Noise near roads: new approach to assess annual descriptors

Abstract

For green transport one of important aspects is noise abatement. Annual noise metrics become preferable indicators to describe an environmental impact. Developed method to assess annual values is based on the road traffic noise two channel measurements. First microphone is placed near the road centre line and the second microphone in the investigated area for which the annual noise descriptors LDEN and Lnigth will be assessed. Duration of short-term representative measurements always meets important standard ISO 1996-2:2007 requirement to sample at least 30 pass-bys for every vehicle category. As mainly the traffic flow comprises about 10 % of heavy vehicles, total amount of cars recorded during about two hours is enough. Road traffic flow during measurements preferably should be similar as possible to the annual proportion between transport categories. Corrections between measured and annual descriptors are found from statistical processing at the first reference microphone position measured sound exposure levels (SEL) from all transport pass-bys. The histogram of the representative SEL distribution density is recalculated to the annual average day (12 h); evening (4 h) and night (8 h) SEL histograms by taking into account the average whole-day traffic flow data. During measurement time obtained equivalent sound level at the second microphone position in the next data processing step is extrapolated to the annual day, evening and night levels applying obtained corrections. Results of experiments at the distances about up to 50 m from the road centre line shows that assessment with suggested methodology from shot-term measurements are in good conformity with annual value calculations.