Active Advanced Warnings Signs (AAWS) should be used in advance of traffic signals where sight distance to signals or a potential back-of-queue is limited. They are also used in locations where drivers have a lowered expectation of signals, for example, when driving from a rural to a built-up area. The process to determine the longitudinal placement of AAWS is related to the availability of stopping sight distance and is given in AS1742.14. 

These devices can reduce crashes by up to 35%.

(Austroads 2016)