The technological battle to maintain tunnel security 08 Oct 2015

Maurice B. Jones reporting for TunnelTalk
The recent European migrant and refugee crisis has thrown a spotlight on security arrangements at the Channel Tunnel between mainland France and the UK. However, security of underground infrastructure has long been a concern since that project was first proposed, and then cancelled, owing to concerns about Napoleon's armies marching through it. Maurice Jones reports for TunnelTalk on the increasingly sophisticated technological solutions that are available to assist in the security of underground infrastructure.

Transport tunnels, particularly the busiest ones, are noted targets for malicious acts, particularly terrorism. In 1979 the Provisional IRA exploded a bomb near the south portal of the Blackwall Tunnel in London, and there have numerous attacks by individuals and groups on metro systems around the world.

Multi-screens in the Eurotunnel control room necessitate
Multi-screens in the Eurotunnel control room necessitate 'intelligent' systems

As a result of the 9/11 terrorist attack on New York City in the USA, a Blue Ribbon Panel (BRP) of bridge and tunnel experts, sponsored by the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO) convened to examine the security of these critical transport locations, and to develop strategies and practices for deterring, disrupting and mitigating potential attacks. The BRP reported in late 2003.

But other less dramatic, and more common threats to tunnel security exist, the outcome of which is likely to range from loss of revenue, loss or delay of services, structural or system damage, or loss of life.

Overall each tunnel or tunnel complex needs an integrated security system that is designed to handle all likely, and some unlikely, threats, in which all loopholes that might be exploited are closed. Such a system requires information to work well so that preventative measures can be concentrated on the most effective locations.

Information sources

Intelligence on potential threats from far afield should be collected by national and international security agencies, but local information-gathering also has a vital role. Arguably the most important type of information source for local security is visual observation, whether by tunnel staff, specialist security units, or tunnel users and the general public. The work of tunnel and security staff in this regard can be enhanced by the use of CCTV with strategically placed cameras.

Where the potential hazard is not so visible methods outside of the normal visible spectrum have to be employed such as infrared, x-ray or detection equipment to expose the presence of radioactivity.

Other information useful to enhance asset security include detectors at peripheral or zone fences and barriers with various transducers to indicate disturbance at a predetermined level, cutting of the barrier or, in conjunction with CCTV, direct indication of adverse activities.

Installing a Sick laser scanner system to protect a metro tunnel
Installing a Sick laser scanner system to protect a metro tunnel

CCTV and scans

CCTV has long been used to observe situations remotely, but, even with available recording facilities, its success largely depends on the attention of control room staff who may be otherwise occupied or tired from staring at TV images.

More recently, software has become available for automatic analysis of images – connected to an alarm – to warn of potentially unusual situations or objects. Such systems are used in mainly in road tunnels for highlighting potentially hazardous incidents, but they can also be used to indicate unusual occurrences on the approaches to tunnels. Installation is relatively simple and maintenance costs are low.

The introduction of laser scanning has produced a range of improvements over CCTV operations. Laser scanners avoid the main disadvantages of CCTV – poor reaction to changing light conditions, sensitivity to weather, especially rain and snow in external installations, and, especially with image analysis, the need to handle a large amount of data, making reaction times slow.

The Sick group, headquartered in Germany, has developed many CCTV and laser systems for a wide range of industrial applications including transport security. These include a patent for CCTV image quality analysis, usually automatically, using a test pattern.

Tunnel portal scanners to detect incursions
Tunnel portal scanners to detect incursions

Matthias Mezger, Head of Industry Management Building Automation at the Sick Corporate Solution Center Logistics Automation, has introduced a range of laser detector applications of stationery, movable and mobile forms for both road and rail tunnels and metros. The scanners are arranged to create vertical, horizontal or diagonal planes to cover the area of interest and, perhaps, unexpected obstructions such as people on a rail track or walking along a highway carriageway. Multiple-layer or single-lane scanners are available to detect objects at various heights and those approaching the tunnel portal.

