Good To Know About Crash Barriers

A safety barrier is primarily installed to ensure road safety for users of the road network – whether for commercial or leisure transport. Regardless of purpose, the barrier must protect road users in the event of an accident.

Disclaimer: The following text, including any references to products and case studies, is based solely on Danish laws, regulations, and standards. Interpretations and applications may differ in other countries.

Written by: Bjørn Lyng, Project Manager – Road Safety Division

Test Conditions vs. Real-World Performance Can Vary Greatly

A safety barrier is primarily installed to ensure road safety for users of the road network – whether for commercial or leisure transport. Regardless of purpose, the barrier must protect road users in the event of an accident.

However, there is one essential factor regarding the testing of safety barriers that must be considered when selecting a system: the test environment.
Barriers are tested under optimal conditions, typically on compacted sub-base materials like stabilized gravel.
In reality, the conditions are often far from ideal – and as a result, the actual performance of the barrier may differ significantly from the test results. Put simply: the barrier may, in some cases, provide a false sense of security.

As a driver, you want to move safely and efficiently from point A to B.
As a road authority, your goal is that the barrier you install performs as expected when an accident occurs – either stopping or redirecting the vehicle safely.
Problems arise when a barrier does not perform the way it did during the mandatory crash test required for certification.

Before looking at the solutions – which, fortunately, exist – let’s clarify what CE marking really means, and what standards apply to safety barriers.

CE Marking

The European Union promotes the free movement of goods between member states.
To ensure uniform product requirements, the EU has issued legislation requiring all member states to follow common directives. One such requirement is that products must carry a CE mark, which indicates that the product complies with relevant EU directives and harmonized standards.

But note: a CE-marked barrier is not automatically a high-quality or safe solution.

Standards and Norms

Key Terms and Classifications

Working Width (W)

Working width measures the lateral deformation of a barrier during impact. It is a key factor in calculating the clear zone needed behind a barrier to protect fixed objects.

It is measured as the distance from the front of the system (pre-impact) to the furthest rearward movement of the system’s main components (post-impact), including the system width when struck by a heavier vehicle.

There are eight classes of working width, from W1 to W8, depending on the extent of deformation (figure 1). A related term is Vehicle Intrusion (VI), which refers to the space a vehicle penetrates behind the barrier at a given height – important for protecting elements like noise screens, bridge piers, or lighting poles (figure 2).

Dynamic Deflection

This is another indicator of deformation, measured as the distance between the barrier’s front edge before impact and its maximum horizontal displacement. Unlike working width, this is considered the actual deflection and is expressed in meters (figure 1).

ASI – Acceleration Severity Index

ASI measures the physical impact on the driver during a crash.
In short: How dangerous is it to hit this barrier?

In testing, a dummy represents the driver. The ASI value registered on the dummy determines the severity level.
ASI is categorized into:

• Class A – lowest severity
• Class B – moderate severity
• Class C – highest severity

In Denmark, barriers are typically offered with ASI Class A or B.

Containment Levels

This defines how well a system can restrain a vehicle upon impact.

Each containment level corresponds to specific crash tests. New systems must be tested at least twice:

• Once with a light vehicle (to measure ASI), and
• Once with a heavy vehicle (to determine working width).

Containment level classification is based on the heaviest test vehicle. The light vehicle remains constant across tests.

Based on test results, all relevant performance parameters are calculated (figure 3).

Dear Client – Have You Considered the Site Conditions?

Even if a barrier is CE-marked and complies with standards, those two factors alone do not guarantee safety.

As a client or road authority, you should assess the actual soil conditions at your installation site. Soil conditions vary from project to project and have major influence on barrier performance and safety.

Focus on the posts. Using longer posts or embedded plate systems helps ensure anchoring – especially in soft or unstable soils.

Consider Load Testing

You can perform an on-site load test (as used extensively in the UK) to assess whether barrier posts perform as in the test environment.

Using a special test rig, a simulated vehicle impact is applied to the barrier. If the posts fail to meet the required resistance, longer posts or reinforcement plates are used until compliance is achieved.

Final Advice: Involve Your Supplier Early

A specialized barrier contractor brings expertise and practical experience from many projects. Just discussing these topics early can bring you closer to a safer and more reliable barrier solution.

If you wish to peruse our products within crash barriers, then click here.

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