known as ‘Earlswood’:- the Bridge Deck starts at only 5m away from the

Westbound stopline.

To upgrade to ‘MOVA’ operation would require detectors to be located at over 100m+ away

on the bridge deck at each site and with no ducting and shallow road surface, the option to

install conventional loop detection was not an option.

As Site 1 ‘Briton Ferry’ (Fig 2) only required ‘IN’ detection and was technically simpler than

site 2, it was decided to upgrade this junction first and to be used for testing an alternative

detection method.

h

Fig 2 - Briton Ferry Eastbound Bridge Approac

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Challenges

With the need to detect at 100m+ from the Eastbound Stopline approach, and with a shallow

road surface and with no ducting and no accessible lamp columns, the following

technologies were considered but then discounted by Atkins:

Conventional Inductive Loops:- Insufficient carriageway depth to cut loops, no ducting,

difficult to get loop tails off carriageway.

Wireless Magnetometer:- Insufficient carriageway depth to install wireless sensor.

‘Side Fire’ Radar:- Unable to position new poles on bridge deck. Radar could be mounted

on lamp column, but unable to install cables into column.

Long Distance Pole Mounted Radar:- Unable to detect reliably at the 100m+ distance

required.

Video Detection:- Bridge prone to fog and to achieve detection at the 100m+ distance

would require the camera to be mounted high up and therefore not a viable option.

Thermal Detection:- 100m+ detection would require a camera mounted at extreme height.

Slot cut wired Magnetometer:- Carriageway depth an issue to slot cut Magnetometer

sensor in carriageway and with high concrete kerbs, it would also be difficult to get the

sensor tails back to the controller.

Increase Road Depth:- To resurface the carriageway would need significant bridge re-

design to take account of the extra weight, drainage and barrier arrangement.

Do Nothing:- MOVA proven to control traffic well and improve safety at many sites across

the UK & South Wales. The current mode of operation is sub-optimal.

Solution

Radix Traffic were initially approached in March of 2014 by Alastair Gollop - who at the time

was Senior Traffic Signal Consultant for Atkins - to look into the possibility of using the Radix

RTM300/500 Magnetometer Vehicle Detector to provide MOVA ‘IN’ detection for the Briton

Ferry site.

Alastair explained the unusual nature and difficulties of installing conventional detection

(loop/radar etc) to the Briton Ferry bridge structure, and knowing that the RTM Detection

Solution is normally installed inside cross carriageway ducting below the road surface, he

wanted to know if it would be possible to detect vehicles successfully by ‘surface mounting’

the Radix RTM detector on top of the concrete bridge structure adjacent to the carriageway.

However as the main bridge deck structure consists mainly of steel with steel crash barriers

either side of the carriageway and in the central reservation, the concern was that the

performance of the RTM detectors could be dramatically affected as steel contains a high

ferrous content. The other concern was how a waterproof connection from detector wires to

feeder cable was to be achieved.

An initial site survey was conducted by the Radix Engineer along with Alastair Gollop using a

battery powered detector card and sensor (Fig 3) to test the performance of the detector at

the side of the road. Several different installation positions, sensitivities and orientations

were trialled with varying performance levels.

The main findings and reco

1. The results showed

detection level at th

with the sensor plac

sensitivity and insta

2. One sensor should

edge in Lane 2 on t

3. Detection of all vehi

high possibility of H

installed in Lane 1,

Fig 3 - Battery Powered ‘Test’ Equipment

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mmendations from the site trials were:-

that the best position for trying to achieve an acceptable

is site with the high localised ferrous metallic environment was

ed at 40mm from the kerb edge (Fig 4) and set to HIGH

lled between the upright legs of the crash barriers.

be placed at the kerb edge on Lane 1 and the other at the kerb

he central reservation.

cles was possible, however the trial showed that there was a very

GV vehicles travelling in Lane 2 being detected by the sensor

and vice versa for HGVs travelling in Lane 2.

