Vehicle mitigation in the built environment, by Mark Whyte and Keith McCarthy
The use of barriers to either prevent or channel vehicle traffic and to stop vehicles getting close to high value targets has long been a feature of counter terrorist campaigns and of crime prevention strategies. In this article we aim to provide some historical context to the subject and to demystify some of the science behind the UK standards and the design, selection and application of vehicle mitigation measures in the built environment.
Background
We first witnessed the widespread use of barriers in the UK form the start of the Northern Ireland Troubles in 1969 where they were used to assist in the effective cordon and control of most built up areas and the protection of key points. UCBs โ improvised vehicle blockers comprising 1.5 tons of concrete – became a fixture or the urban landscape, often accompanied by corrugated iron and barbed wire topping. They were ugly structures, purely practical in nature, designed to meet the pressing needs of the time. However, they also had the effect of brutalising urban areas, adding to the general climate of fear and unrest that pervaded thorough much of the seventies and eighties.
As technologies, and terrorist tactics and weapons evolved however, vehicle barriers and associated fortified buildings required to help protect the security forces operating checkpoints needed to become more sophisticated. The effects of blast and the ability of hostile vehicles to crash through barriers were analysed in detail and this data was used in the design and construction of new and replacement VCPs and in the anti-vehicle measures placed around courthouses and other government buildings.
Troubles
Throughout the Troubles though, the primary vehicle borne threat that needed to be protected against was the proxy bomb, with vehicles being used to deliver a device as close to a target as possible with the driver making his escape or, if under coercion, delivering the device and surrendering to the Army or RUC. Suicide bombing, although a growing worldwide phenomenon and a highly effective way of getting a device to the heart of a target, was unheard of in the UK; however in 1990 the IRA did chain three men into vehicles, forcing them to drive to military locations at which point devices in the vehicles were detonated. At Coshquin VCP near Londonderry five soldiers were killed and at Killen near Newry one was killed, with the third device failing to function. These attacks caused such revulsion amongst the population that the tactic was never repeated.
The continuing threat from ram raiding criminals, as well as the changing threat of terrorism, and more specifically the threat posed by suicide bombers in vehicles, has seen physical security barriers become increasingly more sophisticated as well as evident within our contemporary urban environment. The particular threats of VBIED (Vehicle Borne Improvised Explosive Devices) and Hostile Vehicle Attack (HVA) have led to a burgeoning market for robust devices to provide for sufficient bomb-blast stand-off and protection from ram-raid style attacks.
A number of manufacturers have recognised this market, developing their range of enhanced protective barriers and related devices. To provide a level of performance standardisation within the UK market, a new Publicly Available Specification (PAS 68: 2007 – Specification for Vehicle Security Barriers) has been developed with input from barrier experts, security specialists from the Centre for the Protection of National Infrastructure, and the British Standards Institute. This Specification has provided the UK with an alternative to the US rating system, providing information on the levels of dynamic impact resistance of a barrier and how far a hostile vehicle can penetrate the barrier after impact.
In the rest of this article, we will provide a summary of the main types of physical security devices for vehicle threat mitigation – barriers, bollards and blockers – the terminology that surrounds them, and the use of design measures such speed-reducing chicanes that can all assist in helping secure your assets.
Who needs protecting?
The failed June 2007 attacks on central Londonโs Tiger Tiger nightclub and the subsequent attempt to drive a vehicle into Glasgow Airport serve to highlight the HVA threat. Airports, cash centres, financial services data centres, utilities, and corporate offices are all among the potential targets. However, physical security barriers are not only suitable for terrorist threat mitigation, but also to protect locations such as schools, universities, car showrooms and shops from acquisitive attacks by ram-raiding criminals.
Barriers, bollards and blockers
Some sites are able to use natural defences: topographical relief or the presence of water features such as rivers or canals to provide for threat mitigation. However, the site limitations of many buildings – particularly those in urban settings – mean that barriers, bollards and blockers are seen as the answer to many major security concerns. The three principal devices used for physical security and hostile vehicle mitigation purposes are the barrier, bollard and blocker, with most devices being a variation on one of these themes.
