CCP 11-13-1995 - Laserfiche WebLink

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, '. barrier treatments, , Figure 2 shows the effectiveness of a ] 0 foot noise barrier located either adjacent to the roadway or at the edge of the right-of-way. Either barrier location would result in approximately an 8 dBA reduction in noise , levels relative to the unmitigated condition. Noise levels adjacent to the roadway would be below the state residential noise standard. Benefits associated with placing a barrier adjacent to the road include noise mitigation for the trail and better access to the trail. However, with the barrier adjacent to the road, , pedestrians on the trail would not be visible from the road which could be a safety concern. With the barrier at the edge ofthe right-of-way, pedestrians on the trail would be visible from the road, however, access to the trail would require periodic breaks in the barrier. , Figure 3 shows the effectiveness of a 4-foot earthen berm adjacent to the road. Such a berm would require approximately 24 feet of right-of-way which would restrict options for a sidewalk. A berm would be less , effective than a I O-foot noise barrier resulting in approximately a 3 dBA reduction relative to the unmitigated condition. Noise levels would be below state standards at the residences adjacent to the road, If barriers are constructed adjacent to the road, it is likely that breaks in the barrier would be required for , driveway access. Such barrier breaks would reduce the effectiveness of the barrier. Figure 3 illustrates how 20-foot break in the noise barrier for driveway access would reduce the effectiveness of the noise barrier. Rather than an 8 dBA reduction associated with the unbroken barrier, a broken barrier would result in , approximately a 6 dBA reduction. The effectiveness of the barrier would be further compromised with additional breaks. ~. A vegetative barrier between the roadway and receiver is often suggested for noise mitigation, While a vegetative barrier can effectively block the line of sight and may offer perceived relief (out of sight, out of mind), actual noise reduction is likely to be minimal. Studies have found that to obtain a 3 dBA reduction , in noise levels, a dense vegetative strip 50-feet wide is required. . As discussed previously, reducing speeds or the percentage of trucks would also result in a reduction in noise I levels, Both of these control measures are difficult to enforce and without enforcement, they would be ineffective in reducing noise levels. l .. . CULTURAL RESOURCES STORM WATER MANAGEMENT I I - ~ . .- - - lIiJi-' *,::t J 48 -~~-