The Future of Roads - Crash Barriers

Barriers - MAT Foundry

When travelling on Britain’s motorways one of the most prominent features of the journey are the crash barriers lining the way. These steel constructions are designed to prevent vehicles leaving the road in the event of an incident, while dissipating some of the impact energy.

Vehicles leaving roadways, particularly at high speeds, are extremely dangerous and represent a threat to life for not only those travelling in the vehicle, but to anyone in the vicinity too.

A two-tonne lump of metal travelling at 70mph is going damage or destroy almost anything it contacts, including buildings, which is why such effort is taken to contain vehicles in the event of this happening.

Steel rails have been favoured in the UK for a long time, working on the principle of using flexibility to dissipate the kinetic energy from a collision.

The rail itself is extremely strong, but the posts they are attached to are relatively flimsy. This allows for the posts to move, flex or even for the rail to break free in a collision and cushion the vehicle - slowing it down while not catapulting it back across the roadway.

Crash Barrier - MAT Foundry

The most familiar barriers of this type you will recognise will be the almost ever present ‘W’ (or Armco) barrier, and the box beam guide rail.

The ‘W’ barrier is typically used as a roadside barrier to line the outer edges of motorways, or used more selectively to screen roadside hazards or high risk corners.

The box beam style guide rails are often used in more specific circumstances, such as on bridges, and particularly for median barriers as it is able to properly function when impacted from either side.

This is a particular problem on UK motorways which do not have much median space – hence the need for a single rail able to protect both sides of the roadway while still preventing crossover head on collisions.

However, better understanding of how barriers function and their prevention of, and even contribution to, fatal traffic accidents has lead to questions being raised as to the suitability of steel traffic barriers.

One type of steel rail, the cable barrier, is already banned under EU law for its poor performance in impacts involving motorcyclists, leading to severe injuries. Critics of this ban cite evidence suggesting all steel barriers perform badly in these circumstances, but that’s hardly an incentive to allow the use of them.

That poor performance is one of the many reasons why the majority of Europe has used concrete barriers for quite some time - and the UK is lagging behind when it comes to implementing them.

There are a considerable number of reasons for choosing concrete barriers over flexible steel ones, despite the increased likelihood of deflecting vehicles back into oncoming traffic:

Rigid design needs less space, suitable for the UK/Europe’s narrower roads.
More effective against heavier vehicles.
Reduced damage suffered by vehicles colliding with them.
Eliminates headlight dazzling as there are no gaps for light to shine through.
Single barrier can perform all functions, including single barrier medians.
Smooth, flush surface less likely to cause injury to motorcyclists.
More resistant to damage from impacts, requiring less repair and maintenance – significantly reducing the amount of time work crews need to spend at risk on the road.
Drastically reduces instances of needing to close road sections awaiting barrier replacement after collisions, cutting down on traffic delays.

So significant are these reasons that is has been recommended for the UK’s steel barriers be replaced with concrete ones as a matter of urgency, not only just when steel barriers reach the end of their life.

But it may not be the end of the steel barrier just yet, or at least a barrier that uses steel in it’s construction.

The roller barrier is the invention of a Korean firm that upgrades the traditional steel barrier with plastic rollers to reduce the severity of a collision. The rotation of these plastic drums under impact has been proven to have a variety of benefits.

These benefits over a traditional steel guide rail are listed as being:

Reduced damage to both guide rail and vehicle during a collision.
Better impact energy absorption through rotating rollers.
Barrier does not require a deformation space to accommodate flexing.
Rollers guide vehicles with the flow of traffic and don’t deflect them.
Independent parts enable quicker repair and replacement.
Narrower construction requires less space.
Suitable for both roadside and median barriers.
Highly visible with reflective strips, combining functions of hazard warnings.

Overall the roller barrier is far superior to a normal steel barrier and this has led to it being trialled by numerous countries around the world, including the US and Australia.

But even the roller barrier isn’t perfect. The barrier still suffers the same inherent problems a steel barrier does, in that it is severely damaged after impacts and requires the barrier be repaired/replaced – along with the all issues that represents.

Cost is also a factor, as replacing damaged sections is still a necessity like the current steel barriers. Concrete barriers are by far the cheapest form of barrier and offer widest array of benefits for that cost, reaching a level of efficiency that's hard to match.

Still playing catch-up, the UK is only part way through replacing its steel barriers with concrete ones, but the flaws between the new roller barrier and traditional steel barriers are likely to be too similar for it to be considered as a viable alternative.

Maybe some circumstances where the roller barrier might be of use exist on UK roads, but for now we’ll be relying on solid concrete rather than flexible steel if the worst should happen while driving.