According to Mezger, laser scanning is more reliable than a CCTV-based system alone, and cuts down on false alarms. The laser scanner can initially detect an object while a CCTV dome camera at the portal verifies the cause to the operator. Full width tunnel protection can be provided by an ‘optical gate’ that achieves an ‘intelligent’ solution with standard components such as two Sick LMS131 scanners, four DS60 distance sensors to determine train positions, and switching between four fields. A third sensor may be necessary if two trains can pass simultaneously to cover detection in the middle of the portal. Such a system is also used at the end of stations in metro systems.

A combined over-height detection and vehicle identification system has been installed at London’s Blackwall Tunnel to protect the structure that, in the oldest bore, has different lane heights of 4m and 2.8m for each lane. The system combines Over-Height Vehicle Detectors (OVD) and Over-Height Vehicle Lane Detectors (OVLD) from the Coeval Group; and variable message warning signs and a vehicle detection unit both manufactured and supplied by Variable Message Signs (VMS) Ltd; as well as ANPR (Automatic Number Plate Recognition) cameras.

Spike number plate recognition cameras from PIPS Technology as used at London’s Blackwall Tunnel
Spike number plate recognition cameras from PIPS Technology as used at London’s Blackwall Tunnel
Dimensions and temperature scanning before tunnel entry
Dimensions and temperature scanning before tunnel entry

The installation project in 2012 was coordinated by VMS for Transport for London and installed by Serco. PIPS Technology supplied six P372 Spike+ ANPR cameras. These components were used for two systems at different distances (3km and 500m) from the tunnel portal, to alert drivers (by number plate) and divert over-height vehicles to the other lane or alternative routes across the River Thames. David Hargreaves, Principal VMS Engineer for VMS said: “The key of this system is the speed at which all equipment operates to enable the licence plate information to be displayed in time for the driver to view it.”


Perhaps the obvious security precaution is fencing, and the UK government has invested heavily in this simple form of barrier security – plus increased numbers of security personnel – at the Eurotunnel Coquelles site in France.

The recent and extreme cases of migrant intrusion around the Coquelles tunnel portal has demonstrated that even with the back-up of large numbers of security guards and police, sheer force of numbers can effectively bypass barrier methods until the intruders are well inside the tunnel operational exclusion zone. However, the authorities are crediting new fences at Coquelles and Calais-Fréthun station, plus increased numbers of security personnel, with reducing the number of migrant intrusions.

Even supposedly secure transit points through barriers are not really secure unless attention is paid to the system involved. A UK national newspaper reported that some 30 migrants passed through a fence gate into a secure zone simply by noting, through wear to the keypad, which numbers had been used most often and inputting the most likely combinations

Stowaways and smuggling

Until recently, gaining access to a freight container with the intention of either hiding inside for onward transit through cross-border customs and security checks, or for the purposes of smuggling illegal substances, has been a matter of subterfuge but the mass attempts by migrants to cross through the Channel Tunnel have been blatant, defying sealing systems and guards alike. This continues to be a problem although seals can be a continuing deterrent and indicator of wrongdoing.

Universeal offers a wide range of seals for trucks and containers, large and small. At the top end of its range are special Channel Tunnel seals that it supplies exclusively for Channel Tunnel freight to Security Approved Channel Tunnel Freight Forwarders (SACRFF). The Company works closely with the UK Department of Transport to meet the security requirements at the Channel Tunnel using special metal strip and bolt seals.

X-Ray detection

Closed-side containers make it difficult to detect security intrusion targets contained within, whether inanimate objects or human. The deployment of X-ray systems, within a range of non-intrusive inspection (NII) methods, to detect objects in containers is well known and accepted within airport security zones, especially for baggage. But the use of X-rays to scan vehicles and containers for hidden stowaways usually requires higher power to penetrate the steel shell and other objects that may be in the way in the target of interest. Consequently concerns exist over scanning for humans in occupied vehicles, although the possible health effects of this are a matter of dispute.

