Well-maintained but older exhausts are not on average noticeably louder than relatively new ones, but there can be large differences in noise levels between different makes of cars. Some police forces use a test based on ISO 5130 to provide supplementary evidence in breaches of Regulation 54 of the Road Vehicles (Construction and Use) Regulations 1986, as amended. The work recommended the method researched by the Transport Research Laboratory (TRL) should replace that used currently by some Police Forces.

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• TRL Report PPR506 - Proposals for in-service exhaust noise testing (PDF - 1852 KB)

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