Method steps, inputs, assumptions, and outputs.
This is the backbone of evidence-led selection. The VDA method converts site facts into defendable scenarios that justify HVM bollard or crash rated bollard choices. Use inputs from 211–219, pick vehicles (223), estimate speed (222, 224), set vectors (225), and apply factors (228). Record assumptions, produce a clean report (229), and feed results into selection (432–435) and arrays/spacing (321–326, 232). Include one-sentence context that naturally links upward to the parent hubs (this section and the chapter hub). Add SIRA context with a link to SIRA Bollards (UAE) when relevant. Link installation pages only if helpful: What to Expect and Installation Guide.
Important: This is a general guide. For live projects we develop a tailored
Method Statement & Risk Assessment (MS/RA) and align with authority approvals (e.g., SIRA) where in scope.
221.1 Method steps at a glance
Collect site facts (211–219), define scenarios (212), choose vehicles (223), estimate speeds (222, 224), set vectors/angles (225), apply factors (228), and report (229). Outputs drive HVM bollard arrays (321–326) and any crash rated bollard rating choice (411–414).
The Vehicle Dynamics Assessment begins with measurable inputs: run-up corridors, gradients, surfaces, and pinch points. Convert these into a small set of credible worst cases rather than limitless hypotheticals.
Next, select test vehicle classes and masses that reflect your sector risk. Estimate approach speeds from distance and surface conditions, then map approach vectors on plans. Apply sensitivity analysis and a documented safety factor to show margin.
Finish with a concise VDA report that states scenarios, shows diagrams, and names candidate ratings and dependencies. Use the summary to inform array patterning (321–326) and spacing rules (232), and to shortlist products whose certificates match the required crash rating.
| Aspect | What matters | Where to verify |
|---|---|---|
| Performance | Tested system (bollard + footing) | How to read crash ratings |
| Operations | Duty cycles, fail-state, safety | Installation Guide |
221.2 Inputs and constraints
Run-up distance, gradients, calming, and barriers (222, 227), plus crowds and frontage geometry (231, 234). Constraints gate HVM bollard feasibility and whether a crash rated bollard can be founded as tested (332–334, 421).
Start with geometry: run-up distance, bends, surface type, and speed-calming. Note curbs, islands, and street furniture that limit acceleration. Map entry controls and service routes that could alter approach lines.
Then capture installation constraints: underground utilities, available depth classes, and groundwater/drainage risks (243–245, 334). These determine whether a selected product can be installed “as tested” or requires a foundation alternative (332) that still respects rating-critical dependencies (421).
Finally, people and frontages matter: pedestrian flows, accessibility clearances (231), near-door protection (234), and sightlines (237). These inform array density (321) and clear-gap rules (232).
221.3 Choosing scenarios
Screen credible threats by access likelihood and consequence (137, 371). Pick few, defensible cases. These anchor HVM bollard density and the crash rated bollard speed/penetration line you’ll submit (413, 938).
Use a short list of scenario “families” (e.g., straight approach vs. oblique corner) and grade each by approach likelihood, attainable speed, and impact consequences. Document the rationale so reviewers can retrace your logic, linking to the submission-pack guidance (938).
Tie scenarios to security purpose (370–374). For building entrances (371), corner treatment (324), or pedestrianized streets (822), your chosen cases should naturally explain the resulting array pattern and density (321–326).
221.4 Selecting vehicles
Match mass/geometry/ride height to sector risks (223, 137). Vehicle choice changes penetration. Record why selection is right for HVM bollard design and for the crash rated bollard certificate mapping (431).
Vehicle classes (223) should mirror local risk: passenger cars, pickups/SUVs, N2/N3 goods vehicles. Consider unladen mass, load platform height, and bumper geometry, as these affect capture height and penetration. Explain why each class is in or out, citing market-specific requirements (137).
When you nominate a product later, map your scenario vehicle to the certificate’s test vehicle and impact speed string (413, 431). If dissimilar, explain conservatism or provide a reasoned equivalence (414) rather than silent substitution.
