As terrorist tactics evolve and shift, countermeasures also need to adapt to create resilience to different threats.

One of the main considerations of counter-terrorism design is preventing unauthorised vehicles from getting too close to, or entering a site or building, and making sure that the integrity of stand-off distances can be maintained.

But where vehicles and crowds are concerned, emphasis is increasingly on the use of hostile vehicle mitigation (HVM) measures such as PAS 68 bollards, barriers and other blocking equipment. These are strong enough to immobilise vehicles and keep them away from pedestrians.  Choosing where to site them is, however, a complicated business. Obviously, there is an understandable desire to make places safer, but given that rogue vehicle attacks are so random, how many places can feasibly be protected and how would installing blocking devices everywhere change how we experience our towns and cities?

What is PAS 68?

PAS 68 is the UK’s standard and the security industry’s benchmark for HVM (Hostile Vehicle Mitigation) equipment. It is the specification against which vehicle security barriers and their supporting foundations are tested with a single horizontal impact to find solutions to prevent vehicle attacks.

PAS 68 identifies impact test methods, tolerances, test vehicle type and vehicle performance criteria that need to be met for a product to be considered secure.

Here are some principles to consider when applying HVM measures.

Keep proportion in mind

Over-sensitivity to risk is an understandable short-term reaction in the aftermath of a terrorist incident and a fortress mentality will seek to install widespread security features.  But if standards are set in times of crisis, there is a danger they can become the norm, and streetscapes become littered with poorly sited blockers and bollards. How can urban design protect against terrorism in a way that is effective, yet does not destroy the vibrancy of an open and accessible city?

The UK Government has an active Crowded Places strategy which seeks to design-out crime and to design-in community safety. A crowded place is considered a location or environment to which members of the public have access that may be considered potentially liable to terrorist attack by virtue of its crowd density. Crowded places would be obvious locations for PAS 68 equipment. If you are in a busy place, have a look around. Chances are there will be PAS 68 kit right there.

Be site-specific

Every scenario will be different and solutions must always show respect for locally distinctive places.

A threat and risk assessment of the site needs to take place within a multi-agency context using various organisations concerned with counter-terrorism security.  This includes a vehicle dynamics assessment of the site to profile the approach routes that hostile vehicles might use to undertake a penetrative attack.

Is the adjoining land traversable?  What are the maximum speeds possible?  What might be the angles of attack?

Countermeasures can then be designed to an appropriate level.  These will range from large-scale site master planning to a micro scale of detailed physical obstacles.

Some sites face restrictions on the physical security measures they can deploy because of planning constraints, heritage considerations, building construction, local infrastructure and services, environmental impact, or a combination of effects from some or all of these.

Find creative and well designed solutions

Urban design measures have increasingly focused on creating liveable places that are inclusive and accessible.

All HVM solutions need to be thought about creatively to find design-led alternatives which do not diminish the look and feel of an open and permeable area but still result in safe spaces.

Places need to remain functional and attractive to the communities that use them.  Security features should be as unobtrusive as possible and subtly embedded within cityscapes.  Street furniture can do double duty and be part of counter-terrorism schemes but it should still be great to use and make a positive contribution to locations.

Slow things down

Some measures are simple but effective.  Good traffic calming measures will reduce maximum hostile vehicle speeds as well as the vehicle’s associated impact energy.  If the approach speed of a hostile vehicle can be reduced, this significantly mitigates its threat.

“A small decrease in velocity = a large decrease in energy = reduced impact = potential for less intrusive, physically smaller and lower cost VSBs” – CPNI.

Vehicle Security Barriers – (VSBs)

Vehicle Security Barriers (VSBs) can be passive (static), or active (operable).  All structural barrier systems dissipate energy and create a hard stop for vehicle attack.  They create optimal levels of security but, if overused, result in a hostile environment.

Active measures include PAS 68 hinged and sliding gates, barriers, operable blockers and bollards.

The most common passive measure is the use of PAS 68 bollards as they maintain maximum pedestrian permeability.  Passive barriers can also be created using street furniture – e.g. PAS 68 benches, planters, cycle stands, lamp posts, bus shelters, information boards – or earthworks, walls, and balustrades.

