Hostile Vehicle Mitigation (HVM) Systems & Barriers

Overview

Hostile Vehicle Mitigation (HVM) systems are physical security measures designed to prevent, stop, or mitigate hostile vehicle attacks, including:

• Vehicle-as-a-Weapon (VAW) attacks
• Vehicle-Borne Improvised Explosive Devices (VBIEDs)

HVM systems differ fundamentally from conventional access control or traffic management barriers. They are security-first, defence-led installations, where threat mitigation takes precedence over convenience, vehicle protection, or user comfort.

As a result, HVM systems often behave in ways that appear aggressive or counter-intuitive when compared to standard parking or access bollards.

Typical Deployment Environments

HVM systems are commonly deployed in locations where the consequences of hostile vehicle access are high, including:

• Transport hubs and stations
• Government and local authority buildings
• Ports and maritime infrastructure
• Stadia and major event venues
• Critical National Infrastructure (CNI)
• High-footfall urban public realm locations

Threat Models Addressed

HVM systems are designed to counter:

• VAW (Vehicle-as-a-Weapon) Deliberate vehicle ramming intended to cause casualties.

• VBIED (Vehicle-Borne Improvised Explosive Device) Use of a vehicle to deliver explosives close to a protected asset.

• Tailgating / Forced Entry Closely following an authorised vehicle to breach a secure perimeter.

Common Types of HVM Barriers

Rising Bollards (HVM-Rated)

• Hydraulically or electro-mechanically operated
• Crash-tested to PAS 68 or IWA 14-1
• Designed to immobilise or destroy vehicles
• Fast deployment times prioritised

These are the most common automated HVM barriers used in constrained urban environments.

Road Blockers

• Large steel wedges or plates that rise from the roadway
• Extremely high stopping capability
• Suitable for heavy vehicles and high-energy impacts

Often used in ports, embassies, and high-security perimeters.

Fixed Barriers & Passive Measures

• Reinforced planters, benches, street furniture
• Structural barriers integrated into landscaping
• No moving parts or control systems

Typically used to create hostile-vehicle stand-off distances.

HVM-Rated Gates & Sliding Barriers

• Reinforced foundations and locking points
• Designed for impact resistance, not throughput
• Usually slower and manually supervised

Design Philosophy

HVM systems are intentionally designed around the following principles:

• Defence over convenience
• Fail-secure rather than fail-safe
• Assume hostile intent until proven otherwise
• Aggressive response to ambiguity
• Automated access is secondary to security

This philosophy directly influences how HVM systems behave in live operation.

Automation in HVM Systems

Overview of Automated Operation

Many HVM installations incorporate automated access for authorised vehicles, typically via:

• Intercom systems
• Guard control panels
• Timed or conditional lowering of barriers

However, automation in HVM systems is deliberately restrictive and tightly controlled.

Unlike conventional access barriers, automation is not designed to accommodate hesitation, reversing, or abnormal vehicle manoeuvres.

Vehicle Detection Methods

Most automated HVM systems rely on inductive ground loop detectors.

Ground Loop Operation

• A magnetic field is generated within the loop
• When a vehicle passes over, the inductance changes
• The controller interprets this change as vehicle presence

Ground loops detect metal mass, not:

• Vehicle intent
• Direction of travel
• Speed or driver behaviour

Dual-Loop HVM Logic

A common HVM configuration uses two ground loops, typically positioned:

• One on the secure side of the barrier
• One on the non-secure side

The control logic is designed to:

1. Lower the barrier when authorised access is granted
2. Detect vehicle entry onto a loop
3. Monitor loop occupancy and clearance
4. Immediately raise the barrier once a loop is cleared, indicating the vehicle has exited the protected zone

This logic exists specifically to counter tailgating and forced entry.

Aggressive Raise Behaviour (By Design)

In HVM systems:

• The barrier may begin preparing to raise as soon as a vehicle is detected entering a loop
• Once the system believes the vehicle has cleared the detection zone, the barrier will raise without delay

If a vehicle:

• Hesitates
• Reverses
• Rolls forward and backward
• Stops partially over a loop

…the system may interpret this as the vehicle having exited the secure area and will deploy the barrier.

This behaviour is intentional, compliant, and expected in an HVM context.

Why This Differs from Standard Access Control

Standard access or parking bollards typically prioritise:

• Vehicle safety
• User convenience
• Obstruction detection
• Predictable driver behaviour

HVM systems do not.

