Hostile Vehicle Mitigation (HVM)
Published 2 November 2020
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1. Introduction to vehicle borne threats
The threats range from vandalism to sophisticated or aggressive attack by determined criminals or terrorists.
- vehicles offer a convenient method to deliver a bomb, known as a vehicle borne improvised explosive device (VBIED)
- a vehicle can also be used as a weapon to injure and kill people, or ram and damage infrastructure
2. VBIED
The effects from a VBIED include the blast, fireball, primary & secondary fragmentation and ground shock. Blast stand-off (the distance between the explosive and the asset) is the single most important factor in determining the extent of damage that can be caused. This is site specific; it is important to maximise the blast stand-off distance. Damage to the asset is reduced in proportion to the distance from the explosion.
3. Vehicle as a weapon (VAW)
A vehicle by itself can be used as a weapon to breach a perimeter in order to injure and kill people, or ram and damage infrastructure. This is referred to as a ‘vehicle as a weapon’ attack. The use of VAW has been used by terrorists to target crowded places and spaces. A broad range of vehicles can cause significant loss of life and serious injury.
There are five main attack exploits used to conduct a vehicle borne attack (VBIED or VAW):
Parked
A VBIED may be parked close to an asset that is the terrorist’s intended target. The blast effects are far greater when the VBIED is closer to the asset. Should a VAW attack be planned, the vehicle may park close to, or inside an event perimeter, where it remains stationary until the time of the attack.
Encroachment
A hostile vehicle may be able to exploit gaps in the perimeter protection, tailgate a legitimate vehicle through a single layer Vehicle Access Control Point (VACP) or drive slowly through what is perceived to be a perimeter or series of obstructions. Alternatively, a hostile could tamper with an active vehicle security barrier to open it in advance of an attack.
Penetrative
A vehicle may be used to weaken and/or breach a building or physical perimeter. A penetrative attack could result in an IED detonating inside a weakened structure. In the event of a VAW attack, this may mean a vehicle aggressively and repetitively ramming through a barrier to gain access.
Deception
A hostile vehicle may be modified to replicate a legitimate vehicle (i.e. “Trojan horse” vehicle). This could be an ex-fleet liveried vehicle, or the occupant(s) of a vehicle may use pretence to gain site access.
Duress
A security officer could be forced to open a Vehicle Access Control Point (VACP) or a legitimate driver could be forced to carry an IED within their vehicle to a vulnerable location.
4. Mitigating a vehicle borne attack
Threats from vehicles can be mitigated by installing physical measures which can be blended into the landscape or streetscape.
These may be passive (static) or active (security controlled) and can be installed either on a permanent or temporary basis.
All such measures should meet appropriate standards in terms of their vehicle impact performance, design and installation. This will depend on the operational requirements applicable to the site. (See 7. Standards and Testing).
4.1 Hostile Vehicle Mitigation (HVM) and Vehicle Security Barriers (VSBs)
HVM uses a blend of traffic calming measures to potentially slow down hostile vehicles and vehicle security barriers to stop hostile vehicles progressing further. There are a variety of HVM and VSB options to assist, reduce or mitigate the threat from vehicles.
These include:
- total traffic exclusion from an area using VSBs
- traffic exclusion using VSBs, but with screening of all vehicles entering the area (with suitable VACP and preferably two layers of active VSB to prevent vehicle tailgating)
- traffic inclusion/free flow within an area, but with all critical/vulnerable assets within that area protected with VSBs
- temporary/supplementary barriers installed at times of heightened threat, or when a secure event is present in the area
4.2 The range of Vehicle Security Barriers include:
- bollards (active, retractable and passive static)
- gates
- planters and strengthened street furniture such as seating
4.3 Landscaping options include:
Ditches, bunds and berms.
The best form of HVM is total traffic exclusion from an area, which should be enforced by appropriately rated and correctly installed VSBs. A deployment of VSBs that restricts traffic (vehicles, pedestrians or both) requires an Anti-Terrorism Traffic Regulation Order (ATTRO), which is recommended by police on the authority of the Chief Officer. (Note: The role may be carried out by a specialist team or officer who exercises the authority on behalf of the Chief Officer).
Installing a static VSB system at a suitable standoff distance from a site will negate deception and duress styles of attack. It can also mitigate tampering and tailgating, which are forms of an encroachment attack. If frequent vehicle access is required into a site, then active solutions should be considered. Manual barriers require subsequent resourcing in terms of staffing, and automated barriers require both proactive maintenance and reactive callout procedures. These solutions are generally more expensive and less secure than a static security barrier system for the reasons outlined above.
If sites are occasionally accessed by vehicles, then it may be more cost effective to use plant-removable barrier systems (for example socketed bollards) rather than installing fully automated active bollards.
5. Temporary options
5.1 Temporary VSBs
Modular units can be interlinked to provide a surface mounted (gravity/free standing) or pinned solution. Some systems can have pedestrian fences mounted on them to give dual purpose protection. Sites or police forces can rent VSBs on a temporary basis. To access these assets you should consult with your local CTSA.
5.2 Vehicles as a barrier
Following an appropriate risk assessment, you may consider the use of a vehicle as a barrier as possible mitigation against a vehicle as a weapon (VAW) attack. This should only be utilised following advice from a Police Security Co-ordinator (SecCo) or CTSA. Such a deployment may impact upon the safety of the event e.g. emergency access, crowd flow rates and evacuation routes. The safety and security of the vehicle drivers must also be considered.
6. Contingency barrier schemes
Repeated renting of temporary barriers is expensive; sites should therefore consider a contingency barrier scheme. These are typically pre-installed gated VSBs in the relevant areas, which can be closed just prior to the event or pre-installed foundation sockets in to which passive or active VSBs are slotted. This avoids the loss of lane availability during the installation of temporary barriers on the days/nights prior to an event; this is beneficial to both communities and transport authorities.
7. Standards and testing
The impact test standards for VSBs are IWA 14–1 and PAS 68, both of which include a range of test vehicles including 1.5t cars, 2.5t 4x4s, 3.5t vans, 7.2/7.5t trucks through to 30t trucks. The results of the tests are classified in terms of how far the vehicle penetrated beyond the VSBs. This “penetration distance” is crucial, particularly when sites have limited standoff between the VSB and asset. Temporary barriers tend to be displaced more by an attack vehicle than permanently installed VSBs, as they do not have the benefit of a structural foundation; this generally results in the attack vehicle penetrating further into the protected space.
Not all sites require protection from the largest or fastest vehicle-borne threats, as the local topography or threat assessment may preclude them. Police CTSAs or skilled security consultants including the Register of Security Engineers and Specialists (RSES) with access to CPNI materials can assess the maximum impact speeds by carrying out a vehicle dynamics assessment. These should be used to scope the most suitably tested and rated VSBs, and/or quantify the residual risks.
Technical requirements
The maximum clear distance between adjacent VSB must be no greater than 1200mm, this distance must be measured between structural elements at a height of 600mm above ground level.
The minimum height for vertical fixed structure is 500 mm. An increased height of 900mm will make the measures more conspicuous
The consequence of not meeting these technical requirements may leave the perimeter vulnerable to a vehicle encroaching through.
Read more: Vehicle as a Weapon (VAW) introduction
Read more: Guidance for Commercial Vehicles
Read more: CPNI’s Hostile Vehicle Mitigation web page – information, advice and guidance