Further refined version of the proposal (incorporating comments received during the 62nd GRB session) in document GRB/2016/2 intended to update and clarify the regulation. The proposal refines definitions, removes the “AWD” abbeviation for “audible warning device” to avoid confusion with its more common use for “all wheel drive”, adds T category agricultural vehicles to the scope, modifies some administrative communications, and proposes three-direction acoustic measurements. The proposal also aims to structure the regulation to enable its application to additional sound warning devices not presently regulated at the international level, excluding acoustic vehicle alerting systems (AVAS) which will be subject to a separate regulation on minimum vehicle sound levels.