4. Also in Lane 2 there was the high probability of detecting larger vehicles that are

travelling in the outside lane of the opposite carriageway (Fig 5). This could be

alleviated a little by the use of two sensors in Lane 2 set up in the controller software

as uni-directional to only detect vehicles travelling in the correct direction.

5. Suitable non metallic enclosures should be used for the housing/fixing of the sensors

at the roadside to ensure that a suitable waterproof environment exists to make the

electrical connection between sensor and feeder cable back to the controller.

Ducting/conduit for the feeder should also be non metallic.

y

Fig 4 - Sensor testing at Side of Carriagewa

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y

Large vehicle travelling in

opposite direction.

LANE

LANE

Fig 5

5Fig 5 - Possible Detection of Vehicles in Opposite Carriagewa

Proposed Lane 2 Detector

location

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Solution Deployment

From the results of the site survey, it was decided by Atkins & SWTRA that a full site trial

should go ahead using the Radix RTM Vehicle Detectors; one detector in Lane 1 and two

detectors in Lane 2 configured as uni-directional inputs to avoid unwanted detects from the

opposite carriageway.

After a meeting of the Main Contractor, Signal Designer and Signals Contractor, the

following methodology was agreed on how to fix the sensors to the bridge deck and how to

run feeder cables back to the controller:

1. Conventional underground ducting would be installed as close as possible to the

bridge deck with a chamber at the termination point.

2. Above ground mounted steel conduit to be run from chamber to approximately 1m

from the detector position for the feeder cable (Fig 6). Flexible steel conduit to be

used across bridge joints. Secured using short screws into bridge.

3. A waterproof IP rated joint box housing to be mounted at the end of the steel

conduit, to connect the RTM Magnetometer detector to the feeder cable (Fig 7).

4. Plastic conduit from IP rated joint box to be run from the detector position secured

with saddle clips to the bridge deck.

5. Detector to be positioned at the end of the plastic conduit and secured in position by

use of glanded conduit joint (Fig 8).

6. Conventional detector feeder cable used between Radix RTM500 Interface Card in

controller to waterproof joint box.

Installation

The RTM detectors were installed in early August 2014 by the signals contractor and the

initial results of the trial have been very encouraging, with Lane 1 (Fig 9) detecting nearly

every vehicle.

Initially the two detectors in Lane 2 (Fig 10) were not detecting vehicles quite as well, but

after a couple more site visits by Tom Siddall of Atkins to adjust sensor sensitivities, they are

now detecting as well as Lane 1 providing full MOVA ‘IN’ inputs for this bridge approach.

.

Fig 6 - Steel Conduit Containing Feeder

Cable from Controller

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Fig 8 - Lane 1 Radix RTM300 Detector Position

Fig 7 - Steel Conduit Connecting to

Plastic IP Rated Joint Box

ed at End of Conduit

Fig 9 - Vehicle Detection in Lane 1

Fig 10 - Uni-Directional Vehicle Detection in Lane 2

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Summary

The A48 Briton Ferry Bridge presented Atkins and the SWTRA with an extremely demanding

and challenging environment in which to install a reliable and maintainable form of vehicle

detection.

The Radix RTM Vehicle Detector System provided Atkins with an alternative and very

versatile detection solution, where all other vehicle detection technologies could not be

practically or cost effectively deployed.

Customer Testimonials

Tom Siddall Senior Engineer at Atkins. commented: "I am very pleased with the detector

products supplied by Radix, as not only were they extremely easy to install and set up on

site, but they are also effectively maintenance free. I am also very impressed with the

support provided by the Radix team, who were extremely flexible in their approach and were

always available at short notice to provide technical assistance either on site or over the

telephone. They certainly provided us with a cost effective solution on this particular project

where it was looking like there may not be any viable solution available to us, and we are

currently considering their detection products for future schemes and applications".

If you require any additional information about the Radix RTM Detection system or if you

require a site survey, then please contact Radix Traffic at info@radixtraffic.co.uk or on

telephone number 01794 511388.