Austroads Road Design Guide
The Austroads Guide to Road Design Part 6: Roadside Design, Safety and Barriers, provides guidance on roadside design and in particular guidance on evaluating the risk of a roadside and the selection and use of road safety barrier systems.Â
The guide provides information to enable designers to understand the principles that lead to the design of safer roads, identify hazards, undertake a risk assessment process of roadside hazards, establish the need for treatment of hazards and determine the most appropriate treatment. Methods of evaluating the effectiveness of treatment options are summarised. A comprehensive design process is provided for the selection of a suitable roadside barrier and for the lateral and longitudinal placement of barrier systems.Â
About Austroads
Austroads is the peak organisation of Australasian road transport and traffic agencies and is governed by a Board consisting of senior executive representatives from each of its eleven member organisations:Â
- Transport for NSWÂ
- Department of Transport VictoriaÂ
- Queensland Department of Transport and Main RoadsÂ
- Main Roads Western AustraliaÂ
- Department for Infrastructure and Transport South AustraliaÂ
- Department of State Growth TasmaniaÂ
- Department of Infrastructure, Planning and Logistics Northern TerritoryÂ
- Transport Canberra and City Services Directorate, Australian Capital TerritoryÂ
- Department of Infrastructure, Transport, Regional Development and CommunicationsÂ
- Australian Local Government AssociationÂ
- Waka Kotahi NZ Transport Agency.Â
Frequently Asked Questions
What is the purpose of the Austroads Road Design Guide?
The collective purpose of the Austroads Road Design Guide is to promote a uniform approach to roadside design and safety by road agencies through Australia and New Zealand. The Guide provides road design and road safety practitioners with an understanding of roadside safety issues including the assessment of risk and guidance on the design of the roadside and infrastructure that must be accommodated within the road reservation.Â
What are the road design principals to achieve the safest system?
Road and roadside designers should consider the safety of all road users and produce a road environment that promotes safer travel, design for risk reduction, and choose appropriate barriers and other treatments for potential impacts at the site.Â
What is the Roadside Risk Assessment Process?
The target level of risk is termed the Network Roadside Risk Intervention Threshold (NRRIT) and is set by a jurisdiction for a network independently of project requirements. The NRRIT evaluates the collective risk of run-off-the-road crashes on the roadside using an assessment of Exposure, Likelihood and Severity. If the NRRIT for the project site exceeds the values established by the state road agency then the hierarchy of control is to first remove the hazard, then treat the hazard that may result in a crash or contribute to the severity of a crash, and finally to install a safety barrier to shield the hazard. Safer roadsides often involve the installation of a safety barrier.Â
What are some examples of significant hazards?
Significant hazards include oncoming traffic, tree lined edges, utility poles, fixed base lighting columns, rock cuttings, exposed culvert headwalls and steep embankments.Â
What are some of the key factors that may contribute to run-off-road crashes?
Key factors that may contribute to run-off-road crashes are road geometry, traffic volume and speed, driver inattentiveness or fatigue, road surface condition and weather.Â
What is the shy-line offset?
Generally, there should be uniform clearance between traffic and roadside features, particularly in urban areas where there are many roadside features. Uniform alignment enhances road safety by providing the driver with a certain level of expectation, thus reducing driver concern for and reaction to the roadside features. The distance from the edge of the traffic lane beyond which a roadside feature will not be perceived as an obstacle and result in motorists reducing speed or changing lanes on the road is called the shy-line offset.Â
What is the benefit of flaring the safety barrier system?
Motorists are less likely to perceive roadside barriers to be a hazard if the barrier is introduced gradually to the roadside environment through the use of a ‘flare’. Flaring should be used to locate a barrier terminal further from the travelled path, minimise shy-line effects where a hazard is close to the travelled path, or provide a gradual transition to a major hazard close to the roadway such as a bridge parapet.Â
In addition to safety barriers, what are some other road design options?
Road design aims to achieve the best practical safety outcomes, using practical and economic measures to mitigate the severity and likelihood of hazardous incidents. In addition to safety barriers designers may also consider audio tactile line marking and reduced speed limits.Â
What is a frangible pole?
Frangible poles are designed to deform upon vehicle impact and are usually used for road lighting as the lighting needs to be close to the road. Types of frangible poles include:Â
- slip-base poles that breakaway at the base upon impact, allowing the vehicle to pass beneath the pole in order to minimise or avoid injury to vehicle occupants.Â
- impact-absorbing poles that collapse over the colliding vehicle and are designed to bring the vehicle to a controlled stop at the base of the pole. These deformable poles are designed to remain in the ground after being impacted.Â
What are the recommended treatment options for trees?
Trees feature prominently as hazards in run-off-road crashes and account for a large proportion of fatalities. Trees are a particular hazard when located within and close to curves. Trees create a hazard when they drop branches that can end up on the shoulder or road. It is recommended that trees greater than 70 to 100 mm diameter be removed or shielded with the installation of a road safety barrier.Â
