The Concept of Crash Avoidance Space (CAS)

CAS is the space required to avoid or reduce the risk of a crash occurring. As well as being created, CAS must also be maintained and protected. This is a conscious and continuous process that requires both awareness and skill. Heavy vehicle drivers in particular need to have a good understanding of the CAS concept and the various ways it can be applied to enhance road safety.

Drivers are required to continuously scan the road and the traffic environment making subsequent adjustments to speed and position to maintain a safe distance from vehicles and obstacles to the front and the sides.

To create, maintain, and protect CAS, a heavy vehicle driver must:
·       Maintain a four (4) second gap behind the vehicle directly in front increasing the gap in adverse conditions.
·       Stop in a position behind other vehicles allowing sufficient space to steer around the vehicle in front, if necessary.
·       Select a speed that is both within the posted limit and appropriate to road and traffic conditions (which may be less than the posted limit).
·       Maintain a sufficient space to the side from parked vehicles and road side hazards.
·       Vary the position in the lane to provide a buffer from oncoming vehicles and those moving in the same direction.
·       Select a lane in compliance with road law and the prevailing traffic situation, and which is the most appropriate one for the vehicle being driven, to ensure safe turns.
·       Adjust speed to regain CAS in response to changes in road or traffic conditions and speed limits (e.g. when other vehicles cut in or when your vehicle is in another vehicle’s blind spot).
·       Reduce speed in anticipation of the need to stop (e.g. lights ahead which have been green for some time).
·       Approach stationary or slow moving vehicles in front with caution.
·       Drive close to the posted speed limit when safe to do so.
·       Select gaps in traffic which do not encroach on another vehicle’s CAS without slowing traffic flow.
·       Efficiently maintain forward progress by selecting suitable speeds, lanes, and lane positions in relation to forward and adjacent traffic.
·       Be courteous to other road users.
·       Accepts the first safe gap and rejects unsafe gaps.
·       Not give way unnecessarily.
·       Scan continuously to the front and sides looking for hazards. Scanning needs to be performed at short, middle, and long distance ranges.
·       Monitor left and right mirrors for traffic to the sides and rear on a regular basis.
·       Apply low risk driving strategies by reducing speed and covering the brake when a hazard is identified.
·       Increase space to the sides where hazards exist (e.g. parked vehicles or oncoming traffic).
·       Adjust speed and/or position in response to limited vision of the road or traffic environment (e.g. where vision is limited due to other vehicles or objects blocking the line of sight at intersections, blind corners, and crests etc

Why is CAS so important?

Heavy trucks are over-represented in serious road trauma in NSW.
In 2010 heavy trucks:
·       Represented only 2.5 % of registered motor vehicles in NSW
·       Accounted for 7% of all motor vehicle travel in NSW (ABS SMVU 2008)
·       Crashes involving heavy trucks accounted for 17% of all fatalities on NSW roads in 2008, 15% in 2009 and 19% in 2010

The majority of heavy truck crashes involve multiple vehicles, largely either rear enders or other same direction.
Over-representation of pedestrian and head on (not overtaking) impacts for heavy truck fatal crashes.
Other contributing behaviour factors that have a significant influence of crash statistics are: alcohol/drugs, speed, and fatigue.

If all drivers understand and apply the CAS principles, don’t drink/drug drive, keep under the speed limit, and apply fatigue management strategies, I think there is little doubt the roads would be a safer place.

Sources: RMS, NSW Centre for Road Safety, Austroads