Environment, test procedure, instrumentation and data analyses for comparing interior sound level of multipurpose vehicles, passenger cars, and light trucks having a gross vehicle weight rating (GVWR) of 4540 kg (10 000 lb) or less are established. To obtain vehicle interior sound measurement during road load operation over various road surfaces at specified constant speeds the test method is characterized by having fixed initial conditions (specified initial vehicle speed and gear selection at the starting point on the test site). The measurement data collected is useful for vehicle engineering development and analysis. The test include using different road speeds and various road surfaces as desired.