15. The expert from CLEPA introduced GRB-56-17 listing further test results of four vehicles performed by his organization on additional sound emission provisions (ASEP) of replacement silencing systems. GRB noted that as an outcome of the test, two possible alternatives were possible to introduce ASEP provisions into UN Regulation No. 59: (i) the test should be carried out back to back to the original equipment and replacement system (ii) the manufacturer of the replacement system should perform the test with the same acceptance criteria as for the original equipment. GRB, in principle, agreed to follow option (ii) and to resume consideration on this subject at its February 2013 session on the basis of a concrete proposal tabled by the expert from CLEPA.