Vehicle Restraint Systems (VRS) are safety-critical infrastructure designed to prevent errant vehicles from leaving the carriageway and entering hazardous zones. In the UK, VRS are specified and tested to BS EN 1317 — a comprehensive European standard adopted under British Standards. This guide explains everything specifiers, designers, and procurement teams need to know.
What Is a Vehicle Restraint System?
A VRS is any barrier or system designed to redirect an errant vehicle. VRS include:
- Safety fences (guardrails): W-beam (Armco), thrie-beam, and cable systems
- Crash cushions: Energy-absorbing terminals placed in front of fixed hazards
- Vehicle parapets: Barriers on bridge structures
- Median barriers: Central reservation barriers preventing cross-over accidents
- Temporary VRS: Concrete blocks, water-filled barriers used during roadworks
BS EN 1317: The Standard
BS EN 1317 is a multi-part European Standard covering testing, rating, and specification of VRS:
- BS EN 1317-1: Terminology and general criteria for test methods
- BS EN 1317-2: Performance classes, impact test acceptance criteria for safety barriers including vehicle parapets
- BS EN 1317-3: Performance classes for crash cushions
- BS EN 1317-4/7: Terminals and transitions
- BS EN 1317-5: Product requirements and CE marking
Performance Classes: Containment Levels
| Class | Vehicle Mass | Test Speed | Typical Application |
|---|---|---|---|
| N1 | 1.5 tonnes (car) | 80 km/h | Rural roads, lower-risk sites |
| N2 | 1.5 tonnes (car) | 110 km/h | Motorways, dual carriageways (standard) |
| H1 | 10 tonnes (HGV) | 70 km/h | Sites where HGV containment required |
| H2 | 13 tonnes (HGV) | 70 km/h | Higher-risk HGV containment sites |
| H3 | 16 tonnes (coach) | 80 km/h | Very high-risk sites, motorway bridges |
| H4a | 30 tonnes (HGV) | 65 km/h | Critical infrastructure, highest-risk sites |
Working Width Classes (W)
Working width defines how far the VRS and contained vehicle deflect laterally during impact — critical where space is limited:
| Class | Maximum Working Width |
|---|---|
| W1 | ≤ 0.6m |
| W2 | ≤ 0.8m |
| W3 | ≤ 1.0m |
| W4 | ≤ 1.3m |
| W5 | ≤ 1.7m |
| W6 | ≤ 2.1m |
| W7 | ≤ 2.5m |
| W8 | ≤ 3.5m |
In constrained situations — particularly bridge parapets — specify W1 or W2 to minimise deflection.
Occupant Risk Indicators
- ASI (Acceleration Severity Index): Acceleration forces on vehicle occupants. Classes: A (≤1.0), B (≤1.4), C (≤1.9). Lower = better for occupant safety.
- THIV (Theoretical Head Impact Velocity): Theoretical speed at which an occupant's head impacts the vehicle interior. Lower THIV means lower injury risk.
When Is VRS Required?
On UK highways, VRS requirements are set by the Design Manual for Roads and Bridges (DMRB):
- CD 377: Designing for Safety Alongside the Highway
- CD 379: Vehicle Restraint Systems: Performance Requirements
VRS is mandatory on the strategic road network where a vehicle leaving the carriageway could:
- Fall more than 1m to a lower level
- Strike a fixed rigid hazard within the clearzone
- Strike a structure (bridge pier, retaining wall)
On local authority roads, the highway authority applies the same risk-assessment framework with more local discretion.
Specifying VRS: Step-by-Step
- Identify the hazard being protected against
- Determine vehicle types using the road (HGVs, coaches, cars)
- Apply DMRB CD 377 risk assessment
- Select containment class (N2 for most car/LGV roads; H1–H2 for HGV routes)
- Determine working width constraint (available deflection space)
- Select CE-marked product with test evidence for the required class
- Design terminals and transitions per BS EN 1317-4/-7
- Submit to highway authority for adopted road schemes
Barriers Co supplies CE-marked VRS products with full test documentation. Contact us for specification support on your VRS project.