Barriers
A barrier can be defined as โanything that prevents access, progress or unionโ. In the context of anti-terrorist measures a security barrier is designed to prevent a rogue vehicle from accessing a site or impacting a particular target. Where a barrier differs from bollards is in providing a continuous blockage over an extended distance. Of course, while in some instances this may only be a few metres, it may also extend over a much greater distance. Equally, a barrier may also take the form of a gate. The seminal anti-terrorist barriers on the British mainland were perhaps the wrought-iron Downing Street gates installed at the behest of then-Prime Minister Margaret Thatcher in 1989. Today, a variety of different access control and security barriers are in place at sites around the UK
Bollards
A basic definition of a bollard is โa short, thick post designed to prevent the passage of motor vehiclesโ. Bollards are generally used where solid barriers are unsuitable. This is generally where pedestrian access is required or where it is aesthetically preferable not to have a solid division, but can also be for reasons of cost or other practicalities. Bollards can be static or retractable (automatic or manually operated). Static bollards are less expensive to install and easier to maintain, but retractable bollards provide threat mitigation while also allowing for the access of legitimate vehicles, such as the emergency services. It is worth noting that many local authorities have regulations for the minimum height of bollards situated in pedestrian areas: commonly 1000mm. Retractable bollards on roadways are invariably much shorter and typical retraction times are in the region of two to four seconds. For hostile-vehicle mitigation PAS 68: 2007 rated bollards should be located a maximum of 1.2m separation. However, such robust – and expensive โ solutions will not always be necessary.
Blockers
Blockers are designed for use on roadways and are normally retractable wedge-shaped devices that, once lowered, will allow vehicles to drive over them before. They come in a variety of sizes, with some of the larger high security blockers measuring as much as 1.2m in height. Blockers can be used to augment existing security devices by, for example, installing them in tandem with access gates or other barriers. Some blocker designs have been extremely successful in impact tests, with only the sacrificial front plate being damaged and the blocker maintaining its functionality after impact.
BSi PAS 68: 2007 and PAS 69:2006
The British Standards Institute specification PAS 68: 2007 Specification for vehicle security barriers was written in order to allow UK-based testing of vehicle barrier systems in a similar way to the US Dept of State โKโ standards. This has allowed British and European manufacturers to test their products for the British and European market using European vehicles. PAS 68: 2007 is complemented by PAS 69:2006 which provides guidance on the selection, installation and use of vehicle security barriers to ensure that their choice and placement are made as effectively as possible. PAS 69 is intended to be used by designers, planners, architects, security managers and facilities managers within the public and private sectors.
PAS 68:2007
Whilst many systems are available that are either promoted or considered suitable for use as vehicle security barriers their characteristics may differ greatly in both function and form, and a comparative means of assessing their performance was required. PAS 68:2007 specifies a classification system for the performance of vehicle security barriers and their supporting foundations when subjected to a single horizontal dynamic impact. It addresses the needs of those seeking assurance that vehicle security barriers will provide the level of impact resistance desired. This PAS identifies impact test tolerances and vehicle performance criteria that need to be met in order to conform to it.
Three alternative assessment methods of determining the performance classification of vehicle security barriers are given:
? The vehicle impact method
? The pendulum method (only suitable for testing bollards at lower energy levels)
? The design method
PAS 68: 2007 rates products by measuring the velocity and weight of the vehicle against the level of penetration of both the vehicle and any of its load past the test product. The maximum level of testing would see a 7.5t (15,000 lb) vehicle travelling at 80km/h (50mph) with zero penetration.
PAS 69:2006
Complementing PAS68: 2007, PAS 69: 2006 highlights the issues to be addressed when considering the use of traffic calming and vehicle restraint systems as part of an overall security regime. The topics considered are by no means exhaustive, and the user is encouraged to consider additional questions and responses to cater for specific issues. If changes are subsequently proposed for the security package that has been designed, decisions based on this PAS should be used to confirm why the original security decisions were made and how they will be affected by any changes. Decisions should be recorded and records retained for audit purposes and periodic review. Vehicle security barriers, by virtue of their basic design, may not be intended to provide any blast resistance but may be affected by any explosives that detonate following the impact or arrest of a threat vehicle. Vehicle security barriers can potentially increase the level of hazard created by an explosion and specifiers should confirm whether this risk is acceptable.
