A noise barrier is an exterior structure designed to protect sensitive land users from noise pollution. Noise barriers are the most effective method of mitigating roadway, railway, and industrial noise sources. Effective noise barriers typically reduce noise levels by 10 to 15 decibels (dB), cutting the loudness of traffic noise by as much as one half. For example, a barrier which achieves a 10-dB reduction can reduce the sound level of a typical tractor trailer pass-by to that of an automobile.