Road Safety Barrier Systems

ROAD SAFETY BARRIER SYSTEMS

ACRS Policy Position

Road safety barrier systems should only be installed at locations where the risk of injury resulting from a crash with the device installed is much less than the risk without the device.

Where installed, road safety barrier systems should be designed such that the severity of any foreseeable crash into the system, or caused by the existence of the system, is reduced to human injury tolerance levels for all road users.

Objective

To improve the intrinsic safety of the road environment and thus reduce the consequences of driver error.

Discussion

The main function of road safety barrier systems is to improve road safety for all road users by reducing the consequences of crashes into potentially hazardous environments. Road safety barriers should shield: vehicles and their occupants, riders, and pedestrians from hazardous objects and other vehicles in the roadside and the median.

Properly designed barriers can and have saved many lives. However, it is becoming increasingly evident from international research and crash investigations that road safety barriers can themselves form serious roadside safety hazards and have the potential to cause serious injury unless they are designed and installed to world's current best practise. For example, some barrier types and designs have been unchanged for decades whereas the vehicle fleet and road usage characteristics have changed significantly.   Similarly, as community attitudes increases demand for safer roads, areas previously considered as (safe) Clear Zones may now in fact be classed as very unsafe roadside areas and hence a safety barrier is required. Installation of a barrier in such situations, while still presenting a certain level of roadside safety hazard, dramatically reduces the risk of injury to the majority of road users.

The scarcity of resources available for roadside protection means that practitioners have to make some hard decisions regarding where road safety barriers are to be provided and what their design should be.

Excursions from the traffic lane will occur.   Alcohol and speed are obvious contributing factors but a large proportion of crashes result from human error:   it has been estimated by Sabey ⁽¹⁾ that up to 95% result wholly or partly from human error.   Similarly, the role of fatigue in crashes, on a spectrum from falling asleep at the wheel through perceptual and decision making errors to reduced attention, is increasingly being recognised as of greater importance than previously considered ⁽²⁾.  

Driver error, fatigue and other contributing factors should not necessarily have death and injury as consequences.   The key to improving safety lies in modifying all aspects of the system, including making the environment more forgiving.   Roadside barrier systems are part of the system and are capable of being modified to improve safety.

The following principals should be adhered to when assessing roadside hazards and/or designing, specifying, and installing road safety barrier systems:

1.       The Swedish 'Vision Zero' philosophy should be adhered to and should act as a filter for any placement or design decisions. This philosophy states:

No foreseeable crash should be so severe that the tolerance of the human body is exceeded causing a long term health loss.

Note that one obvious solution to reducing the consequences of impacting a hazard, e.g. striking a power pole, and complying with the Vision Zero philosophy is to reduce the speed limit and hence speed of impact with the hazard.   However the existence of hazards is only one of the factors involved in setting speed limits and this solution may not be available in all circumstances.

2.       A Road Safety Audit should be carried out preferably at the conceptual design stage for new systems or prior to any major works for existing systems.

3.       Every effort should be made to prevent, render safe, or remove 'unnecessary' roadside safety hazards. Hazardous sites that require treatment should be assessed by independent audit experts, thoroughly documented and ranked for treatment, and progressively addressed as funds become available. Speed limits should be reduced to levels such that if a crash into the hazard occurs, forces are below human injury tolerance levels.

4.       Systematic procedures should be used to review the performance of road safety barrier systems in service and to maintain a readily accessible database with detailed at scene information.

5.       As a minimum requirement, practitioners should become familiar with and apply AS/NZS 3845-1999: Road Safety Barrier Systems, AS/NZS 1742.3-2002: Manual of uniform traffic control devices - Traffic control devices for works on roads, and AS/NZS Road Safety Barrier Manual for Arterial Roads⁽³⁾. However they should also look beyond design standards.

References

(1)    Hirsch, P (1997) Is legal driving safe driving?   www.drivers.com, July 2001

(2)    NRTC (2002) Heavy Vehicle Driver Fatigue:   Review of Regulatory Approach Discussion Paper NRTC and Smithworks Consulting, Melbourne

(3)    Standards Australia, Road Safety Barrier Manual for Arterial Roads, HB 175-2003.