Motorways in the UK have the lowest number of accidents per mile than any other road. There are several reasons for this, most notably the fact that there is a lower risk of collisions because of barrier systems. Barriers between the carriageways prevent vehicles travelling in opposite directions from coming into contact with each other, preventing potentially fatal head-on collisions. Additional barriers along the edge stop vehicles from leaving the road and colliding with other obstacles and hazards. There are also fewer junctions and no tight corners to worry about so you can drive far more consistently.
Motorway barriers prevent vehicles from leaving the road by absorbing energy from the impact and redirecting the vehicle along the length of the barrier. This is much safer because it removes the risk of colliding with obstacles beside the road or falling down an embankment. When struck the barrier absorbs much of the kinetic energy and stops the vehicle from flipping or re-entering the stream of traffic. This is known as containment and all barriers are extensively tested to ensure they provide the right level of it.
The European Standard EN1317 sets out the requirements for all road restraint systems including the various types of barrier in use in the UK. It was first established in 1998 and is divided into parts to detail the testing and performance requirements of various types of product. Products are tested to determine their performance class, safety level and the amount of space they require for smooth operation. Systems that successfully pass the tests are awarded a CE mark and are safe for use.
On motorways in the UK, barrier products are chosen to ensure containment. There are specialist products designed to maximise this including flexible systems that absorb as much of the impact energy as possible. Barriers on UK motorways need to be tested for high speed impacts to ensure they meet the required criteria. It is also important to test them for various weights because of the large commercial vehicles that use the roads. The best high containment motorway barriers can safely contain vehicles up to 38 tonnes travelling at 40mph. All systems should be chosen to suit the mixture of traffic, the volume, the speed vehicles are travelling at and the risks along the side of the road.
There are several different types of motorway barriers but they fall into two broad categories; flexible or rigid. Flexible barriers are the most common because they provide good levels of containment without putting a great deal of pressure on passengers. Rigid barriers are stronger but impacts are felt much heavier by vehicle users.
In the UK flexible steel beam or wire rope barriers are the most common. These systems were chosen because they are proven to offer containment and also have the lowest effect on vehicle occupants. Flexible systems are still commonly seen along central reservations on motorways but the Highways Agency has changed its policy and recommends rigid concrete systems are used instead. This change is because the risk of vehicles entering a road with traffic travelling the opposite direction has huge potential for causing a large pile-up.
Flexible systems are more cost-effective but require more maintenance to ensure they are kept in the best possible condition. Rigid barriers take longer to install and require much more operating space. With both types the last thing road users want is to see that the systems designed to keep them safe are corroded or in bad condition. When damaged smaller sections of the flexible systems can be replaced, meaning it is easier and cheaper to ensure that the barriers remain strong and meet performance levels. Rigid systems last longer even if they are collided with.
Although only a small number of different systems are used in the UK at present the Highways Agency is open to using new products as and when they successfully meet European Standard EN1317. Unfortunately there are very few alternatives to using some form of barrier for safety due to spatial limitations. In the US carriageways can be separated by 40 feet with a gently sloping ditch between the two. In the UK there is no space for a similar layout so compact motorway barriers are the best option.