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When is MDOT required to do a traffic noise analysis?
- MDOT is required to do a noise analysis on any highway project that may significantly increase noise impacts on the adjacent properties. MDOT follows federal regulation 23 CFR 772 and State Transportation Commission's Noise Abatement Policy #10136 as to when traffic noise impact and abatement analyses are required.
- MDOT is required to do a noise impact and abatement analysis for all Type I and Type II Federal-aid projects.
- A Type I project is, as stated in 23 CFR 772.5:
- The construction of a highway on new location; or,
- The physical alteration of an existing highway where there is either:
- Substantial Horizontal Alteration. A project that halves the distance between the traffic noise source and the closest receptor between the existing condition to the future build condition; or,
- Substantial Vertical Alteration. A project that removes shielding therefore exposing the line-of-sight between the receptor and the traffic noise source. This is done by either altering the vertical alignment of the highway or by altering the topography between the highway traffic noise source and the receptor; or,
- The addition of a through-traffic lane(s). This includes the addition of a through-traffic lane that functions as a HOV lane, High-Occupancy Toll (HOT) lane, bus lane, or truck climbing lane; or,
- The addition of an auxiliary lane, except for when the auxiliary lane is a turn lane; or,
- The addition or relocation of interchange lanes or ramps added to a quadrant to complete an existing partial interchange; or,
- Restriping existing pavement for the purpose of adding a through-traffic lane or an auxiliary lane; or,
- The addition of a new or substantial alteration of a weigh station, rest stop, ride-share lot or toll plaza.
- If a project is determined to be a Type I project under this definition then the entire project area as defined in the environmental document is a Type I project.
- A Type II project is the construction of a noise abatement measure along an existing highway. The Type II program is a voluntary Federal-aid noise abatement program in which Michigan participates. A community must fill out an application (found on the MDOT Noise Abatement web page) to qualify for a Type II project consideration. (NOTE: MDOT's Type II program is currently suspended due to budget constraints. Applications are not taken during program suspension.)
- Noise abatement must meet feasibility and reasonableness, the same as with Type I noise abatement, plus:
- Eighty percent of the dwelling units within 500 feet of a limited access highway preceded the highway or the last pre-1994 major capacity improvement.
- Type I noise abatement analysis from a previous study did not find abatement to be unfeasible or unreasonable.
- The government entity in which the abatement will be located must provide 10% of the total construction cost - due at the time of construction.
- MDOT will favor applications from locations where zoning and building regulations are in place to preclude future noise abatement needs along highways.
When does a traffic noise impact occur?
MDOT defines a traffic noise impact:
- As approaching 1 dB(A) (A-weighted decibel) of the FHWA Noise Abatement Criteria (NAC), [for example: for NAC Category B (residential) a design year sound level that is equal to or greater than 66 dB(A) would be considered an impact], or;
- When design year predicted noise level is 10 dB(A) higher than existing.
What are the types of noise abatement?
At minimum, a noise barrier (wall or earthen berm) must be considered for noise abatement. The noise barrier tends to be the most practical and cost effective.
Other acceptable noise abatement measures listed under 23 CFR 772.15(c) are:
- Traffic control devices and signing for prohibition of certain vehicles.
- Time use restrictions for certain types of vehicles.
- Modified speed limits.
- Exclusive lane designations.
- Alteration of horizontal and vertical alignments.
- Acquisition of property (predominantly unimproved property) to serve as a buffer zone to preempt noise sensitive development.
- Noise insulation of Activity Category D land use facilities listed in the NAC. Post installation maintenance and operational costs for noise insulation are not eligible for federal-aid funding.
Will vegetation help reduce noise levels?
Planting can provide a visual screen from the highway and likely will improve the perception that noise is less. However, the vegetation would need to be hundreds of feet deep and very thick to receive a true perceivable reduction in traffic noise.
Will a noise barrier be built if the project results in a traffic noise impact?
A noise barrier will be built after a noise abatement analysis determines that the barrier meets warrant; that is, it meets both the feasibility and reasonableness criteria.
What is a benefited unit?
A benefited unit is a location, such as a residence, that directly receives at least a 5 dB(A) reduction because of an abatement measure.
How does MDOT define "feasibility and reasonableness"?
Feasibility is abatement that:
- Can be built while addressing safety and constructability concerns.
- Provides at least a design year traffic noise reduction of 5 dB(A) for 75% of impacted receivers.
Reasonableness is abatement in which:
- The construction cost ($45 per square foot for the single side face surface of barrier) divided by the number of benefiting units is equal to or less than $49,907 (2022) per benefiting unit.
- The majority of benefiting residents and property owners are in favor of the noise barrier.
- Provides a design year traffic noise reduction of 10 dB(A) for at least one benefitted unit and at least a 7 dB(A) reduction for 50% or more of the benefitted units.
Does the public have any input?
Only the residents and property owners of benefitting units of the abatement measure can vote for or against a reasonable and feasible abatement measure.
All residents and property owners whose property abuts the noise abatement measure or has an unobstructed view of it and local governments officials will have input on the aesthetics of the abatement structure.
How are traffic noise complaints handled?
A position in MDOT’s Bureau of Bridges and Structures has primary responsibility for public complaints. MDOT will record and respond to complaints about traffic noise; however, there is not a specific program to address individual public complaints about traffic noise, nor is there a State or Federal program that provides funding in response to public complaints. No noise abatement activities will result. The EPA Office of Noise Abatement and Control once existed to address the issue, but the program's funding was eliminated in 1981.
The Type II program can address those residential areas established before the highway and meet the requirements set in the MDOT noise policy. (Note: MDOT's Type II program was suspended December 2007 and remains suspended.)