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Srt calculator user guide SRT Calculator User Guide C F E MAIN ROADS WESTERN AUSTRALIA SRT Calculator User Guide TERNZ Ltd PO Box Ellerslie Auckland New Zealand Phone CTable of Contents Table of Contents i Background Performance Measures and Standards Sta

SRT Calculator User Guide C F E MAIN ROADS WESTERN AUSTRALIA SRT Calculator User Guide TERNZ Ltd PO Box Ellerslie Auckland New Zealand Phone CTable of Contents Table of Contents i Background Performance Measures and Standards Static Roll Threshold SRT Using the SRT Calculator Examples SRT Calculator User Guide CBackground Why prescriptive dimensions and mass regulations are not always enough Heavy vehicle size and weight regulations exist to try to achieve a number of objectives including ? Ensuring a ?t between the vehicle and the infrastructure it will operate on ? Protecting the infrastructure from excessive wear or damage ? Ensuring the vehicle is safe The traditional approach to regulating size and weight has been through prescriptive requirements These have the advantage that they are relatively easy to understand and thus to comply with Equally enforcement is straightforward as only simple apparatus such as a tape measure and weigh scales are needed to check compliance For some aspects of the objectives there is a clear direct link between a prescriptive requirement and the desired outcome For example the maximum height limit of m means that road controlling authorities can design overhead structures on roads with a clearance of m plus some tolerance value and be con ?dent that all legal vehicles will ?t underneath it However for other aspects of the objectives the link between the prescriptive requirements and the desired outcome is less clear cut For example the various vehicle length restrictions on the units making up a combination vehicle in uence the o ?-tracking and hence the lane width requirement on curves and corners but it is not a simple matter to convert from one to the other One of the major safety issues for heavy vehicles is stability and in particular how easy it is to control the vehicle and to avoid rollover Although prescriptive dimensions and mass requirements can be used to promote improved stability there are many factors other than size and weight that in uence stability It is not practical to use prescriptive size and weight limits to ensure stability For example the steady speed rollover stability of a vehicle depends on the centre of gravity height the track width and the compliance in the tyres suspensions and other parts of the vehicle structure If the size and weight limits were set so that all vehicles including those with very compliant suspensions would always have adequate rollover stability this would unnecessarily reduce the load carrying capacity of the better vehicles and signi ?cantly degrade the e ?ciency of the road transport system The solution therefore is to have some measure or measures which quantify the vehicle ? s stability and impose a requirement that vehicles meet some minimum standard for these measures This is the basis of the performance-based standards approach SRT Calculator User Guide CPerformance Measures and Standards What are performance measures and why are they useful A performance measure is a de ?ned quantity that is measured during some standard prescribed manoeuvre