As a foundation for the development of a new motor vehicle test approval procedure for noise emission measurements, the different parameters defining the noise levels from passenger cars in urban traffic is discussed. The primary parameters are engine speed, engine load and under certain conditions; the vehicle speed. These parameters are controlled by a number of secondary parameters, which can be categorised into 3 groups: vehicle related, traffic related and driver related parameters. Developing a new test method, the vehicle variables such as power/weight, power/engine displacement and gear system are the most important to consider.Equivalent noise level or sound power level are preferable noise descriptors for a type approval test. A better correlation to noise immission levels in urban traffic is then obtained.