The Ministry of Transport administers a suite of regulations that seek to control sound emitted from an individual vehicle.

Amendments to the Land Transport Rule: Vehicle Equipment 2004 (known as Land Transport Rule: Vehicle Equipment Amendment 2007) came into force on 1 June 2008. The amendments tighten-up the subjective noise test procedure for vehicles with modified exhaust systems at Warrant of Fitness inspections. If the vehicle fails a warrant or certificate of fitness for excessive noise the owner has the option to repair the exhaust or to pay for a metered objective test. The amendments to the rule also reduced the decibel limit for new and used vehicles entering the fleet.

In addition to the 2007 Amendment Rule a series of further amendments have been proposed to tackle noisy exhausts. These proposals have been consulted on as part of the normal Rule making process and are expected to be finalised during 2009

Sound emitted from an individual vehicle is normally a transient event and can be assessed against L_AFmax limits. However, sound levels emitted by the combination of vehicles in traffic flows are assessed using L_Aeq (L_Aeq(24h)) as the metric.