Road traffic noise in the speed range of 30 - 50 km/h

To revise the Nordic prediction method for road traffic noise, measurements of road traffic noise have been carried out in Denmark and Norway on streets with speeds lower than 50 km/h. Measurement sites have been chosen on both normal thoroughfare streets and also on streets with some kind of traffic regulation measures, eg bumps or narrowings. To complete the measurements and to get measurement data from all Nordic countries, additional measurements have been carried out in Finland and in Sweden in 1994. This report contains the results of the Finnish measurements. Measurements were made at eight measurement sites situated in Helsinki and Espoo. The measurements were carried out by measuring sound pressure levels (in the frequency range of 20 - 20 000 Hz) produced by single vehicles. In addition to sound levels with time-weighting SLOW (Leq and Lmax), the speed of the vehicle was measured with a hand-held radar when the vehicle passed the microphone. On each vehicle it was noticed if the vehicle was driving with uniform speed or if it was accelerating or decelerating. Average results for light vehicles show that, at speeds lower than 50 km/h, speed has an influence on noise levels produced by the vehicle. The dependence is evident even at the site with the lowest average speed. On the other hand, results for heavy vehicles don't have any clear dependence on speed under 50 km/h. At different measurement sites, normalized sound exposure levels (speed 50 km/h, distance 10 m) for passenger cars with uniform speed vary from 72.5 dB to 75.4 dB. The speed correction factor (assuming logarithmic dependence on speed) for passenger cars with uniform speed according to these measurements is 23 which is smaller than the respective value (30) of the Nordic prediction method for speeds over 50 km/h. At two measurement sites, sound exposure levels of accelerating passenger cars were found to be 1.0 - 1.5 dB higher (at 50 km/h) than of decelerating passenger cars.