An Armco barrier (also called a corrugated beam barrier or W-beam barrier) is a steel safety barrier used on highways, car parks and industrial sites to prevent vehicles leaving the road or entering hazardous areas. Made from galvanised corrugated steel beams fixed to posts at 4-metre intervals, Armco barriers meet BS EN 1317 vehicle restraint standards.
What is an Armco Barrier? — The Complete UK Guide
Armco barriers are one of the most recognisable pieces of road infrastructure in the UK. The distinctive W-shaped (or sigma-shaped) corrugated steel beam, typically painted silver-grey from its hot-dip galvanising, lines the edges of motorways, A-roads, car park ramps and industrial site roads across the country. But what exactly is an Armco barrier, how does it work, and what are the different types available?
The History of Armco Barriers
The name "Armco" comes from American Rolling Mill Company (ARMCO), a US steel manufacturer that was an early producer of corrugated steel beam barriers in the mid-20th century. The product became so ubiquitous that the brand name became a generic term in the UK, much like Hoover for vacuum cleaners or Velcro for hook-and-loop fasteners. Today, Armco barriers are manufactured by numerous companies worldwide, all producing the same corrugated W-beam profile to international standards.
The design was originally developed in the United States in the 1930s and 1940s as a cost-effective, strong and repairable alternative to concrete barriers. Its adoption in the UK accelerated through the 1960s and 1970s as the motorway network expanded rapidly, creating enormous demand for vehicle restraint systems.
How Does an Armco Barrier Work?
An Armco barrier works through controlled deformation and energy absorption. When a vehicle strikes the barrier, three things happen:
- The beam deflects — the corrugated steel beam bends and deforms, absorbing kinetic energy from the vehicle
- The posts deflect — the steel or wooden posts supporting the beam flex and may partially pull out of the ground, absorbing further energy
- The barrier redirects the vehicle — the curved W-profile shape tends to redirect a vehicle along the line of the barrier rather than allowing it to penetrate through, providing a controlled return to the carriageway
This controlled, progressive failure is deliberately designed. An Armco barrier that bends and absorbs energy in a crash is far safer than one that is so rigid it stops a vehicle instantaneously — the latter would cause far greater deceleration forces on vehicle occupants. The damage to the Armco beam, while requiring replacement, is evidence that the system has worked as intended.
Types of Armco Barrier
Standard W-Beam Armco (N2 Class)
The most common type of Armco used in the UK. The W-beam profile (so-called because its cross-section resembles the letter W) is hot-dip galvanised steel, typically 3mm or 4mm thick. Standard beams are 4.32 metres long and are bolted together end-to-end to create continuous runs of any required length. Posts are typically steel Z-section, I-section or sigma-section profiles driven into the ground or concreted in, spaced at 1.33m or 2.66m centres depending on the barrier class. This achieves the BS EN 1317 performance class N2 — suitable for normal containment applications on roads with up to 80km/h (50mph) design speed.
High-Containment Armco (H1, H2 Class)
For higher-speed roads or where the consequences of vehicle excursion are severe — adjacent to bridges over railways, or above high drops — higher performance classes are required. H1 and H2 class Armco uses heavier gauge steel, closer post spacing, and sometimes a second (double) beam configuration. These achieve containment of heavier vehicles at higher speeds.
Blocked-Out Armco
Standard Armco has the beam directly bolted to the post (or to a short spacer). "Blocked-out" Armco uses a spacer block (or "blockout") between the beam and the post — typically 150mm or 300mm — which improves the barrier's performance by preventing vehicles from "vaulting" over the top of the beam by snagging on the post. Blocked-out Armco is increasingly specified on motorways and high-speed roads.
Car Park Armco
Multi-storey car park Armco is typically lighter duty than highway Armco, designed for lower vehicle speeds and to contain cars rather than HGVs. It is commonly used on open-deck ramp edges and perimeter locations in car park structures. Car park Armco must still meet structural requirements, but the performance specification is typically below the BS EN 1317 highway classes.
Temporary Armco
Temporary Armco is used for traffic management during roadworks. It uses the same beam and post configuration but may use shorter posts suitable for driving into existing road surfaces. Temporary Armco is specified in Chapter 8 of the UK Traffic Signs Manual for lane closure and roadworks applications.
Armco Barrier Standards — BS EN 1317
In the UK, vehicle restraint systems including Armco barriers must meet BS EN 1317, the European standard for road restraint systems. This standard specifies test methods for assessing barrier performance and defines containment classes:
- N1 — Normal containment (900kg passenger car at 80km/h)
- N2 — Normal containment (900kg passenger car at 110km/h)
- H1 — High containment (13,000kg bus at 70km/h)
- H2 — High containment (10,000kg HGV at 70km/h)
- H4a/H4b — Very high containment (30,000kg tanker at 65km/h)
The appropriate performance class is specified by the highway authority (National Highways, Transport Scotland, TfL or local council) based on the road type, speed limit and risk assessment for the specific location.
Armco Barrier Applications in the UK
Motorways and A-Roads
The UK's 3,900km+ motorway network extensively uses Armco barriers for central reservation separation and edge protection on bridges and elevated sections. National Highways specifies Armco to the requirements of the Design Manual for Roads and Bridges (DMRB) Volume 2, Section 2, Part 8, which references BS EN 1317 performance classes.
Industrial Sites and Warehouses
Armco is widely used in factories, warehouses and distribution centres to protect pedestrian routes, structural columns, rack systems and hazardous areas from forklift truck and heavy vehicle impacts. Industrial Armco applications do not require highway-standard BS EN 1317 certification but should meet the Health and Safety at Work Act 1974 and relevant HSE guidance on workplace traffic management.
Car Parks
Multi-storey car park Armco typically uses lighter sections and shorter posts than highway Armco. It provides vital vehicle restraint on ramp edges and open-deck perimeters where the consequences of vehicle excursion are severe.
Armco Barrier Cost in the UK
The cost of Armco barriers in the UK varies significantly depending on specification, quantity and whether installation is included:
- Supply only — standard N2 class Armco: approximately £35–£60 per metre, including beams, posts and fittings
- Supply and install on private land: approximately £80–£150 per metre, depending on ground conditions and access
- Highway Armco (with lane closure, permits and traffic management): from £200–£400+ per metre depending on scheme complexity
These are indicative figures for 2025 — contact Barriers Co for a specific quote for your Armco requirements.
How Long Do Armco Barriers Last?
Hot-dip galvanised Armco barriers, when properly installed and not severely damaged in impact events, have a design life of 40–50 years in typical UK highway environments. The galvanised zinc coating provides cathodic protection against corrosion. In coastal environments with higher chloride exposure, the design life may be shorter and more frequent inspection is recommended.
After significant impact damage, Armco sections should be replaced — damaged sections do not provide the same energy-absorbing performance as new sections.
Armco Barrier Installation
Armco installation typically involves: site survey and setting out, post driving or boring (depending on ground conditions), beam installation and splicing, end terminal installation, and final inspection and sign-off. On public highways, work requires the appropriate Streetworks permit, traffic management under Chapter 8 of the Traffic Signs Manual, and for National Highways roads, a licence under Section 50 of the New Roads and Street Works Act 1991.
Buy Armco Barriers from Barriers Co
Barriers Co supplies the complete range of Armco barriers for highway, industrial and car park applications. We stock standard N2 class W-beam Armco, H1 and H2 class heavy-duty systems, car park Armco and temporary Armco for roadworks. Supply-only or supply-and-install. UK-wide delivery. Contact us for a free quote.