Security In Depth: Vehicle Dynamic Assessments. Are They Worth the Investment?

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    The threat of hostile vehicles either delivering an improvised explosive device, driving with intent into crowded spaces or targeting infrastructure has prompted many organisations across the UK to update or implement physical security solutions and, perhaps, for the first time at multiple sites. In this Security In-Depth article,  Lucy Ketley, Sales and Marketing Director at ATG Access and Chris Stevens, Specialist Security and Risk Director at SIDOS, provide an overview of Vehicle Dynamic Assessments, their purpose and key considerations when looking to carry one out.

    The increased awareness of threat and vulnerability has borne a requirement for Vehicle Dynamic Assessments (VDAs). Experts in hostile vehicle mitigation at the National Protective Security Authority (NPSA – formerly the Centre of Protection of National Infrastructure or CPNI) and Counter-Terror Security Advisers advocate that this type of assessment is a necessary starting point and recommend such a process. A VDA is a long-established technical component of HVM schemes and is essential to identifying residual risk, enabling the execution of a robust and appropriate defence for vulnerable targets.

    So, why is it that some clients choose to forego a VDA? Clients know a VDA is essential, but perhaps not quite how important and the extent of its value.

    In this Security In Depth, we explore the importance and, crucially – the value – of VDAs in detail and explain why it is always a worthwhile investment.



    Is a VDA Required?

    Often, there is an obvious case for a VDA on the basis that HVM is already a consideration in a scheme. But there is always a possibility that the clients for whom you work (or perhaps you are the specifying company?) won’t know if HVM is required or how to begin the threat identification process.

    In these cases, it is recommended that a threat and vulnerability assessment is undertaken ahead of a VDA. This is also true for sites where HVM demand has not been identified, but the landscape is changing. i.e., you may have three locations in a project, of which two have never been threat assessed. At this point, you should:

    • Undertake a risk assessment for each location in a project.
    • Determine the threats and vulnerabilities facing each location.
    • Work with someone experienced with HVM in a counter-terror context.

    But, assuming the need for HVM has been identified, a VDA should follow and, broadly speaking, will consider the following elements:

    • Existing security measures, procedures, and practices.
    • All potential routes a vehicle could negotiate to the point of contact.
    • The type of vehicle that could negotiate said route, i.e., HGV, Van or Saloon
    • The speed a vehicle could achieve along that route.
    • The weight of the vehicle that could negotiate the route, i.e., 3.5-ton, 7.5-ton, 7.5 ton laden to 18 ton, or fully laden HGV at 30 tons.

    Choosing Your Vehicle Dynamic Assessment Scope and Skills

    A Vehicle Dynamic Assessment (VDA) is part of an extensive, specialist process to procure Hostile Vehicle Mitigation (HVM) measures. The first question to ask and answer is whether hostile vehicle mitigation is required as a proportionate security measure. This will come from an internal or consultant-led ‘Threat Vulnerability Risk Assessment’ (TVRA). The TVRA will provide a documented record of the threats considered and justification for physical security measures.

    A VDA assesses the vehicle threats, vulnerabilities, and approach speeds around project sites, crowded spaces and other infrastructure which may involve multiple access and entry points.

    Formal VDA scoping will be unfamiliar or new to most clients or project managers. It’s essential that its complexity and criticality are appreciated and that all stakeholders are clear on the importance of preliminary scoping. After all, it is a precursor to every HVM decision made thereafter.

    Before heading into a VDA and engaging with an advisor, it is crucial to establish a clear scope of VDA requirements to ensure the right level of risk is mitigated. (i.e., locations, whether for counter-terror purposes only, crime prevention or both and what threats and vulnerabilities exist per site). A client may seek the VDA to assess locations already identified as requiring protection or seek the advisor to carry out the identification themselves. Correspondingly, a full TVRA and VDA for a site may be sought. Whichever option is chosen, there is a need for a clear scope to ensure clients are not ending up paying more than is required, ensuring they have a robust record detailing stages of the security decision-making process.

    If you need support to achieve this, look for professional persons or organisations experienced in delivering VDAs in an HVM, counter-terror context. Ideally, their capability should come on recommendation, too. Where an organisation is selected, the same assurance of credentials should apply to the specific individual who’ll eventually conduct the VDA.

    Starting the Vehicle Dynamic Assessment Process

    A VDA may be your first advisory step in a security scheme or the progression of a process already in hand.

    Regardless of the stage you are currently at, it is wise to familiarise yourself with VDA-associated liabilities. We explain this in-depth here, but in short, whoever provides the VDA assessment is liable for the recommendations made. As a result, it is critical that VDAs are scoped and performed as per best practice and that the individual conducting the assessment is suitably certified, experienced and appropriately insured.

    VDAs and the “Area of Probability”

    The core purpose of a VDA is to verify appropriate products to be selected to mitigate hostile or errant vehicles from breaching the identified location assessed. In addition, the VDA can be used to confirm that the products installed are appropriate for the calculated speed of vehicle sizes and weights that can realistically encroach on the specified locations.

    On paper, that can sound somewhat formulaic, but the reality of VDAs and subsequent recommendations are altogether more nuanced. That’s because with security, especially in an HVM counter-terror scenario, almost anything is possible, but not everything is probable.

    That area of “probability” is where the vulnerability lies. So, that is where decisions must be focused. Fixed calculations may overlook game-changing context resulting in under or over-specification.

