Quick speed estimates from site geometry.
Estimate credible approach speeds from mapped run-up distance (222), vehicle class (223), gradients/surfaces (227), and observed cues. The helper produces conservative bands and worked examples for VDA reports (221, 229). Use outputs to choose between low-speed and HVM solutions (432–434, 443) and to justify crash rated bollard ratings in design submissions (413, 717). 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.
922.1 Purpose & scope
Turn measured/run-up data into credible speeds for HVM bollard selection (221, 222).
The helper converts site measurements—especially run-up distance—plus surface and gradient notes into approach-speed bands. These bands support a defensible Vehicle Dynamics Assessment (VDA) and help decide between low-speed measures and HVM countermeasures. You can cite the outputs in rating selections and authority submittals (717).
Use it when a full simulation is out of scope but you still need consistency across sites. The workflow aligns with VDA reporting (229) and cross-references estimation methods (224) to demonstrate due diligence.
| Aspect | What matters | Where to verify |
|---|---|---|
| Performance | Tested system (bollard + footing) | How to read crash ratings |
| Operations | Duty cycles, fail-state, safety devices & measures | Automatic HVM Bollard Controls |
922.2 Inputs & evidence
Distances, gradients, surfaces, calming, observed timings/photos (222–224, 227). Store assumptions for crash rated bollard reviews (229).
Capture the straight-line and effective run-up (bends, chicanes), note surface friction, crossfall, and slope. Record traffic calming (speed humps, rumble strips) and any approach vectors that change acceleration potential. Use phone video to time distance–time samples between landmarks. Store photos, GIS measurements, and an assumptions register.
For consistency, cross-link your inputs to run-up distance (222), vehicle classes (223), and terrain & calming (227). This makes later VDA report (229) compilation much faster.
922.3 Methods & models
Distance–time samples and simple acceleration models with friction/grade factors (224, 227). Outputs speed bands.
Use two complementary tracks: (a) empirical timing over a measured span to obtain average speed; (b) a simple segment model that sums acceleration across straight and curved segments. Apply grade corrections and a friction cap so the result remains physically plausible for the surface and vehicle class.
Convert point estimates into bands by bracketing with conservative and optimistic parameters. The helper prioritizes conservative bounds to avoid tier mis-match. Where sites feature curves or pinch points, reduce effective run-up using corner/island geometry (324).
922.4 Sensitivity & safety factors
± bands and conservatism choices (228). Protects HVM bollard decisions from optimism.
Run a small sensitivity analysis for gradient, friction, and run-up. Then apply a documented safety factor to produce a selection speed. This aligns with 228 and underpins the choice between low-speed vs HVM (443). Document your conservatism so reviewers can trace the decision.
922.5 Multi-vector sites
Corners/bays/islands with distinct vectors (225, 324). Worst-credible drives crash rated bollard tier.
Map each vector separately: frontage straight-ons, sweeping corner entries, service-bay cut-throughs. Estimate speeds for each, then adopt the credible worst-case for the rating string and array layout. Use corner/island treatments (324) to limit the riskiest vectors while preserving legitimate access.
922.6 Outputs & reporting
Tables/plots for VDA report (229). Evidences HVM bollard need vs low-speed (432, 434).
Export a summary table: inputs (distances, slopes, surfaces), method notes, speed bands, and chosen selection speed. In reports, place this near the VDA template (229) results and the chosen barrier tier from Design selection guide (432) or Selecting low-speed vs HVM (443). For storefronts or traffic-calming contexts, cross-reference design implications (445).
922.7 Validation & cross-checks
GIS measures, repeat sampling, peer review (224, 118). Confidence for crash rated bollard acceptance.
Re-measure key spans in GIS, repeat timings at off-peak/peak to check stability, and have a colleague perform a peer review trail (118). Keep a tight evidence chain with time-stamped photos and a short methods note. This improves acceptance during authority submittals (717) and reduces rework.
922.8 Save/Export
Report snippets with inputs, photos, Page-IDs (911, 229). Reviewer-ready.
Save a snapshot into your file index (911) with page ID references (e.g., 222, 224, 227, 229) and embed links to the live pages for reviewer context. For UAE submissions, include a brief note on how approach speeds inform the selected barrier rating for SIRA review.
922.9 Pitfalls
Over-estimating run-up; ignoring bends/traffic calming (222, 227). Avoid mis-tiering HVM bollards.
Common failure modes: measuring kerb-to-kerb instead of the true effective run-up; assuming dry asphalt friction in wet pavers; forgetting crossfall; and treating multi-vector sites as a single straight-line case. Each can inflate speed estimates and lead to a tier mis-match or, conversely, overspend. Use 228 to bracket uncertainty and record your assumptions.
Related
External resources
922 VDA Approach-Speed Helper — FAQ
What’s the minimum data I need to estimate approach speed credibly?
Measure effective run-up (not just straight line), note surface type and slope, and capture a short timing video between two known landmarks. Then bracket results with conservative friction and gradient values.
How do speed bands translate into a crash rating choice?
Use the conservative band to pick a selection speed, then map that to barrier tiers via crash-rating guidance. Document the chain from inputs → methods → selection to support authority or peer review.
When should I treat a site as multi-vector?
Whenever distinct approach lines exist—e.g., corner entries, service bays, or sweeping turns. Estimate each vector and adopt the credible worst-case for rating and array layout.
How conservative should my safety factor be?
Follow your governance in 228: show a sensitivity band for key inputs, then apply a documented safety factor that reflects measurement uncertainty and the site’s risk posture.