CPD 05 2024: An introduction to hostile vehicle mitigation

Targeting innocent people to inflict large-scale damage and loss of life has been deemed an effective approach by terrorist organisations around the world. The use of vehicle-borne improvised explosive devices and the more recent spate of vehicle-as-weapon attacks mean that designers, engineers and those involved in the ongoing management of public spaces have a responsibility to mitigate the impact of such attacks wherever possible.

Attacks could potentially occur at any location, and preventing them can prove challenging. This module cannot address the varying circumstances and degree of risk that apply to different facilities. Still, it will provide information on the latest technical requirements, scope of responsibility and best practice for a range of measures that can appropriately aid in preventing loss of life should vehicles be used as weapons.

Learning objectives:

• Awareness of Martyn’s Law and the Protect Duty
• Knowledge of designing for security alongside the latest standards and technical requirements
• Understanding of installation considerations for mitigating vehicle-borne explosive devices

Martyn’s Law

New legislation could ensure that security preparedness is delivered consistently across the UK. Currently being decided in parliament, Martyn’s Law (formerly the Protect Duty) will require many businesses to formally assess the risk of terrorism for the first time. Following the Manchester Arena bombing in 2017, lobbyists developed a two-tiered potential legislation that will impact local authorities, sports grounds and any place that attracts crowds of people.

Past events demonstrate that publicly accessible locations (particularly crowded ones) remain an attractive target for terrorist organisations due to these spaces often being easily accessible, regularly available and offering the prospect of an impact beyond the loss of life alone (such as serious disruption or an additional political or economic impact).

The bill will impose requirements in relation to certain types of premises and events to increase their preparedness for, and protection from, a terrorist attack by requiring them to take proportionate steps, depending on the size and nature of the activities taking place.

The proposals set out different requirements for:

• Standard-tier premises with a capacity of 100-799 individuals
• Enhanced-tier premises and qualifying public events, in both cases with a capacity of 800 individuals or more

Consideration should first be given to the relevance of such measures and whether or not they can be appropriately achieved in any particular case. This could include staff training, cascading information, or an enhanced risk assessment and security plan. If so, the measures should be appropriate, proportionate and balanced.

Premises where qualifying activities take place include:

• Entertainment and leisure, such as museums, galleries and visitor attractions
• Retail, including food and drink establishments
• Sports grounds and temporary event spaces
• Public areas of local and central government buildings
• Places of worship
• Health and education facilities
• Permanent and temporary buildings or locations within a defined boundary

Home Office strategy

It’s important to note that government initiatives are already in place to combat the threat of international terrorism. In 2003, the government devised an integrated counter-terrorism strategy called CONTEST. The aim of CONTEST is to reduce the risk to the UK and its interests overseas from the threat of terrorism so that people can go about their daily lives freely and confidently.

CONTEST aims to achieve this through its four key strands, which complement and reinforce each other to help reduce the overall vulnerability of the UK to terrorism. The fourth strand is the most pertinent to those working in the built environment sector, which states that when an attack cannot be stopped, we must be prepared in order to mitigate its impact. The Home Office worked closely with the UK police and the Centre for the Protection of National Infrastructure (CPNI) on the strategy, with a revised version released in July 2023.

The CPNI (alongside NaCTSO, a police unit co-located with the CPNI) delivers security advice, training and awareness across the national infrastructure. One of its key objectives is to encourage the use of proportionate physical security to protect against vehicle-borne threats, also known as hostile vehicle mitigation (HVM) measures.

Specifying for hostile vehicle mitigation

HVM is a physical security measure that prevents hostile vehicles from gaining close proximity to a site. The objective of HVM measures is to keep vehicles as far from buildings as possible and mitigate the effect of using a vehicle as a weapon. A key element is the introduction of physical security measures — such as barriers, bollards or security gates — tested in accordance with BSI PAS 68 and IWA 14-1.

PAS 68 is the UK industry testing standard setting out the criteria for impact testing vehicle security barriers and providing assurance that products will work as intended when subjected to a horizontal impact.

Originally published in 2013, IWA 14-1 draws on elements from both PAS 68 and ASTM F2656/F2656M (the American standard test method for crash testing of vehicle security barriers). IWA 14-1 aimed to unite and provide a clear, international test certification for security consultants and specifiers to compare HVM products against identical testing methodologies.

The specifications outline a comprehensive testing procedure that simulates various vehicle impact scenarios and covers different types of barriers. A vehicle is propelled towards the barrier at a predetermined speed and angle to allow repetitive and consistent testing. The barrier’s performance is then evaluated based on a set of criteria, including the penetration distance of the vehicle, the displacement of the barrier and the overall structural integrity of the system.

In 2023, ISO 22343-1: 2023 became the new standard for impact testing vehicle security barriers, replacing IWA 14-1. However, the testing criteria have not changed for vehicles, and certification of products tested previously will still be valid.

