| MASH08 manual replaces the NCHRP Report 350 |
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| Written by Paul Hansen | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
At Last a Level Playing FieldFrom the 1 January 2009 the MASH08 manual (Manual for Assessing Highway Safety Features) replaces the NCHRP Report 350 (Recommended Procedures for the Safety Performance Evaluation of Highway Features) in the USA. The effects of this change in standard will affect road safety in Australia. The adoption of NCHRP350 as a standard came about in 1991 after Act of Congress making it mandatory for all states in the USA to have uniform and common safety standards for highway features. FHWA (Federal Highway Administration) had commissioned Report 350 at the same time and used this Report 350 as the “ready made” standard to meet Congress’s demands. It happened that Report 350 was based on research involving the 2000kg pick-up truck, and hence this vehicle became the standard vehicle for testing in the new system. Thus mandatory testing of safety hardware came into force in 1993 with a 5 year window for mandatory installation of NCHRP350 tested articles. Thus all highway safety features installed from 1998 in the USA had to be NCHRP350 compliant. When AS3845 was completed in 1999 it adopted the NCHRP350 test requirements as the basis for that new Australian standard. The review of the NCHRP Report 350 has been in progress many years and the new manual MASH08 comes into force in the USA on 1 January 2011 after a two year transition period. However, all product testing commenced after 1 January 2009 has to be to the new MASH08 standard. Thus products tested to the new MASH08 standard will start coming on line in Australia in the next few of years. So what is new and what has not changed? In the space available in this article I just want to comment on two significant changes. Firstly MASH08 seeks to redress a glaring absence in engineering logic concerning the testing of wire rope safety fences. The British Standard TD32/89 (published in 1989) forced manufacturers to test over lengths of 600 metres. It is well known that the shorter the length of WRSF (wire rope safety fence) that is tested the better is the performance. However, neither of the two great standards published in the 1990’s (being the American NCHRP350 and the European EN1317) thought to specify the test length for wire rope safety fences. Brifen has consistently put an argument in the last decade that authorities should set a minimum test length standard of around 250m to 300m to attempt to reduce the influence of the impact load being absorbed at the anchor and thus giving a better indication of the true deflection of the fence. Clearly the shorter the fence the lower is the deflection result and that is why all WRSF other than Brifen have been exclusively tested in the range 60m to 120m fence length. Testing at short lengths not only has the benefit of minimising deflection but more importantly of “hiding” deficiencies in the all important post-rope interaction process. A couple of years ago a manufacturer went to the UK determined to enter that marketplace and did the required 600m test length impact test. The car went through the ropes and carried on. The test passed over 100m but was exposed over 600m fence length. Not wanting to damage the home market they quietly left England never to return. MASH08 has not adopted Brifen’s recommendations but it has set a minimum test length of 600 feet (183 metres). If nothing else this a practical recognition that the performance of the test article depends on the standard of construction of that article, not just on the impact energy it is being subjected to. Which brings me to the second point, the impact energy levels are changing. These changes reflect the increase size of vehicles in the last 20 years, and in the case of the TL4 test level, the correction of an anomaly in NCHRP350. The following table highlights some of the important changes in vehicle sizes that will interest Australian authorities.
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| Last Updated ( Sunday, 17 August 2008 ) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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