Installation – key numbers you need to know

All security measures must be managed by an appropriate policy to ensure that they address the relevant security issues to the required level, that they are operated correctly and maintained according to manufacturer’s specifications.  PAS 69 “Guidance for the Selection, Installation and Use of Vehicle Security Barriers” provides design guidance covering this and makes sure that installation is tailored to a specific site’s ground and environmental conditions.

Any physical measure – temporary or permanent – has to be installed correctly for it to be effective. A key factor is spacing. There’s not much point having robust bollards for example if they are very wide apart.

• The maximum clear distance between adjacent VSB elements or other structural elements must be no greater than 1200mm. A visually impaired person (using a cane or a guide dog) needs 1100mm width. A wheelchair user requires 900mm width.  1200mm allows access for pedestrians, wheelchairs and pushchairs whilst preventing vehicles entering a zone.
• The 1200mm clear dimension must be measured between structural elements at a height of 600mm above ground level.
• The minimum height for vertical fixed structures is 500mm.  However, an increased height of 900mm or more will make the measure more conspicuous, assist the visually impaired and typically reduce the penetration of an impacting hostile vehicle.

Find integrated solutions

Any location is multi-layered and complex. HVM schemes must achieve a balance between multiple operational and security requirements

Each site at risk will require various HVM approaches including:

• invisibly integrated components such as structurally enhanced bus shelters, lamp posts, benches or litter bins;
• designed solutions by incorporating public art or local features; and
• physical measures like bollards, blockers, steps and barriers.

Should security be designed-in?

In the UK, there are 13 critical national infrastructure (CNI) sectors: Chemicals; Civil Nuclear; Communications; Defence; Emergency Services; Energy; Finance; Food; Government; Health; Space; Transport; and Water.  All of these are protected to varying degrees. Some are regulated and are required by law to implement security measures within their operations.

However, currently there is no regulatory requirement for designed-in security in the public realm generally and the implementation of design-based counter-terrorism measures has remained in flux. The need for greater urban security is expensive and developers don’t always consider significant security improvements within their designs.  Generally, within the existing built environments, HVM measures will not have been considered at the outset and solutions may need to be retrofitted.  Unless well thought through and designed, these solutions may provide less effective security, be more costly and have a negative visual impact.

Within the current global uncertainty, should there be a statutory obligation for resilience to be designed-in to new and existing buildings so that it is part of the fabric of places?  Design at the outset would be cheaper and more effective than retrofitting.  And designing in security would give greater responsibility to planners, architects and designers to choose better security solutions when they are specifying.  Counter-terrorism measures could be integrated seamlessly into the environment, providing proportionate security whilst still creating beautiful places.

Review the counter-terrorism design standards

UK Standards

CPNI Centre for the Protection of National Infrastructure has published impact testing and installation guidance documents, in the form of British Standards Institution (BSI) Publicly Available Specifications (PAS).

PAS 68 specifies a classification system for the performance of vehicle security barriers, subjected to a single horizontal impact. It provides a common baseline for classifying and comparing VSB systems. In order for a product to conform and be granted a classification, it must meet the impact test tolerances and vehicle performance criteria.

PAS 68:2013 sets out the Impact test specifications for vehicle security barrier systems.

These tests record and report the following:

• Vehicle type
• Test mass
• Impact speed
• Penetration distance
• Distance of major debris

PAS 69 entitled ‘Guidance for the Selection, Installation and Use of Vehicle Security Barriers’ provides design guidance to ensure that equipment is installed correctly – tailored to the individual sites ground and environmental conditions

Some key acronyms
HVM: Hostile Vehicle Mitigation
VSB: Vehicle Security Barrier
VBIED: Vehicle Borne Improvised Explosive Device

International Standards

UK and USA requirements are brought together in the IWA International Workshop Agreements (IWAs).

All vertical elements selected to prevent vehicle access should be fit for purpose and successfully tested or conform to ISO International Workshop Agreement (IWA). See IWA 14-1:2013 – Vehicle security barriers.

Part 1: Performance requirement, vehicle impact test method and performance rating according to ISO “specifies the essential impact performance requirement for a vehicle security barrier (VSB) and a test method for rating its performance when subjected to a single impact by a test vehicle not driven by a human being.”

Part 2: Application “provides guidance for the selection, installation and use of vehicle security barriers (VSBs) and describes the process of producing operational requirements (ORs). It also gives guidance on a design method for assessing the performance of a VSB.”

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