Introduction
This article explains what passively safe means for road sign supports and summarizes the guidance from BS EN 12899-1:2007, specifically Annex K, concerning aluminium sign posts. In general, small-diameter, thin-walled posts can be considered passively safe—that is, they bend or shear on impact to reduce injury risk—without requiring crash testing.
What Does “Passively Safe” Mean?
A passively safe sign post is designed to reduce harm to vehicle occupants during a crash. If struck, the post yields, collapses, or detaches to avoid causing serious injury. This concept applies to supports for:
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Road signs
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Lighting columns
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Signals
The performance of these supports is formally assessed by BS EN 12767, which defines crash test classifications (e.g. "100NE"). However, certain small posts are automatically “deemed to comply” under BS EN 12899-1:2007, eliminating the need for crash testing.
Aluminium Sign Posts: Passive Safety Criteria
According to BS EN 12899-1:2007 Annex K, aluminium sign posts are deemed passively safe without testing if they meet the same strength limits as compliant steel posts.
✅ Deemed Passively Safe:
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Material: Aluminium (or steel)
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Maximum diameter: 89 mm
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Maximum wall thickness: 3.2 mm
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Support type: Single post or multiple posts with proper spacing
Aluminium posts are generally less stiff than steel, so an aluminium post of the same size will behave similarly—or more safely—in a crash scenario.
Summary Table: Deemed Passively Safe Sign Posts
| Configuration | Diameter & Wall Thickness | Additional Notes |
|---|---|---|
| Single post | ≤ 89 mm OD, ≤ 3.2 mm wall | No further testing required |
| Two or more posts (≥ 1.5 m apart) | Each ≤ 89 mm OD, ≤ 3.2 mm wall | Must be spaced to ensure only one post is hit |
| Two posts (< 1.5 m apart) | Each ≤ 76 mm OD, ≤ 3.2 mm wall | Minimum spacing between posts: 750 mm |
Important: Posts must not be rigidly braced. Only the sign plate may connect them.
Related Standards
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BS EN 12767: Defines crash testing and classification of supports
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Passive Safety UK Guidelines: Offers practical design advice for safe roadside structures
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DMRB CD 377 & CD 353: Apply passive safety principles to road signs and supports
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IHE Sign Structures Guide: Best practice for specifying and verifying structural safety
Recommendations for Sign Makers and Installers
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Use aluminium sign posts ≤ 89 mm x 3.2 mm to comply with passive safety without testing
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For multi-post supports, observe minimum spacing and diameter rules
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Avoid larger/stiffer posts unless they are tested to BS EN 12767
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Refer to manufacturer documentation when selecting proprietary passive-safe systems
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On roads ≥ 50 mph, passive safety is often mandatory in local authority and National Highways schemes
Conclusion
Yes, aluminium sign posts can be passively safe. If the post is ≤ 89 mm in diameter with a ≤ 3.2 mm wall, it is deemed passively safe under BS EN 12899-1:2007. This means sign makers can use them in road-side installations—especially on high-speed roads—without requiring crash testing, as long as post spacing and structure rules are followed.