Designers and specifiers should also be aware of PAS 69, which provides guidance on the selection, installation and use of vehicle security barriers, CWA 16221 (the European agreement that combines PAS 68 and PAS 69), and PAS 170, the test standard for bollards.

Specifiers should be looking for products that have been subjected to a physical crash test to ensure certification and assurance that products will work as intended. Tested products are placed on an approved list that counter-terrorism security advisers (CTSAs) can refer to when making recommendations.

Considerations for secure design

All designs must be taken case-by-case, with designers finding the most appropriate and cost-effective solution. Considerations should include:

• Risk
• Vulnerability and stand off distances
• Installation
• Aesthetics
• Urban design principles
• Inclusive design

Levels of risk

Decisions on counter-terror measures should always consider the attack risk to which the site is exposed. Is it a high-profile building? Or a place of worship? Assessing the risk enables the specification of proportionate security tailored to specific sites, as there is no one-size-fits-all solution. Oversensitivity to risk can result in over-specified, bland and standardised design.

CTSAs undertake detailed site assessments, looking at threats, vulnerabilities and impact should an incident occur. They grade sites based on a risk severity scale:

• High – comprehensive action is required as a high priority to reduce vulnerability, wherever possible and proportionate.
• Medium-high – the consequences of the risk materialising would be substantial. Action is required as a priority to mitigate the risk, wherever possible and proportionate.
• Medium – the risk is not substantial and can be managed via contingency plans. The status of risk should be monitored regularly.
• Low – the risk should be addressed if possible and contingency plans put in place. The risk should be managed at a local level.

Vulnerability

Designers should undertake a vehicle dynamic assessment (which will profile all approach routes) to assess the maximum speeds and angles of attack achievable by a hostile vehicle. Software is given the project layout and will examine the entire scheme and the areas that need to be secured. It will provide information on the largest vehicle that can gain access and the highest speed it can reach, which will help form the security design. The speed of the potential vehicle not only has an effect on cost but also influences which products are suitable.

To reduce vulnerability, worst-case scenarios and potential traffic management plans should be evaluated. Design interventions, including traffic calming techniques, horizontal deflections and slowing traffic in advance of security barriers, can all affect the level of security.

A direct route towards an asset allows a hostile vehicle to build up speed on approach. Meanwhile, chicanes and offset approaches to an asset reduce the speed of hostile vehicle approaches. Moving a road or an asset to create an indirect approach will lead a hostile vehicle away from the asset, while removing vehicle access from the front of an asset removes the potential for using a vehicle as a weapon and establishes a standoff distance from parked hostile vehicles.

It is important that designers understand penetration distances, which begin at the load-carrying area behind the cabin rather than the start of the vehicle and are where the standoff needs to be measured.

Installation

PAS 69 and IWA 14-2 provide guidance on the selection, installation and use of vehicle security barriers to ensure that they are selected and placed as effectively as possible. While IWA 14-1 focuses on the physical product being impacted, IWA 14-2 is concerned with the foundations that it stands upon. One cannot be in place without the other, as the material below ground is often the most important component of HVM.

Key considerations include a maximum air gap of 1.2m between successive faces of HVM barriers, and PAS 68 and IWA 14-1 products must be installed on their tested foundations. When looking at concrete structures, the measurement above finished ground needs to be a minimum of 500mm; otherwise, there is a risk of the vehicle travelling over it.

When working on a retrofit project, it is often impossible to design certain products into the site foundations, making it important to involve your chosen manufacturer early in the design process. A topographical survey that maps the boundaries, features and levels of a site (alongside a utility survey) will reduce the likelihood of problems on site during installation.

Integrated and aesthetic solutions

A decade ago, the industry was limited on the aesthetic options available for HVM products, but that is no longer true. Security and design are not mutually exclusive, and counter-terrorism measures can seamlessly integrate into the public realm.

Overengineered security features will create a sense of distrust in people towards their environment, meaning proportionality is important. While a long line of bollards could make people feel unsafe in a space, options such as planters and seating could blend in with the surroundings while providing the added security needed.

Planters provide an elegant and aesthetically pleasing HVM solution. They enhance the urban landscape with natural elements while providing the durability and strength required to perform in all climates. Planters can be strategically placed to restrict vehicular access and guide pedestrian flow, providing a practical yet decorative addition.

Design-led seating collections provide a simple yet effective way of creating community spaces while providing the appropriate level of protection required. Ranges can include complementary products such as bins, benches and more.

When working with a reputable manufacturer, it is also possible to integrate crash-tested bollard cores into post and rail systems and integrate counter-terrorism design into bespoke features (including walls, signs and ornaments). To ensure an inclusive design, wheelchair users and those with visual impairments must be considered.

Most products are also available as liftouts (where the product is removable) to ensure access when needed for deliveries or maintenance.

It is vital to remember when designing HVM measures that products need to be selected correctly and must meet the applicable standards. It is recommended to involve your chosen manufacturer in the concept and design stage as the foundations need to be considered, alongside how the measures work with drainage and landscaping.

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