The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Bruce Snook by e-mail or on (08) 9323 4634.
To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information herein displayed.
This section provides guidance on the use, selection and location of work zone barriers (also referred to as temporary barriers) that are used in situations where a permanent barrier is inappropriate. Work zone barriers are used in situations where protection is required for a limited time. Examples include:
There are some water filled modules which have not passed crash testing as road safety barriers and these modules are not to be used as safety barriers but can be used as containment fences as defined in AS 1742.3 Manual of Uniform Traffic Control Devices Part 3: Traffic Control for Works on Roads Cl 3.10.1.
The test level for work zone barriers shall be determined based on the speed zone imposed on the work sites. This requirement as well as warrants for the use of various temporary safety barriers is contained within the Main Roads Traffic Management for Works on Roads - Code of Practice.
The principles that apply to permanent barriers are also applicable to the use of work zone barriers. For example, it is recommended that work zone barriers not be installed in proximity to kerbing or where the slope on pavements, shoulders or batters is greater than 1 on 10.
All work zone barriers should be designed to the same requirements, as a permanent barrier in terms of the length required to adequately shield the hazard. Furthermore, when barriers are used at roadwork sites the following issues should be addressed.
Barrier units will act as a safety barrier only if they are properly connected to each other throughout the whole installation. The connections provide barriers with the continuity necessary to ensure that differential movement does not occur at the joints between units, and to resist displacement of the units. Joint movement may cause snagging and pocketing of impacting vehicles.
Work zone barriers must be founded on a base that enables proper alignment and is capable of supporting the barrier and other loads created during impacts. This may be a critical consideration for barriers located adjacent to trenches, deep pavement boxings, foundation excavations, etc.
The minimum length of work zone barrier installed shall not be less than the length of system recommended by distributors and based on successful crash tests. At a particular site the installation must:
It is necessary to provide sufficient space between the barrier and the work area to accommodate the dynamic deflection of the barrier. The deflection of work zone barriers is a function of the speed and type of impacting vehicle, the angle of impact, and the design of the barrier system including its foundation and connections.
Barrier systems should also be located to allow for vehicle roll (also referred to as working width).
Work zone barriers should be installed so that the likely angle of impact is minimised as this will also minimise the dynamic deflection under impact.
The US Federal Highway Administration (FHWA) website (http://www.fhwa.dot.gov/) provides a listing of acceptance letters containing summaries of test results of various temporary barriers and practitioners should utilise this information in considering the design of work zone barrier systems.
The test level criteria for barriers specified in AS 3845:1999 is based on the criteria used in the National Cooperative Highway Research Program (NCHRP) Report 350. It should be noted that the test level criteria were altered in 2009 when the American Association of State Highway and Transportation Officials (AASHTO) released its Manual for Assessing Safety Hardware (MASH). Systems which had been approved to the criteria of NCHRP 350 do not require retesting to the criteria of MASH.
TL3 test results for temporary Type F and New Jersey barriers show that the deflection of barriers ranged from 1.0 m to 2.5 m. The test results contain barrier systems that have several different segment lengths (3.0 m, 3.7 m and 6.0 m). The lengths of the systems tested ranged from about 40 m to 80 m.
Drainage from the uphill side of barriers needs to be provided to avoid ponding against and/or concentrating flows at the ends of the barrier, both of which can create a hazard to road users.
Some temporary barriers allow water to pass beneath or through the barrier.
Monitoring of barriers in the field is the best way to determine the performance of a barrier under particular situations. These observations and feedback by maintenance contractors and staff will identify any problems that may occur with the system, and should ensure optimal performance for future installations.
There are steel work zone systems available and advantages of these may be seen as:
The ends of work zone barriers must be appropriately treated as they can be a major hazard to road users if struck end on.
The most appropriate crashworthy end treatment for a barrier should be selected following consideration of:
Approved road safety barrier terminals for work zones can be found in the
List of Approved Barrier Systems. Attached to this list are design sheets for each product approved which gives guidance on the use of it and the configuration that it is to be used in.