Vehicle Dynamic Assessments

A Vehicle Dynamic Assessment (commonly referred to as a VDA) is a specialist risk assessment that uses digital modelling, site analysis, and expert knowledge to work out exactly what kind of vehicle threat a specific location faces.

It looks at the roads and routes surrounding a site, the types of vehicles that could realistically be used in an attack, and the speeds those vehicles could reach at the point of contact. The result is a set of precise, evidence-based findings that tell you what level of protection you actually need, and where.

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The Vehicle Threat

It goes without saying that not all vehicle threats are equal. The difference between a car driven at 30mph and a heavy good vehicle driven at 500mph is categorically different. A barrier that stops one may be nowhere near sufficient to stop the other.

The variables that define a vehicle threat are:

• The size and mass of the vehicle
• The speed it can reach at the point of impact
• The angle from which it approaches
• How much distance it had to accelerate before reaching your perimeter.

Each of those factors is shaped by the specific physical environment surrounding your site. A long, straight road allows a vehicle to build speed that a narrow, winding street simply does not. A heavy goods vehicle cannot navigate a tight bend at high speed, whereas a car can.

Attacks also come in different forms. A single vehicle driven at speed into a crowded space is the most commonly understood threat, but attackers can also use vehicles carrying explosive devices, or deploy multiple vehicles in coordinated approaches designed to overwhelm or circumvent a perimeter. A thorough VDA considers these scenarios, not just the straightforward ramming case.

Where the VDA Sits in Your HVM Project

A sequence of a well-run HVM project looks a little like this.

It begins with a Threat Vulnerability Risk Assessment, which establishes whether vehicle-borne threat is a relevant risk at your site in the first place. If it is, a VDA follows and this is where the specific nature of that threat gets quantified. The VDA findings then feed into an Operational Requirement, which defines what the HVM scheme must achieve in practice. That informs scheme design and product selection. After that comes procurement, installation, commissioning, and ongoing maintenance, with a commitment to revisit the VDA whenever something material changes, either on site or in the surrounding environment.

The VDA sits at the pivot point of this sequence. Every decision that follows (what barriers to buy, where to install them, how to operate them) is only as sound as the VDA that precedes it. Install barriers without a VDA and you cannot demonstrate that they are appropriate. Over-specify and you waste money and create unnecessary planning and engineering complexity. Under-specify and you leave your site and the people in it exposed. The VDA is what makes the difference between an HVM scheme that is proportionate, defensible, and effective, and one that is simply installed.

Establishing the Risk with a TVRA

A Threat Vulnerability Risk Assessment, or TVRA, is the formal starting point of any HVM project. It checks three things:

• The threat: who might attack this site and with what
• The vulnerability: how accessible the site is to a vehicle-based attack
• The risk: combining both to establish what level of protective response is proportionate.

A TVRA should be conducted by a qualified professional and result in a documented record that justifies the decisions that follow. If the TVRA concludes that vehicle-borne threat is a relevant risk, a VDA is the next step.

For a growing number of venues and sites across the UK, this process is no longer purely voluntary. The Terrorism (Protection of Premises) Act 2025 — more widely known as Martyn's Law, and in force from April 2025 — places a statutory obligation on venues with a capacity of 800 people or more to assess and address terrorism risks, including vehicle-borne threats. With enforcement expected in spring 2027, Enhanced duty venues that have not yet started this process are already behind the curve. The TVRA and VDA together are the primary mechanism for demonstrating that the legislative requirement has been met.

What a VDA Actually Involves

The process behind a VDA is more involved than many clients expect, and that scope is intentional.

It begins with a site survey. The assessor visits the site and examines every approach route, access and egress point, perimeter boundary, and location where people are likely to gather, such as entrances, queuing areas, open public spaces. They are looking at the physical conditions that will either enable or constrain a vehicle threat: road widths, gradients, surface materials, kerb heights, overhead structures, and anything already in place that might affect how a vehicle moves.

Alongside the site visit, desktop analysis is carried out using Ordnance Survey maps, satellite imagery, and CAD or BIM tools where available. Approach routes are profiled in detail including the type of road, how far a vehicle could accelerate before reaching the site, what the surface friction is likely to be, how road conditions might vary with weather.

