Extensive roadside noise measurements of 20 000 vehicles in 100 measurement sites in the high-rise city, Hong Kong, are reported. The vehicles are classified into petrol-powered saloon, diesel-powered saloon, mini-bus and small lorry, and bus and big lorry. The survey was mainly concentrated in the urban areas. However, rural areas were also included in the investigation such that comparison with the urban areas could be made. The results obtained illustrate the effect of enclosed environment on the noise emitted by the vehicles and support the simple classification of the sites into closed, semi-closed and open environments. Distinct differences in the sound pressure levels observed in these environments have been found.