Concrete Step Barrier (CSB) is a vehicle restraint system designed to contain vehicles, save lives, reduce congestion and be maintenance free for at least 50 years.
Tested extensively to the requirements of the European Safety barrier standard EN 1317, CSB has the ability to contain errant 4x4s, light vans and trucks up to 13.5 tonnes, including most buses and coaches. CSB has a unique stepped profile that has been shown, through testing and computer simulation, to help reduce injury to occupants of small cars by limiting contact to the base of the barrier and the vehicles’ tyres.
Highways England and CSB
Highways England continuously aims to improve safety and congestion, as well as reduce costs and improve reliability. The use of high containment concrete barriers in the central reserve on highly trafficked motorways is one initiative that helps meet these aims.
With effect from January 2005, and based primarily on safety and cost grounds, the Agency’s policy, as detailed in Volume 2 of its Design Manual for Roads and Bridges is that all new motorway schemes are to use high containment concrete barriers (namely CSB) in the central reserve. All existing motorways will introduce concrete barriers into the central reserve as part of ongoing upgrades and through replacement as and when existing systems have reached the end of their useful life. The extensive Smart Motorway programme of works by Highways England has Concrete Step Barrier as a key element.
CSB inherently provides high containment at no additional cost, delivering a safe environment for motorists. Appropriate containment levels are determined by Government policy and are related to numerous criteria including (but not limited to) the type of road, volume of vehicles and structures being protected. When crash tested, it is important that Acceleration Severity Index (ASI) values meet EN 1317 requirements so that the system used cannot be considered to pose an excessive risk to the occupant of the vehicle hitting the barrier. CSB provides high-level H2 containment with a reduced ASI value of only 1.4 and impact severity level B, which easily meets BS EN1317 requirements.
Experience in other countries and 10 years of use along the M25 in the UK has proved that concrete barrier is safer than competing systems.
Step barrier is specifically designed to limit minor vehicle contact to the base of the barrier and the vehicle tyres. Such slight impact will, in most cases, allow the vehicle to continue on its journey undamaged. Vehicle crash tests approved by the then government's Highways Agency (now Highways England) demonstrate that it can successfully contain all vehicles including 4x4s, pickup trucks and light vans up to 13.5 tonnes, which includes most buses and coaches.
Results from both crash testing and computer simulations – undertaken by the Vehicle Design Group at Arup, one of the world's leading consulting engineers – confirm CSB’s excellent safety credentials. In crash simulation tests, for instance, a series of measurements are taken from a EuroSID dummy and compared to limits set out in ECE Regulation 95 for Lateral Collision Protection. With injuries predicted for CSB being very much lower than set limits, injuries resulting from an impact with CSB are very unlikely to be serious.
Importantly, accidents to workers and to vehicles in road works should also be reduced. As concrete step barrier requires no maintenance, the need for lane closures is reduced significantly. This also increases safety for repair teams who are currently at risk working alongside dangerous moving traffic.
Concrete step barrier requires minimal maintenance and repair throughout its minimum 50-year life as it suffers negligible damage if struck by a vehicle. This means there is often no need to report minor impacts or close off adjacent lanes to carry out repairs. To put this into perspective, at the time that CSB was adopted the then Highways Agency Area 5, which includes the M25 and associated link roads, carried out hundreds of repairs to steel barrier every month at an average cost of around £5M per annum.
With almost no maintenance requirements, no lane closures and no associated delays, concrete step barrier delivers greater journey reliability. This means that all road users will be able to plan ahead and predict journey times with more confidence and accuracy. This better service to users is at the heart of Highways England corporate policy.
CSB is completely maintenance-free, saving clients and taxpayers tens of millions of pounds every year. Even following severe impacts, the barrier is undamaged and requires no repair. By virtually eliminating crossover incidents, the step barrier will save millions of pounds in accident recovery costs and insurance claims.
Maintenance-free means reduced lane closures and traffic congestion that can last more than a single day. The hidden cost of lanes out of service is massive and is increasing with saturation of vehicles on the road system. The construction of CSB is and will continue to make a real contribution towards the free flow of traffic and more reliable journeys for all road users.
In terms of construction costs, three independent studies undertaken by Arup in 2007 to compare various barrier systems confirm that CSB is an exceptionally competitive product. Assuming typical road layouts, findings proved CSB to be cost competitive when considering both basic barrier construction costs and the influence of different central reserve layouts and lighting column options.
With a minimum working life (50 years) double that of competing systems, concrete step barrier will save millions of pounds in replacement costs alone.
CSB eliminates crossover accidents and significantly reduces maintenance requirements. Indeed, a survey on the M25 undertaken by TRL Ltd showed that there were 70 per cent fewer reported accidents alongside concrete barrier compared to competing systems. This has an extremely positive effect on the free flow of traffic as there will be no lane closures, delays, tailbacks or traffic jams, nor the associated costs to British businesses, not to mention the stress and irritation this can cause to motorists.
In contrast to CSB, which is specifically designed to last for at least 50 years, competing systems need to be replaced completely every 20 years. This is an enormous operation, which can create massive delays and traffic congestion for considerable periods of time.
Installed by a single machine served by concrete mixers, barrier construction is rapid and can be undertaken within single lane closures or when planned road surface repairs are undertaken, which again means less congestion for motorists.
In keeping with 2008 Government construction targets, CSB provides an innovative, buildable, fit–for-purpose, resource- and carbon-efficient, resilient and adaptable road safety solution that impacts positively on the whole-life cycle sustainability of the infrastructure assets that it serves.
Key sustainability benefits include:
- 80 per cent less embodied CO2 than competing systems
- Minimum material usage and waste
- Non-polluting in service
- Fully recyclable
- Virtually maintenance-free over a minimum 50 year design life
- Reduces traffic congestion and associated emissions
- Enhances road user and worker safety
For more information on safety barriers, see the Britpave website at www.britpave.org.uk