From there, the assessor builds a picture of the credible threat for each approach vector. This involves profiling the types of vehicles that could realistically access each route. A 30-tonne HGV that cannot make the turning radius into a pedestrianised town centre is not a credible threat on that route. A 3.5-tonne van that can accelerate from a junction 100 metres away very much is.

Digital modelling is used to simulate vehicle behaviour under different conditions such as varying loads, speeds, surface conditions, and weather. Stopping distances are calculated based on vehicle mass, speed, and surface. Turning radii and escape trajectories are analysed. The assessment also considers existing features that may already be limiting threat such as traffic calming measures, road furniture, and tight bends; and models how a hostile vehicle might respond to barrier penetration or deflection rather than a clean stop.

The outcome is a map of the site's specific threat profile: which routes present a risk, what vehicle class and speed represent the credible threat on each, and where the greatest vulnerabilities lie.

What Affects VDA Accuracy?

The National Protective Security Authority is clear on this point: a VDA is indicative, not absolute. The modelled results and real-world vehicle behaviour will always differ to some degree, because real attacks involve variables that no model can perfectly capture.

The experience and qualification of the person conducting the assessment is the most significant factor. An assessor who has conducted hundreds of VDAs across a wide range of sites will read conditions, constraints, and threat scenarios with a level of nuance that a less experienced practitioner simply cannot replicate.

Beyond that, the accuracy of the assessment depends on how well the threat vehicle matches the vehicle classes used in NPSA's testing data, the surface and ground conditions on the day of survey, weather factors that might affect vehicle handling and surface friction, the topography of the site and its surroundings, and the accuracy of the mapping and measurement tools used.

What this means in practice is that the quality of the VDA is only as good as the person carrying it out. A desk-only assessment conducted without a site visit is materially less reliable than one that includes a thorough on-site survey. And a VDA delivered by someone without the right qualifications creates a false sense of security that may be worse than no VDA at all.

Who Should Conduct a VDA — Qualifications and Procurement

The NPSA is specific about who should be conducting and signing off Vehicle Dynamic Assessments. The technical work should be carried out by a suitably qualified and experienced person, ideally an RSES Member Grade specialist with HVM (Category E) classification. RSES stands for the Register of Security Engineers and Specialists, a professional body sponsored by the NPSA. A Chartered Security Professional (CSyP) is also recognised. Ultimately, the assessment should be signed off by an Ordinary or Principal Grade HVM Specialist.

Your local Counter-Terrorism Security Advisor, or CTSA, is a useful early contact. CTSAs are police-based advisors who provide free, impartial guidance to venues and sites on their security posture. They will not conduct a VDA themselves, but they can help you understand whether one is needed and signpost you to appropriate providers.

Before committing to a single provider, seek competing quotes. This not only benchmarks cost but gives you a basis for comparing the rigour and credibility of different providers' approaches.

What the VDA Report Should Deliver

A completed VDA report should identify the credible threat for each approach route: the vehicle class, the achievable speed at the point of contact, and the angle of attack.

From that, it should express the minimum performance requirement for any barrier installed at each position, in a format that corresponds directly to the classification system used by PAS 68, IWA 14-1, and ISO 22343 test standards, so that the findings can be cross-referenced against rated products. If a barrier covering that specification does not exist, or cannot be installed due to site constraints, the report should say so explicitly.

A good VDA report will also identify where operational or procedural changes could reduce vulnerability, either on their own or in combination with physical measures. These might include changes to traffic management, access control procedures, or site operations that limit a vehicle's ability to build speed before reaching a vulnerable point.

The report should be signed and dated, identify the assessor and their qualifications, and describe the methodology used. This documentation is a legal record, and part of the accountability trail that will be scrutinised if things ever go wrong.

From VDA to Operational Requirements

Once the VDA is complete, the next step is to translate its findings into an Operational Requirement. An OR is a formal document that defines what the HVM scheme must achieve in practice.

