3.13 NOISE

A noise study was conducted for the beltway project. Results of the study are summarized here; more detailed information is provided in the Noise Study Report (Appendix C).

3.13.1 Existing Conditions

The Federal Highway Administration has developed noise abatement criteria based on the A-weighted, equivalent level noise descriptor (L_eq(h)). The L_eq(h) is the equivalent steady state sound level measured in decibels (dBA), and reported over a period of one hour which contains the same acoustic energy as the time-varying traffic sound level during that same hour. Table 3.13 lists the upper limits of the L_eq(h) desirable noise levels that are part of the Noise Abatement Criteria (NAC) established by the FHWA. Any noise levels that approach or exceed these criteria would not be desirable and would be considered a noise impact.

Table 3.13

NOISE ABATEMENT CRITERIA

HOURLY A-WEIGHTED SOUND LEVEL

The majority of the beltway study area lies within rural areas, and the land use is classified as Activity Category "B" or "D". Activity "C" mostly pertains to commercial land use or business offices. Storage buildings or warehouses are not usually considered to be noise sensitive.

Ambient noise levels within the study area are primarily caused by vehicular traffic moving on the existing roadway network. Noise levels for the project area were determined by direct field measurements using a Quest 2800 sound level meter. Noise levels for locations near existing highways were determined by modeling the current traffic volume (1998 traffic data). Noise levels ranged in the mid to upper 40 L_eq(h) dBA level adjacent to unimproved county roads and ranged in the upper 50 L_eq(h) dBA to mid 60 L_eq(h) dBA level near existing highways. Noise levels exceeding the FHWA impact criteria currently occur at several residences located adjacent to N-2 .

3.13.2 Impacts of the Finalist Alternatives

The procedures included in the FHWA Traffic Noise Model involve an analysis of traffic noise in terms of traffic parameters (vehicle type and speed), roadway design and receptor characteristics. These parameters are input into the computer model which provides the noise level estimate. All noise levels referred to in this study are exterior noise levels. Detailed engineering regarding the exact alignment and grade of the beltway alternatives, cut and fill areas, and intersection design is beyond the scope of the current level of the beltway study. As such, the traffic engineer's best estimates of these parameters have been incorporated into the model, therefore, these results must be considered preliminary. Further analysis of the noise impacts and recommended mitigation should be completed using more detailed design information if any of the build alternatives are selected.

In accordance with the Nebraska Department of Roads policy, a noise impact occurs and abatement measures will be considered for receptors in Activity Category B if:

• The predicted future year noise levels approach or exceed NAC criteria (67 dBA or 72 dBA for Activity Category C). Approach is defined by the NDOR as 1 dBA less than the noise abatement criteria or;
• The predicted future year noise level exceeds the existing noise level by 15 dBA or more.

Future Noise along Existing Roadways. Construction of the east beltway alternatives will increase traffic volume on several existing roadways that cross or parallel the beltway alignments (Interim Report No. 3 (WSA, revised 1999)) and which are not necessarily in the beltway study area. Those roadway segments which were predicted to have an increase of 50 percent or greater traffic volume were included in the noise study.

For these locations, the 2030-Build projected traffic Leq(h) noise level at each receptor was compared to the 2020 No-Build traffic Leq(h) noise level to determine future noise impacts for receptors adjacent to the existing roadways. This analysis indicated that noise levels will generally increase, however, no noise impacts were predicted (see Appendix C, Tables C.4 to C.11).

Future Noise along the Beltway. The beltway noise analysis included all receptors within approximately 240 m (800 ft) of the edge of pavement (within the 300 m (1000 ft) range of accuracy of the model). The results of the noise analysis for all of the receptors analyzed are provided in Appendix C, Tables C.12 to C.17. Tables C.12 to C.14 are the SM-4 alternative with the varying traffic volumes depending on connection with the three different east alternatives. Although traffic volumes are somewhat different, the noise impacts are the same at the receptor sites. Tables C.15 to C.17 are the three east beltway alternatives.

Receptors which are predicted to have a noise impact are listed in Table 3.14. There are 7 impacted receptors along SM-4; 14 along EC-1, 9 along EM-1; and 13 along EF-1.

