Monday, June 6, 2011

Listen Up: ADOT works to minimize noise impacts

Concrete noise walls reduce traffic noise by blocking the
path that sound waves travel from the traffic to the residential area.
Most people don’t find the sound of traffic especially soothing …

ADOT certainly recognizes this and is constantly working to minimize the impacts to surrounding neighborhoods from the noise of new freeways.

You would think figuring out the impact of noise could get tricky because everyone perceives it differently – a sound that’s irritating to you might be tolerable to someone else.

But, federal law requires that ADOT estimate the future noise levels from new freeway projects, and if traffic noise approaches or exceeds 67 decibels, noise abatement must be considered. ADOT has taken it a step further, though, and considers 64 decibels to be the acceptable threshold to consider noise abatement for new projects.

The amount by which noise levels will change in a residential area also is a factor. A road project that will cause noise levels to increase by 15 decibels or more is considered an impact and noise abatement measures must be considered.

Just to give you an idea of what a decibel measurement means … a whisper could register at about 20 decibels, normal conversation comes in around 60 decibels and if you were standing about 15 feet from a loud rock band, you’d be hearing sounds measuring roughly 130 decibels.

Now you might be asking – how do you figure how noisy a new road will be before it’s even built?

Well, experts from ADOT’s Environmental Planning Group use sound pressure level meters to take readings of current noise levels in several areas near a proposed project site.

Measurements aren’t taken during rush hour because traffic is typically a little slower and quieter. Measurements are instead taken at the peak traffic noise hour, when traffic is free-flowing and cars are able to drive the speed limit, but the road is at maximum capacity.

Those measurements and the area’s topographic and weather information are plugged in to a very sophisticated computer program. It creates a model of the area and can tell ADOT what noise levels to expect if a new freeway is built, or an existing freeway is widened.

If it is determined a project will cause a noise impact to the area, ADOT has a few options, including:
  • Install noise walls or berms
  • Implement traffic control measures (speed limits, etc.)
  • Modify the proposed freeway alignment
On top of everything, the abatement method chosen has to meet multiple criteria showing that it is reasonable and feasible … a noise wall isn’t reasonable if the residents of the neighborhood don’t want it or it is cost prohibitive and it isn’t feasible if it won’t effectively reduce noise levels.

A little more on noise walls …
Barriers, such as concrete noise walls, reduce traffic noise by blocking the path that sound waves travel from the traffic to the residential area.

When sound waves hit the noise wall, they must bend over and around it. This is known as diffraction, which absorbs the sound energy, thereby reducing noise. For every decibel of reduction, it is necessary to increase the height of the wall by two feet. Noise walls are most effective when the distance between the source and the receiver is no more than 400-500 feet.

ADOT and the Federal Highway Administration (FHWA) are currently studying the use of rubberized asphalt or “quiet pavement,” which can noticeably reduce traffic noise levels. When ADOT/FHWA completes the study, the results will determine whether quiet pavement can be used for noise abatement.

While no analysis, wall or special pavement can completely eliminate traffic noise, ADOT does have one of the most progressive noise abatement policies in the nation and that is something the citizens of Arizona may find soothing.


  1. Sun City Grand resident (approx 1 block from 303 at Clearview Blvd overpass).
    The 303 project appears to be a rape of most of the residents of SCG (those close to the 303). Property values will be driven down. I would like to sue AZDOT, but apparently this is not an option. Seems the only course of action available to me is to plead that every possible means of noise abatement be used on the portion of the 303 that passes through our community. This includes sound supression walls, ruberized asphalt, speed limits, etc.
    I find very little comfort in knowing AZDOT will "consider" noise abatement for noise estimates above 64 dbs. If I sound bitter, how would you feel if you made a major investment in a retirement home and then found out a major highway was being built 1 block from your home?

    1. In ADOT's defense, this freeway isn't a new project. Its been planned for decades and you should have done your research when you purchased your "major investment." This is especially true when the road is clearly labeled Loop 303 and the other two loops in the valley are major freeways. I knew this was the plan for the route and I don't even live close enough for it to remotely affect me.

  2. Is any noise abatement planned for the section of 303 already completed that skirts the northern edge of Sun City West and Corte Bella? The traffic noise is definitely noticeable in these communities, and the small wall already in place doesn't mitigate the sound.

    1. Thanks for your question!

      Improvements to Loop 303 are identified in the Maricopa Association of Governments’ (MAG) Regional Transportation Plan. As this region's metropolitan planning organization, MAG establishes the priorities for funding projects in Maricopa County and along the Loop 303.

      As the implementer of the MAG Regional Transportation Plan Freeway Program, ADOT is working to deliver several projects along the Loop 303 between I-17 and I-10.

      Specific to the Loop 303 and segments north of US 60 near Sun City West and Corte Bella, ADOT has conducted noise studies and determined that noise mitigation will be warranted (based on preliminary noise analysis) when the new freeway is built.

      Recently, MAG needed to rebalance the Regional Transportation Plan and the region (MAG members / cities and towns) approved shifting funding to other facilities within the region to deliver the region’s most immediate needs.

      With that, there is no funding identified in the current Regional Transportation Plan to improve this segment of Loop 303 between US 60 (Grand Avenue) and I-17. If revenue forecasts change and sales tax money collections become more positive, this could change.

      For more information on Regional Transportation Plan projects and when they are prioritized, please visit the MAG website.


  4. I live in Sun City Grand west of the 303 section, North of Mountain View Blvd. and South of Highway 60. My concern and question is are there plans to construct Sound Walls on the west side of the 303 and south side of highway 60 when they complete this section of the freeway and the iterchange at 303 and 60?
    Jim Kesslar


Note: Only a member of this blog may post a comment.