The VDA tells you what the threat is. The OR tells you what the response to that threat must do, in terms that account for how the site actually operates. That means considering who needs legitimate access, when, and how often, including staff, deliveries, emergency services, contractors. It means deciding how barriers will be operated: whether they are static and permanent, whether they need to be moved or opened, and if so, by whom, how frequently, and under what protocols. It means thinking about what happens at night, at weekends, at times when normal staffing is reduced. And it means accounting for the physical and structural constraints of the site that the VDA has already identified.

From VDA to Product Specification

The VDA report expresses the minimum required barrier performance in terms of vehicle class, mass, and approach speed. This maps directly onto the classification system used by the UK and international testing standards for vehicle security barriers — PAS 68 (the original British standard), IWA 14-1 (its international equivalent), and ISO 22343 (the current international standard that supersedes both).

A test certificate for a rated barrier will state the vehicle it was tested against, the mass and speed of that vehicle, and the penetration distance achieved after impact. All three figures matter. A barrier that stops a 7.5-tonne vehicle at 30mph but allows it to penetrate four metres past the barrier line may still allow a vehicle to reach the asset or crowd it is protecting. Penetration distance needs to be matched against the available stand-off at your specific site.

This is where the VDA's site-specific work earns its value. It is not always the case that you need the highest-rated product available. If the approach geometry of a site means that the credible threat vehicle cannot physically reach the barrier at more than 30mph, then specifying a barrier rated for 64mph or 80mph may be a significant and unnecessary cost. The VDA gives you the evidence to specify proportionately. Equally, if the approach allows a vehicle to reach a high speed, the VDA makes that undeniable and prevents a client from under-specifying to save money in a way that leaves them exposed.

The NPSA's database lists all currently rated and approved vehicle security barriers, searchable by standard and performance level.

For temporary deployments, including events, festivals, public gatherings, the Vehicle Attack Delay Standard (VADS) becomes relevant alongside impact ratings. VADS tests barriers against repetitive ramming rather than a single high-speed impact, which is the more realistic threat at a crowded temporary event where a vehicle might attempt to push through barriers incrementally.

The Golden Thread: VDA as Due Diligence and Legal Protection

In the HVM industry, the “golden thread” refers to the complete, traceable accountability record that should run through every stage of a HVM project. It covers every decision made, by whom, on what basis, and wat standard the resulting measures meet.

If an incident occurs, the questions that follow will be immediate and specific.

A completed VDA, carried out by a qualified and insured professional, does not guarantee that nothing goes wrong. But it demonstrates that the risk was assessed seriously and the decisions were made on an evidence basis.

Martyn's Law makes this more than best practice for a significant portion of the UK's public venues. Enhanced duty venues, those with a capacity of 800 or more, must demonstrate that terrorism risks, including vehicle-borne threats, have been formally assessed and addressed. The VDA is the primary mechanism for proving that vehicle threat has been assessed to the required standard.

When a VDA Is (and Isn't) Required

A VDA is required whenever a site has vehicular routes nearby that could provide an approach vector to a protected area or a location where people gather. That definition covers a very wide range of sites: town centres, event venues, leisure facilities, transport hubs, government buildings, places of worship, shopping centres, schools, data centres, and any location where crowds assemble in proximity to accessible roads.

If a site has no proximate vehicular access and is surrounded by pedestrian-only space, a VDA may not be needed. But that conclusion should itself be reached through a desk-level review, not assumed. The TVRA process will typically identify whether this is the case.

A VDA is also not a one-time exercise. NPSA guidance is clear that it must be reviewed whenever material changes occur: changes to asset locations within the site, changes to perimeter equipment, or changes beyond the perimeter, such as road layouts, traffic schemes, or construction, that could alter vehicle approach speeds or route access. A VDA that was accurate three years ago may no longer reflect the threat at a site where the surrounding road network has changed.

Conclusion

A Vehicle Dynamic Assessment lays the foundation of every HVM decision that follows.

At Townscape Products, our range of rated HVM solutions, including concrete security blocks, planters, and barrier systems certified to PAS 68, IWA 14 and ISO 22343, is designed to meet the full range of threat scenarios that a VDA might identify for your site. If you are at the beginning of your HVM journey, or revisiting a scheme in light of Martyn’s Law, speak to our team. We can help you understand where the VDA fits, what it should practice, and how our products align to the specifications it generates.