In an HVM environment:

• Failure to stop a hostile vehicle is a higher risk than damaging an authorised one
• Safety sensors that could delay deployment are often omitted
• Ambiguous vehicle movement is treated as a potential threat

Manual Operation & Best Practice

Manual Mode

Most automated HVM systems provide a manual control mode, in which:

• Ground loop inputs are ignored
• The operator directly controls barrier movement
• Deployment is supervised visually

Recommended Use of Manual Mode

Manual operation should be used when:

• Long vehicles (e.g. lorries) are passing
• Multiple vehicles are travelling in convoy
• Vehicles may need to stop, reverse, or manoeuvre
• Escorts or abnormal movements are expected

Best practice: Any vehicle movement that does not involve a single vehicle passing cleanly and continuously should be managed in manual mode under security supervision.

Safety Considerations

HVM barriers are not primarily safety devices.

Common characteristics include:

• No pressure edges
• No photocells or obstruction detection
• No automatic re-opening on contact

This is consistent with their security role and threat model.

Standards & Guidance

HVM systems are typically designed and assessed against:

• PAS 68 - UK impact testing standard (legacy but still referenced)
• IWA 14-1 - International vehicle impact test standard
• ISO 22343-1 - Vehicle mitigation barriers
• NaCTSO / CTSA guidance - UK counter-terrorism protective security advice

Final design should always be informed by:

• Site-specific threat and risk assessments
• Police or CTSA input
• Operational requirements

Maintenance & Lifecycle Considerations

HVM systems are mechanically intensive and require:

• Regular inspection for impact damage
• Hydraulic servicing (where applicable)
• Control logic verification
• Periodic major servicing, often requiring removal from ground

Repeated low-speed impacts are common and do not necessarily indicate failure, but they do accelerate wear and servicing requirements.

Post-Collision Inspection & Impact Response (Best Practice)

Why Post-Collision Inspections Matter

HVM systems are designed to be struck by vehicles. Even low-speed or “non-hostile” impacts can transfer significant energy into:

• Structural foundations
• Hydraulic assemblies
• Drive mechanisms and seals
• Anchor points and reinforcement cages

While many impacts may not result in immediate or visible failure, hidden damage can compromise performance during a genuine hostile event.

As such, post-collision inspection should be treated as best practice, in addition to scheduled preventative maintenance.

What Constitutes a “Collision”

A post-collision inspection should be considered following any unplanned vehicle contact, including:

• Vehicles mounting or striking raised bollards
• Vehicles driving over partially raised barriers
• Slow-speed manoeuvring impacts
• Reversing or turning collisions
• Repeated “nudges” or scrapes over time

Impacts do not need to result in visible deformation to warrant inspection.

Recommended Post-Collision Actions

Following a collision or suspected impact:

1. Record the incident

   • Time and date
   • Vehicle type and direction of travel
   • Barrier state at time of impact (raised / lowering / raising)

2. Carry out a visual inspection

   • Alignment and verticality of bollards
   • Signs of cracking, distortion, or abnormal movement
   • Oil leaks or hydraulic residue

3. Functional testing

   • Raise and lower cycles
   • Synchronisation between multiple bollards
   • Abnormal noise, vibration, or speed changes

4. Control system checks

   • Fault logs and alarms
   • Confirmation of correct detection behaviour
   • Verification of manual override operation

Major vs Minor Impacts

• Minor impacts may only require logging and monitoring

• Repeated impacts should trigger increased inspection frequency

• Significant impacts (including any involving heavy vehicles) should prompt:

  • Temporary isolation if necessary
  • Engineering inspection
  • Consideration of partial or full barrier removal for assessment

Relationship to Routine Servicing

Post-collision inspections do not replace scheduled servicing.

They should be considered event-driven maintenance, complementing:

• Routine inspections
• Manufacturer-recommended service intervals
• Periodic major servicing (out-of-ground inspection)

Ignoring post-impact checks risks:

• Progressive degradation
• Hydraulic contamination
• Misaligned deployment
• Reduced stopping capability during a real hostile event

Operational Benefit

From an operational and legal standpoint, post-collision inspections:

• Demonstrate proactive asset management
• Reduce the likelihood of undetected latent failures
• Provide defensible maintenance records
• Support incident investigations and insurance claims

In an HVM environment, impact is not an exception - it is an expected operating condition. Post-collision inspection is therefore not optional best practice, but a logical extension of maintaining an effective hostile vehicle mitigation capability.

Common Misunderstandings

Key Takeaway

HVM systems must be understood, operated, and assessed as defensive security assets, not as convenience access equipment. Automated behaviour that appears abrupt or unsafe is often intentional, standards-aligned, and necessary to achieve effective hostile vehicle mitigation.