221.5 Estimating approach speed
Derive head-on and oblique speeds from measured run-up and surfaces (222, 227, 224). Speeds set HVM bollard tier (123) and the crash rated bollard rating band (413).
Base speeds on measured run-up length, gradient, bend radius, and surface friction; adjust for calming, congestion, and corner pinch points. Use the VDA Approach-Speed Helper (922) to keep assumptions consistent and reproducible across sites.
State a nominal speed and a band (e.g., ±10%) with justification. For oblique lines, present both the path distance and the time-to-impact logic so reviewers can check plausibility. Link your speed choice to tier outcomes (123) and rating bands (413).
221.6 Determining angles/vectors
Diagram vectors on plans/photos (225, 936). Angles alter penetration and gap needs (232). Orient HVM bollard patterns accordingly; confirm crash rated bollard orientation limits (421).
Mark approach vectors on a plan extract and supporting site photos. Use consistent arrow conventions per your mark-up standards (936), and label the impact angle. Note that angle shifts penetration and the needed clear-gap (232).
Where certificates impose orientation limits, call them out and check that your array pattern keeps the tested “face” oriented to likely impact lines. This is especially important around corners and near door protection arrays (323–324).
221.7 Applying sensitivity factors
Use ± bands for speed, angle, and mass (228). Show impacts on HVM bollard count/spacing and on the crash rated bollard pass/fail margin (413).
Present a simple table varying one input at a time (speed, angle, mass). Show how a +10% speed affects penetration and whether the array still meets the acceptance band. Document the chosen safety factor and why it is proportionate to uncertainty.
Use this section to explain trade-offs: extra units, tighter spacing, or a higher rating. Keep the focus on outcomes: safe and buildable arrays that respect utilities (243) and depth limits (244, 332).
221.8 Recording assumptions
State dates, sources, and uncertainties with photos and coordinates (716, 911). This protects HVM bollard decisions from challenge and stabilizes crash rated bollard approvals (717).
Maintain an assumptions register inside your VDA pack: site visit dates, GPS coordinates, photo IDs, measurement methods, and uncertainties. Follow the evidence-capture standards (716) and the file naming rules (911) so reviewers can audit the chain.
Flag any dependencies (e.g., drainage sump required, minimum embedment depth) that affect installation feasibility and rating validity (421). If SIRA scope applies, state it and reference the relevant submittals (717) and the SIRA Bollards (UAE) hub.
221.9 Reporting the result
Summarize scenarios, vehicles, speeds, vectors, and factors with preferred arrays (229, 321). Include the candidate crash rated bollard rating and dependencies list (421, 431).
Use the VDA Report Template (229) to present a one-page executive summary plus appendices (speed calcs, vector diagrams, photos). Name a candidate rating string (413) and declare dependencies that must be built and verified on site (421).
Close with clear recommendations: target array pattern (321–326), spacing rule references (232), and a shortlist of certificate-backed products (431) for the spec (433). This ensures design, procurement, and approvals teams all work from the same VDA baseline (220).
Related
External resources
- NPSA: Hostile Vehicle Mitigation (HVM)
- ASTM F2656: Crash testing of vehicle security barriers
- BSI: Impact test specifications for VSB systems
VDA Method Overview — FAQ
What is a VDA and why do I need it?
A Vehicle Dynamics Assessment turns site measurements into defendable scenarios (vehicle, speed, angle) so your HVM or crash-rated bollard choice is justified. It keeps reviewers aligned and prevents over/under-specification by showing assumptions, sensitivity, and dependencies.
How many scenarios should I include?
Prefer a small set (typically 2–4) that are realistic for the site. Each should state likelihood and consequence, with diagrams and speed estimates. Too many scenarios dilute focus and slow approvals without improving safety.
Can I pick a product before doing the VDA?
No. Do the VDA first to set required rating and array density. Then shortlist products whose certificates match your rating string and constraints (depth, utilities, drainage). This avoids later redesigns and NCRs.
What goes in the final VDA report?
A summary table of scenarios, vehicle classes, approach speeds, angles, sensitivity bands, preferred array/spacing references, the candidate rating string, and a list of rating-critical dependencies. Include plans, photos, and calculation appendices.