To ensure that the solution eventually applied to the highway noise problem is as effective as possible, we have been exploring alternatives to the wooden walls that have been built in Connecticut.
Connecticut’s Department of Transportation tells us that it chose the wooden walls because they were among the least costly walls that could be constructed. The walls cost $1-$1.5 million per mile to install (on one side of the highway). However, our research indicates that wooden walls have high maintenance costs.
We have investigated several other sound abatement approaches:
- Trees and other vegetative barriers — Research by independent organizations, particularly the Noise Pollution Clearinghouse, indicates that trees and brush only provide a reduction in sound if the growth is high enough, wide enough, and dense enough. The NPC report notes that “A 200-foot width of dense vegetation can reduce noise by 10 decibels, which cuts in half the loudness of traffic noise.” However, because of the depth and density required, vegetative barriers are not an appropriate solution for Westport, where most houses are too close to the highway to allow room for such a barrier.
- Airport sound barriers — As some airports, large curved steel barriers have been constructed to reduce the sound from jet engines. These barriers are effective, but extremely expensive.
- Plastic barriers filled with recycled tire material — Carsonite International has provided us with information on their modular barriers made with recycled tires. These appear to be a promising solution — we will post more information soon.
In addition to barriers themselves, we have investigated:
- Sound-reducing asphalt — Connecticut already uses a type of asphalt on I-95 that is designed to reduce traffic noise. The The NPC report notes that “While it is true that noise levels do vary with changes in pavements and tires, it is not clear that these variations are significant when compared to the noise from exhausts and engines, especially when there are a large number of trucks on the highway.”Presumably, the noise levels in Westport would be even higher than they currently are if not for the noise-reducing asphalt already being used. We have found no information that suggests that a more effective form of sound-reducing asphalt will be available in the future.
- Speakers that generate sound waves that cancel out the sounds coming from the highway — Engineers we consulted at MIT have explained that sound-canceling systems are available, but would not be cost effective installed along a highway, and would produce deafening conditions for the drivers on the highway.