Whatever your security needs, vehicle security barriers should not be considered in isolation but as part of an integrated security solution which may include: adjacent perimeter protection, CCTV, alarm monitoring and guard force activity.
The science โ K and L ratings
These are established by US Dept. of State test procedures in accordance with Standard SD-STD-02.01. This standard specifies a vehicle impact (perpendicular to the barrier) of a 15,000 lb vehicle at a speed of 30, 40 or 50 mph. K-ratings are based on the kinetic energy of the vehicle during impact which can be calculated using the equation:
Ke = _mv_
Where Ke = kinetic energy, m = mass of the vehicle during impact, and v = vehicleโs velocity on impact.
The calculated energies are then assigned representative standard numerical values to represent their magnitude.
The K-rating criteria are:
K4 โ 15,000 lb vehicle travelling at 30 mph
K8 โ 15,000 lb vehicle travelling at 40 mph
K12 โ 15,000lb vehicle travelling at 50mph
L-ratings
L-ratings are used to indicate the actual penetration of the vehicle beyond the barrier for a given K-rated impact. Following an impact test, penetration of the vehicle beyond the barrier is measured to determine the resulting L-rating. Should the penetration exceed 50 feet, the barrier must be retested at a reduced K level. If the penetration is less than 50 ft, the barrier can be rated at that K-rating and assigned an appropriate L-rating
The L-rating criteria are:
L1 – Resulting penetration 20 ft to 50 ft
L2 – Resulting penetration 3 ft to 20 ft
L3 โ Resulting penetration less than 3ft
Chicanes
Whilst barriers, bollards and blockers are primarily designed to prevent access and arrest vehicles, or to allow for their inspection in normal conditions, threat mitigation can also be achieved by slowing the vehicle down. This can best be achieved through the use of chicanes on approach routes towards the target building. A chicane is a sequence of tight serpentine curves in the road which, by introducing a physical deflection into the horizontal path of traffic, causes vehicles to reduce speed. Chicanes can be formed from any manner of materials, but the net effect of slowing down a rogue vehicle is to reduce its kinetic energy and consequently the force with which it would impact its intended target.
Designing a security system
So much for the theory and standards โ what does it mean for the security professional seeking to protect his assets? Physical barriers have clearly moved a long way from the improvisation of the early years in Northern Ireland and with this, and the changing nature of the threat, has come a more structured approach to the design of vehicle mitigation measures and their integration into wider security schemes. The need for barriers, bollards, blockers and chicanes should clearly be considered as a key component of any new development and the findings of the West Review into physical security actively encourages this. A threat and risk assessment will help identify the vulnerabilities and the level of security sought which in turn will help the end user to specify the performance he needs from and help in the selection of appropriate products. The physical protection measures should not be considered in isolation, and will invariable be integrated with technical systems and manned guarding operations. For out of town office and retail parks developments the integration of effective vehicle mitigation measures can be relatively straight forward if considered at the design stage, with hard and soft landscaping can helping augment their effectiveness. Retro-fitting of measures in a dense urban landscape such as the City of London can be a different matter where the ability to interfere with exiting traffic flows is limited and the existence of underground services either prevents the installation of deep seated systems, or is prohibitively expensive.
Looking to the future, it seems clear that physical vehicle restriction measures are here to stay and will become a permanent fixture of the urban landscape, whether to protect against crime or terrorism or merely as pert of architecturally led pedestrianisation schemes. Such measures are likely to become more innovative in their nature as architects and designers seek ways to blend them into the environment, to use existing features and to create increasingly aesthetically pleasing vehicle control schemes. And while there may always be pressing operational requirements that demand the rapid deployment of temporary systems, security professionals will need to work ever more closely with architects and town planners in the design and implementation of vehicle control schemes.
About the writers
Mark Whyte is Director of Security and Explosion Effects Consulting and Keith McCarthy is a security consultant specialising in vehicle mitigation measures, at TPS, part of Carillion plc.
