Effects of median barriers on highway noise levels.

Median barriers are widely used on roadways in the United States. The main purpose of this paper was to evaluate a median barrier performance in reducing traffic noise using the latest FHWA Traffic Noise Model, TNM version 2.5. For this study, median barriers were modeled on three different roadway configurations—at grade, depressed, and elevated. The analysis results indicated that the range of insertion loss for a median barrier at grade was less than 1.5 dBA with a barrier height of 2.5 to 10 ft. The range of insertion loss for a median barrier on a depressed roadway (5, 10, and 20 ft below grade) was 0 to 2.8 dBA with a barrier height of 2.5 to 4.5 ft and insertion loss increased up to 4.3 dBA with a taller barrier height of 6 to 10 ft. On an elevated roadway (5, 10, and 20 ft above grade), the range of insertion loss for a median barrier was 0 to 1.7 dBA with a barrier height of 2.5 to 10 ft. Given the results of this research, it is reasonable to conclude that a standard median barrier would not provide a significant level of noise reduction. Furthermore, taller median barriers do not alter this conclusion. When considering the construction of very tall median barriers for noise reduction purposes, the costs would far outweigh the relatively minimal benefits of this approach.