226.1 When multi-hit is credible

Consider queues, convoys, and crowd events (239). If sequencing is plausible, design HVM bollard arrays with minimal single-point dependency, and verify the crash rated bollard’s test basis doesn’t assume one-and-done (411).

Start with a threat-led screen: does the site layout and run-up corridor allow a second vehicle to reach the frontage after a first strike? Check event modes and crowd peaks (239) and whether convoys or tailgating are plausible. Reject far-fetched chains; focus on the credible worst case.

Design intent: avoid arrays that fail from a single damaged element. Where possible, split arrays into short bollard arrays with overlapping fields and no hidden “weak seam.” Cross-check spacing with Spacing rules for HVM & Crash-Rated Bollards (232).

226.2 Time separation assumptions

Define gaps (seconds/minutes) between hits. Short gaps reduce recovery, raising HVM bollard spacing rigor and cooling demands (341, 512). Note whether the crash rated bollard certificate mentions post-impact condition (431).

Specify a time model: T_gap for the second vehicle to arrive and T_recover for systems to reset. If T_gap < T_recover, treat the second impact as acting on a degraded state. For Auto-Hyd systems, include HPU thermal limits (512) and the duty cycle. Record any certificate notes on post-impact operability in Documentation & certificates (431).

226.3 Array fatigue/spacing

Repeated loads can degrade performance; increase redundancy or decrease clear gaps (232, 321). Show that the selected crash rated bollard foundation/detail tolerates cumulative demand (331–333).

Plan for elastic deflection and permanent set from the first hit. If residual set narrows a lane or shifts a line, reduce the clear-gap or add a “catcher” element upstream. Validate foundations via foundation design checks (333) and confirm array patterns in Array Patterns (321).

226.4 Obstruction and queue effects

Parked vehicles, planters, and kerbs alter second-hit vectors (214, 324). Place HVM bollard islands to break sequences. Check crash rated bollard orientation for oblique follow-ups (413).

Second impacts rarely mirror the first. Debris, stalled vehicles, or pedestrian barriers may force a glancing impact at a new angle. Use Perimeter & Approach Paths (214) and Corners, Islands & Pinch Points (324) to place islands that “reset” approach vectors and prevent a straight two-hit line.

226.5 Emergency access conflicts

Ensure blue-light plans survive multi-hit modes (233, 354). HVM bollard overrides remain safe; removable crash rated bollard inserts keep tolerances after drills (626).

Model how emergency/service access (233) works if one element is damaged. Overrides and EFO must never introduce unsafe states; verify logic against EFO & overrides (354). For removable units, re-check keepered openings and alignment (626) after drills or incidents.

226.6 Prioritizing design cases

Rank sequences by likelihood/consequence (221). Pick the worst defendable case to size HVM bollard arrays and to set the crash rated bollard class (413).

Use a simple risk matrix: plausibility on one axis, consequence on the other. Start with the highest-ranking case that is still defendable in budget/space. Tie the chosen scenario to a rating string explained in How to read ratings (413) and document exclusions or non-governing cases in the VDA Report Template (229).

226.7 Documenting sequencing

Flowchart events with timestamps and states (525). This clarifies HVM bollard logic and frames crash rated bollard inspection after any strike (547).

Represent the sequence as a state machine (525): pre-event, impact-1, degraded-state, impact-2, stabilization. For modes of operation (525) include alarms, interlocks, and any incident response (547). Add a post-incident inspection protocol referencing post-incident inspection (735).

226.8 Sensitivity to staffing

Lower staffing raises response time and risk (217). Bias HVM bollard design toward passive safety; avoid relying on manual resets. Note crash rated bollard inspection SLAs in O&M (733).

Where staffing is thin or off-peak windows are long, design for passive resilience: arrays that hold line without human intervention, and minimal reliance on rapid manual resets. Summarize operational assumptions from Operational Constraints (217) and bake inspection/service SLAs into the O&M manuals (733).

226.9 Example scenarios

Corner queue hit → deflected second hit; gate breach then frontage impact. Provide layouts (321–326) and the crash rated bollard band chosen with rationale (414).

Example A — Corner queue then deflection: first strike at a corner island creates debris and a blocked lane; the follow-up vehicle is forced onto a glancing line. Use corner islands (324) and reduce clear-gaps (232) on the secondary line.
Example B — Gate breach then frontage: a breach at an access lane followed by a rush at the main entrance. Split arrays into independent sets (321) and choose rating equivalence via standards equivalency (414) if mixed certificates are used.

226 Multi-Vehicle / Multi-Hit Scenarios — FAQ