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Debate - Motorway barriers

The debate continues to rage over whether concrete or steel makes the most effective barriers for motorway central reservations.

This week we ask: Do concrete road barriers provide a better option for motorway central reservations?


David Jones, director, Britpave - British In-situ Concrete Paving Association

Every week there are at least two motorway crossover accidents resulting in an annual death toll of around 40 people.

This fact shows that steel barriers are no longer adequate to cope with heavier lorries and growing traffic levels.

Crossovers are among the most serious motorway accidents which, apart from the price in Slipformed concrete barriers offer an effective and long term economic solution to the problem of catastrophic crossover accidents.

human lives, have considerable economic costs. Motorway fatalities cost an estimated £1M each and following a crossover accident, motorways are completely closed for hours, resulting in extensive traffic delays and a hefty bill to replace the failed steel barriers.

Since 1995 slipformed concrete barriers have been installed on sections of several of Britain's busiest motorways including the M1 and M25. Since their installation there have been no reported crossover accidents nor any maintenance required.

The sections all show evidence of vehicular contact but their strength and rigidity has restrained the vehicles from breaching the central reservation. Furthermore, unlike other barrier systems, they do not have to be replaced if a vehicle has collided with them. Concrete barriers are built to last for at least 40 years. The on-going replacement programme for steel barriers underlines their short life span.

In addition to the increased road safety benefits, slipformed concrete barriers allow motorway capacity to be increased without taking up any more land.

Unlike concrete, steel barriers need several metres of central reservation to accommodate deformation if they are hit.

Replacing steel barriers with concrete means that this area could be used for an extra traffic lane without the need for expensive planning inquiries or further land take. This approach has been used successfully on the M25 where three lanes have been increased to four.

Steel barriers and wire fences, like such predecessors as the barriers of rose bushes and thorn trees introduced on the first motorways in the 1960's, are no longer adequate to meet the demands placed upon them.

Slipformed concrete barriers offer an effective and long term economic solution to the problem of catastrophic crossover accidents.


Trevor Mustard, principal engineer, Corus Tubes

Crash barriers have become a standard feature of our roads and motorways over the past 40 years and play a vital role in road safety.

Research identifies a number of key characteristics required of crash barriers for optimal safety, and steel systems have many structural and practical advantages that contribute to satisfying these criteria.

Steel's inherent ductility makes it an excellent material for impact protection. The ability of steel barriers to absorb energy ensures that a vehicle travelling at speed does not come to an abrupt halt. Because the steel barrier system deforms, it significantly lowers the rate of vehicular deceleration, protecting the car and, more importantly, its occupants.

In addition, steel barrier systems are designed to maintain vehicle direction, greatly reducing the risk of overturning, loss of control and potential collision with other vehicles. Design flexibility allows steel barriers to meet the varying vehicle containment requirements efficiently, using the appropriate component combinations.

Steel crash barriers have also been found to have a positive psychological effect on drivers as they provide a sense of openness. Official tests ('Effect of highway divider islands on user driving practice' by Christian Tetard, Proceedings of the 11th Congress of the International Ergonomics Association, Paris, 1991) concluded that drivers subconsciously feel 'walled in' by solid barriers and have a tendency to steer away from them, encroaching on the nearside lane.

Easy and swift installation ensures that disturbance to traffic flow is minimised. Foundation requirements are not as substantial as other systems and barriers are readily available in stock for replacement over a very short timescale. Specialist craneage is not generally required and components are light and easy to handle.

Subsequently, costs for installation and maintenance remain low.

Environmentally, once the steel barrier has come to the end of its useful operating life, the material can be recycled. The wealth of experience and design expertise in steel barrier systems ensures that they will remain at the forefront of road safety technology for the near and distant future.

The ability of steel barriers to absorb energy ensures that a vehicle travelling at speed does not come to an abrupt halt.

The facts

Britain's first motorway, the 13km Preston bypass, opened in 1948. It had no central barrier or lighting and had unpaved hard shoulders.

It later became part of the M6, and has recently been widened to dual four lane with continuous hard shoulders and crash barriers.

Pre-tensioned wire rope barriers are another option for central reservations that supporters say provide a better level of crossover protection than solid barriers lOn average 10 people a day are killed on UK roads, with 3,443 killed in 2001.

The government has a target of reducing deaths and serious injury by 40% by 2010.

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