To be effective in providing road safety at night time, a sign needs to provide a minimum level of reflectivity. However, there is no single minimum value of retroreflectivity that is applicable to all signs. The minimum value is sign specific and depends on (inter alia) the action required of the driver by the sign and the sign placement. The minimum value is best determined by use of a sign model. An example of such a model is `Signlife' developed by ARRB Transport Research in Australia. While it is possible to use these models as sign management systems, an alternative approach is to use these models to define the sign size and placement of standard sign designs. In making this assessment, it is recommended that the reflectivity values used are the aged minimum values as set out in AS 1906.1. This value is selected on the basis of a study into the deterioration of sign reflectivity recently carried out in New Zealand. (A)
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