Table 3.14

RECEPTORS IMPACTED BY NOISE

The area adjacent to the roadway which will be within the 66 dBA contour will vary depending on traffic volume and type, and topography. This contour was estimated based on review of the predicted noise levels for the existing receptors along the alignments, and by inserting additional receptors. Along SM-4 the contour ranges from 52 to 76 m (170 to 250 ft) from the edge of pavement; along EC-1 and EM-1 the contour ranges from 46 to 58 m (150 to 190 ft); and along EF-1 the contour is approximately 46 m (150 ft) from the edge of pavement. These distances will increase near the major intersections. Based on this evaluation, the 66 dBA contour would extend no more than 30 m (100 ft) beyond the edge of the right-of-way, under the worst case scenario; and in some cases, would not extend beyond the right-of-way at all.

Noise was modeled at the three historic properties that occur within 240 m (800 ft) of the edge of pavement of the road (Table 3.15). None of these sites were predicted to have noise impacts (noise impacts generally occur within 75 m (250 ft) of the edge of pavement. None of the other historic standing structures were within 300 m (1,000 ft) of the edge of right-of-way; therefore, they were not modeled.

3.13.3 Proposed Mitigation

In accordance with the NDOR Noise Abatement Policy, noise abatement measures must be considered where predicted traffic noise levels approach or exceed the noise abatement criteria, or when the predicted traffic noise levels substantially exceed the existing noise levels (i.e. 15 L_eq(h) dBA). Two types of noise mitigation measures were considered during this study: shifting the roadway alignment horizontally and constructing noise barriers.

Shifting the Roadway Alignment Horizontally. A shift in the horizontal alignment can sometimes be made to reduce traffic noise where receptors are typically on one side of the roadway alignment and the topography is acceptable. Since sound intensity decreases with distance, shifting the roadway away from the receptor will reduce noise levels.

Constructing Noise Barriers. A noise barrier, either a wall made of concrete or wood products or an earthen berm, may be constructed to break the line-of-sight to the receptor. To be effective, a noise barrier must be continuous and have substantial length and height. In accordance with the NDOR Policy, a noise barrier must be feasible from an engineering standpoint and reasonable from a cost, effectiveness, and access standpoint to be considered.

The feasibility of implementing these types of noise abatement measures was analyzed for the 43 impacted locations. The conclusions of the feasibility study are summarized in Table 3.16. It should be noted that some locations have feasibility for alignment shifts and/or barriers.

Because noise barriers for 13 locations appear to be feasible based on the current alignments, a reasonableness test was conducted for each of these locations. Reasonableness is judged on a point system (see Appendix C). Barriers with a point total of 9 or less are judged to be not reasonable and are excluded from further consideration.

The preliminary evaluation indicates noise abatement measures should be considered at 14 locations (16 receptors) as described in Table 3.17. All proposed barriers provide an insertion loss of a least 5 dBA below the predicted level. Roadway alignment shifts provide a reduction in the predicted traffic noise level increase to less than 15 dBA over existing; however, in most cases only a 1 to 2 dBA reduction is gained.

NOISE ABATEMENT FEASIBILITY

Notes: 1 - Alignment shifted to eliminate noise impact (less than 66dBA or below significant increase of 15 dBa).

2 - Can the exposed height of a barrier be built 4.9 meters (16 feet) or less?

3 - Other noise sources include other roadways that contribute to noise.

There are 27 remaining receptors which are impacted, but for which it appears there are no feasible or reasonable noise abatement measures available. These include 5 on SM-4; 10 on EC-1; 5 on EM-1; and 7 on EF-1. Further evaluation of noise abatement measures should be conducted during final roadway design.

In addition to traffic noise, the project area would experience temporary noise increase during construction. Construction noise levels are typically a function of the scale of the project, the phase of construction, the condition of the equipment and its operating cycles, and the number of construction equipment units operating simultaneously. Measures that may be employed to reduce objectionable construction noise include designating haul routes away from sensitive receptors, controlling noise at the source, and limiting construction activities to certain hours of the day.

3.13.4 No Build Alternative

Under the no build alternative, traffic will continue to increase in the future; thereby increasing noise levels especially as unpaved roads are paved and/or widened with the planned roadway network improvements. However, the No Build alternative would not cause any noise impacts above NAC levels other than at the receptors already exceeding criteria levels under existing traffic conditions.