    For example, bollards capable of stopping a 7.5 ton vehicle to a 5 metre penetration depth are recommended. But there is only space for bollards 3 metres from the building lobby. On the other hand, HVM may be recommended to stop HGVs approaching at 50mph, despite natural obstructions on approach (such as narrow and windy streets) making the vehicle size and speed impossible. A security professional will notice these nuances immediately.

    There can be road conditions where the identified threat cannot be mitigated. The client will be made aware of this through the VDA process and will therefore be conscious of this residual risk.

    In summary, VDA work is less a numerical exercise and more of a balancing act between probability proportionality and the stopping power of a specified product. Understanding that and knowing how to use it is key requirement clients should seek from the appointed advisor.

    What Value Does a VDA Provide for a Client?


    From a client’s perspective, the greatest value of a VDA is the certainty it offers. As a result of the calculated assessment and transparent, accountable (and ideally underwritten) advice, clients can unequivocally prove that their HVM solution is appropriate for the threat a site faces.

    Simply put, clients can rest assured that they have the best option to mitigate risk and can track every decision back to that crucial VDA.


    A blanket “golden standard” approach – when the highest specification product is chosen regardless of calculated threat – is relatively standard. However, it is not always justifiable.

    That’s because to be justifiable and appropriate, HVM recommendations must be sustainable proportionate, achievable, realistic, and ultimately effective as per specific VDA findings. And that doesn’t always mean defending against 7.5 tonnes at 50mph if such a threat isn’t viable (i.e., a speed-limiting obstruction).

    Take, for example, a scenario where a client could deliver appropriate and proportionate HVM by installing solutions that protect against 7.5 tonnes at 30mph. That represents a value-saving opportunity for the client whilst ensuring HVM remains effective and proportionate.

    Sometimes, the best product option to mitigate risk may not exist or be installable due to ground conditions or obstructions. In these scenarios, an engineered solution is required, but up to that point, existing tested products will fit with VDA advice.


    When a VDA is delivered, those individuals would be liable for the HVM calculation provided.

    So long as a client acts on this advice, maintains regular inspections, doesn’t modify products, and manufacturers install products correctly, legal liability rests at the door of the advisor who provided the assessment concerning vehicle size and speed following a VDA.

    Theoretically, if a VDA was scoped, run and interpreted as per best practice, there is no cause for concern. However, a crucial component of this is insurance. Independent Security Consultants can obtain insurance and underwrite the recommendations they make when completing these tasks using all skills and experience.

    Although the UK has yet to charge a Security professional, that’s not to say prosecutions won’t happen. For example, while still a draft bill, the Protect Duty is set to reframe liability in HVM and other security situations. The best option for all parties is to place VDAs and advice into the hands of a counter-terror specialist with experience in HVM threats.

    The Importance of a VDA to The Golden Thread Principle

    The golden thread is an accountability principle whereby a trail of every HVM decision is logged and accessible. The golden thread of security covers every stage of a project and every stakeholder involved, spanning from credible assessment (e.g. threat assessments and VDAs) through to tested products procured, installed and maintained to manufacturer standards and operated as intended.

    As one of the first stitches in the golden thread, a VDA is crucial to liability mitigation. In fact, if the worst were to happen, it would be the subject of immediate questioning: was a comprehensive VDA completed, who conducted it and made recommendations, and can it be produced?

    A VDA demonstrates due diligence as part of the golden thread, and when completed by an insured expert, the chances of being convicted in court reduce enormously.

    In Summary, a VDA is Always Worth the Money

    VDAs deliver substantial net benefits for what amounts to minimal cost in the grand scheme of an HVM project. For a typical project, VDAs generally cost a few thousand pounds – negligible compared to expensive and over-specified HVM solutions.

    And in almost every scenario, money will be saved by undertaking a VDA. If engaging with the right Security Consultant, you fully understand risk and know whether HVM solutions are appropriate or excessive. That means clients spend only the money they need to pay, crucially while maintaining an evidence trail that admonishes them of some risk liability.

    How to Procure a Credible and Professional VDA

    A credible and professional VDA depends on the specialism and experience of the individual running the assessment and giving advice. A VDA provider must provide clients with several assurances that they are correct for the job, which we have compiled in the following checklist:

    • Transparency: A VDA provider must be clear about what is being paid for as part of a VDA. This includes being transparent about what clients need as part of their VDA to mitigate overspend. For example, unless a bespoke engineered solution is required, a client does not need to have kilojoule energy at the point of contact calculated.
    • Advice only: A VDA provider should be providing advice only. Their function is not to define scope, nor should they recommend specific products or providers. (One exception to this rule is when a specific and bespoke solution is clearly required)
    • Rationalisation: A VDA provider will clearly explain why a client should consider HVM recommendations with evidence of strategic and critical thinking, i.e., looking at points of failure and not just points of success.
    • Referrals: Wherever possible, choose a VDA provider who has been recommended to you and comes with ample references.
    • Proof of execution: The scope of security is vast; therefore, a VDA can be similarly extensive. To ensure that the right level of risk is mitigated, work only with professionals who can prove successful execution of VDAs on similar projects to your own. Ensure you have a clearly defined scope before engaging in the VDA process so the intended outcomes are clear.
    • Accountability: A VDA provider must have the right level of insurance and have their recommendations underwritten. They will be committed to upholding the golden thread and could readily stand behind their rationale in court if necessary.

    As a responsible HVM product manufacturer, ATG has a unique insight into VDAs and the wealth of value they offer to clients. From protecting against legal recourse to uncovering cost-saving opportunities, a VDA is always a worthwhile investment.