This International Standard is the first stage in the development of a test intended to provide a useful definition of interior noise for engineering and contractual purposes. It specifies the conditions for obtaining reproducible and comparable measurements of the levels of the noise and the noise spectra inside all kinds of motor vehicles intended for road use, including those where the driver and/or passengers occupy an open cabin or even only a well-defined area, but excluding agricultural tractors and field machinery covered by ISO 5131. The results may be used, for example : — to decide whether or not the noise inside the vehicle is in accordance with noise specifications; — to estimate hearing damage risk in conjunction with noise exposure data (see ISO 1999); — to rate the degree of speech interference; — to orient a programme of more elaborate measurements for the purposes of studying noise reduction procedures. The specified procedure is intended neither for the measurement of pressure oscillations at very low frequencies, nor for the assessment of the noise exposure for comfort and security such as fatigue and vigilance. The present state of the art does not yet allow a good correlation between measured data and comfort and security. NOTES 1 The test procedures described in this International Standard are engineering methods as defined in ISO 2204. 2 Measurements may be made on sources emitting noise of an impulsive character with an impulse sound level meter. 3 When repeating a measurement following this International Standard with other vehicles of the same type or on other measuring sites or with other measuring instruments which comply with instruments of type 1 of I EC Publication 651, differences of the order ± 3 dB may be observed in the test results of the A-weighted sound pressure level measurements.