SOUND-PROPAGATION AT TUNNEL OPENINGS

In Germany, tunnels are a viable solution to many highway traffic problems, including traffic congestion and topographical constraints. However, the positive effects of incorporating tunnels as solutions to traffic flow problems must be weighed against the possible negative effects of irritating noise escaping from the tunnel portals, since the sound generated inside tunnels does not dissipate but rather reverberates within the structure. The beamed sound energy therefore exits nearly undiminished at the portals in tunnels made of hard, sound-reflecting material. Noise emission levels at tunnel openings can also be increased by other factors, such as a sudden increase in traffic volume, or, if present, a gradient increase at portal ramps which increases the noise emission level from heavy trucks as they accelerate and emerge from the portals. The present investigation outlines various sound level measurement methods and proposes basic solutions to excessive tunnel noise.