A gamma-ray image shows two international stowaways inside a truck trailer
A gamma-ray image shows two international stowaways inside a truck trailer

X-ray security scanner technology takes three forms; backscatter, and millimetre wave scanners in active and passive forms. Millimetre wave scanners are used for whole-body scanning although ‘active’ forms are alleged to have safety problems.

Backscatter only requires access to one side of the object, unlike more familiar medical procedures, and is available in large enough machines for scanning vehicles including trailer trucks and containers. It is usually important at tunnel approaches to keep traffic moving at an acceptable pace commensurate with the efficacy of security scanning, so time for results is limited unless larger trucks, for example, are in a holding bay. Fixed or mobile systems are available.

Among those manufacturers producing X-ray inspection systems for vehicles are EAS (Envimet Analytical Systems GmbH) of Brunn am Gebirge in Austria. The CX-3800G is a high-energy gantry X-ray system for the rapid inspection of cargo containers and vehicles. It can be used, EAS claims, to validate manifests in a few minutes, pinpointing weapons, explosives, drugs and other security threats.

Most manufacturers of such equipment are US-based, including American Science & Engineering (ASE under the trade name Smartcheck), Rapiscan Systems (a subsidiary of OSI Systems Inc.), Mobile Search and Smiths Detection. In the UK, Westminster International supplies five different sizes of vehicle X-ray scanners, mostly said to be suitable for occupied vehicles. The company offers consultancy and many types of security solutions that also include perimeter systems, CCTV surveillance, under-vehicle detection, and drone surveillance, plus low-cost operation of surveillance zones through solar lighting.

Maha X-ray Equipments Pvt Ltd of Pune, India, manufactures a mobile system with a scanning tunnel of 2.5m x 2.8m x 5m for vans and buses. The company claims a throughput of 50 vehicles/hour.

Explosives sniffing

Instruments to indicate the presence of explosives by chemical detection of trace compounds are well known Available systems include Thermo Fischer Scientific’s EGIS products.

Puffer machines, as they are commonly known, are explosives trace-detection portal machines used on individuals at security checks. Ion mobility spectrometry (IMS) also enables detection of controlled substances, although a more dedicated system featuring preconcentration technology and mass spectrometry can be 10-100 times more sensitive. IMS ‘puffers’ include the Entry Scan from General Electric and the Ionscan Sentinel II from Smith Detection. Sandia National Laboratories developed the preconcentration technology used by Syagen Technology in its Guardian device.

The loading platforms for Eurotunnel truck shuttle trains
The loading platforms for Eurotunnel truck shuttle trains


Concerns over the large amounts of stolen radioactive material believed to be in circulation around the world, and the risk of ‘dirty bomb’ terrorism, has led to some governments developing suitable high-sensitivity radioactivity monitors. Following installations of the specially developed Cyclamen radioactivity monitor at several UK transport terminals, a special agreement between the UK and French governments paved the way for Cyclamen to be installed within the Coquelles perimeter of the Channel Tunnel. Both fixed and mobile versions of this passive detection system are available and supplied by Serco for use by the UK Border Agency at Coquelles and other international ports.

According to one source quoted in a UK national newspaper: “The point of the Cyclamen machine is that you would need so much lead to prevent detection that no tyres would be able to support a car or truck carrying it.”

Carbon dioxide

Standard gas detectors that sample for carbon monoxide are also being used to indicate the presence of intruders hiding inside freight containers, through sampling exhaled breath. The process tends to be time-consuming when compared to X-ray machines of the correct strength, so such methods can only be a part of a more intensive search. Suitable instruments are produced by Drägerwerk (including gas tubes), Gas Data of Coventry (UK) and Armstrong Monitoring of Ottawa, Canada.


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