Crash barriers are barriers used in road design, and are put in place to prevent vehicles from leaving the roadway and to improve road safety. Crash barriers are commonly seen at sites where it may prove dangerous or even fatal if the vehicle accidentally left the roadway. Typical sites for crash barriers are bridge supports, mountain roads and median separators on multi-lane highways. Crash barriers are designed so that any vehicle hitting the barrier is steered back onto the roadway, and this is sometimes achieved by designing the crash barriers so they break at impact allowing the barrier to deform and deflect the vehicle back onto the road. Motorcycles are vulnerable to crash barriers, and high vehicles such as lorries and vehicles with a high centre of gravity, are vulnerable to going over some crash barriers. Better crash barriers have been developed since the 1990s and these crash barriers can hold up and lead back vehicles of up to 40 tons.