ROAD TRAFFIC NOISE IN TUNNELS AND AT TUNNEL ENTRANCES: EFFECT OF NOISE-ABSORBING CLADDING

STRASSENVERKEHRSLAERM IN TUNNELN UND AM TUNNELMUND, WIRKUNG SCHALLABSORBIERENDER AUSKLEIDUNG

THE MOST EFFECTIVE MEANS OF PROVIDING PROTECTION AGAINST ROAD TRAFFIC NOISE IS TO PUT CRITICAL SECTIONS OF ROADS IN TUNNELS. HOWEVER THERE IS A MARKED INCREASE IN NOISE NUISANCE AT TUNNEL ENTRANCES BECAUSE OF THE SUDDEN INCREASE OR DECREASE IN NOISE INTENSITY WHEN A VEHICLE ENTERS OR LEAVES THE TUNNEL AND BECAUSE OF THE MARKEDLY HIGHER ENERGY-EQUIVALENT PERMANENT SOUND LEVEL (TRUMPET EFFECT). THIS NUISANCE IS ESPECIALLY NOTICEABLE IF BUILDING HAS TO BE CARRIED OUT ABOVE THE TUNNEL UP TO THE ENTRANCES. SYSTEMATIC STUDIES ARE TO BE CARRIED OUT TO DETERMINE WHETHER THE ENERGY-EQUIVALENT PERMANENT SOUND LEVEL, THE 1% LEVEL AND THE AVERAGE TRAFFIC NOISE LEVEL FLUCTUATION DEPEND ON THE TUNNEL PARAMETERS LENGTH AND OPEN SURFACE AND ON THE LIGHT AND LEVEL ADAPTATION SECTIONS AT THE TUNNEL ENTRANCES. MEASUREMENTS TAKEN IN EXISTING TUNNELS, SOME OF WHICH HAVE SOUND-ABSORBING CLADDING, WILL SHOW TO WHAT EXTENT A SITUATION CORRESPONDING TO FREE SOUND PROPAGATION CAN BE PRODUCED BY SUCH PROTECTIVE MEASURES.