In instances where a roadside hazard cannot be made safe, removed or relocated, it may be necessary to provide physical protection from the hazard. Safety barriers are available for a variety of applications and this section provides advice on selecting, installing and maintaining safety barriers.
The Australian Standard document “AS/NZS 3845:1999 Road Safety Barrier Systems” discusses various methods of roadside hazard protection and provides direction on the correct use of the different systems. The Standard has been the basis for a number of guidelines written by individual road authorities for use within their jurisdiction.
It should also be noted that the Austroads publication Safety Barriers (1987) is currently being reviewed and updated.Decision to install a safety barrier
Safety barriers are a form of roadside hazard. When considering whether to install a safety barrier, it is important to remember that the barrier will present some danger to the occupants of errant vehicles, and especially to unprotected road users such as motorcyclists. A barrier should only be installed if collision with it will present less of an injury risk to vehicle users and occupants than would result from collision with the roadside hazard that is to be shielded by the barrier.
It is important to consider specifically the danger posed to motorcyclists by both the hazard and the intended safety barrier. As essentially unprotected road users, motorcyclists are particularly vulnerable to unforgiving roadside environments; any obstacle in the path of an errant motorcyclist has the potential to cause severe injury. If it is decided that a safety barrier is necessary at a site, attention should be paid to the design of the barrier to ensure that it poses as little risk as possible to colliding motorcyclists.
The following sections describe a number of roadside safety barriers and end-treatments. This list does not contain all available types of barrier, and the practitioner should be aware that manufacturers continually develop new or improved barrier designs. Accordingly, the information presented here refers to testing procedures, the results of which can be used to determine the suitability of proposed barriers. No barrier should be installed unless it has been shown to meet the applicable standards and can therefore be expected to perform satisfactorily.
Barrier types include rigid barriers, semi-rigid barriers and flexible barriers. Semi-rigid and flexible barriers are preferred as they generally cause less damage to vehicles during a crash, while a rigid barrier is suitable where space is limited and it is placed relatively close to the traffic lane (eg. narrow median).
Where a barrier is essential, the practitioner should bear in mind that barrier posts are the main cause of injury to motorcyclists. Other barrier attributes that are considered to be dangerous to motorcyclists (ATSB 2000) include upper and lower edges (particularly if jagged edges exist), protruding reflectors, low barrier mounting height (as motorcyclists can be thrown over the barrier) and rigid barriers.
Guards have been designed to reduce the severity of motorcycle collisions with barriers. These are available in a range of designs for various types of barrier.