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Noise Impacts & Analysis


Northwest Rail Line is a proposed 41-mile commuter rail project, which will run along the current BNSF Railway line from Denver Union Station to Longmont, passing through North Denver, Adams County, Westminster, Broomfield, Louisville and Boulder. The Northwest Rail Line Environmental Evaluation will identify how this project may impact the community and the environment. The study will recommend ways to minimize these impacts in accordance with the National Environmental Policy Act (NEPA). Noise is one impact the study will examine. 

What creates commuter rail noise?
Train horns, wheel-rail interaction, diesel engines and vehicle cooling fans all contribute to train noise. Train horn noise is the loudest noise and is the same, regardless of the type of train (diesel or electric). The Northwest Rail Line will operate with Diesel Multiple Unit (DMU) commuter rail vehicles.

Why are train horns necessary?
Federal Railroad Administration (FRA) safety standards require trains to sound their horns as they approach every railroad crossing. FRA requires freight trains to sound their horns at 110 decibels. Other requirements include the following:
  • The horn noise level must be in the 96-110 decibel range at 100 feet in front of the train and 15 feet above the rail;
  • Horns must be sounded 15-20 seconds before the train reaches a crossing, but not beyond a quarter of a mile away; and
  • The horn sequence must consist of two "long," one "short," and one "long" sound before the train reaches the crossing.
How will RTD analyze noise impacts?
The Northwest Rail Line study took existing noise measurements throughout the corridor and at proposed station areas. The study identified the noise levels that would be added by the project. The difference between the existing and added noise levels determined whether the project's impacts are mild, moderate or severe. In places where impacts are identified, the study recommended ways to minimize such as track improvements, noise walls or Quiet Zone crossings.

How will the study determine whether noise is mild, moderate or severe?
For transit projects, moderate and severe noise impacts were determined by Federal Transit Administration (FTA) criteria. The degree of impact is based on comparing the predicted noise from the project with the existing (baseline ambient) noise levels at sensitive locations.

Where is noise measured?  
To determine existing noise, measurements are typically made at different locations within a few hundred feet of the track; some of these locations are within ΒΌ-mile of railroad crossings (where train horns are sounded) and some are not.  For Northwest Rail, where noise from existing freight trains is loudest near the track, the measurements are used along with the noise from existing freight train operations to generalize the existing noise conditions at all locations along the project.  Noise impact is then assessed by forecasting the noise the project will create and comparing it to the existing noise. Although typically limited to areas within a few hundred feet of the tracks, noise impacts may extend farther out depending on various conditions. 

Are the noise measurements repeated over the course of a certain time period or are they a one-time measurement?
In residential areas, noise is typically measured and assessed over a full 24-hour period at representative locations.  At locations with primarily daytime use (e.g. schools, churches, and parks), noise is typically measured and assessed over a one-hour period during the day. 
 
Do the noise measurements take land contours into account?
Yes. The noise analysis accounts for the elevations of the source (trains) and receiver (homes) as well as the ground in between.  These factors affect sound transmission, resulting in greater noise levels where the sound travels in an unobstructed path high above the ground and in lower noise levels where the sound path is shielded by intervening buildings or topography. 
 
When will I know what the noise impacts from the Northwest Rail  Line will be?
The results of the noise impact analysis will be available in the summer of 2008 and shared at project-wide public workshops. If you are on the project mailing list, you will be notified of the workshops. If you are not currently on the mailing list, you can sign up by clicking here.

Additional Resources
RTD FasTracks Noise Fact Sheet (Coming Soon)
The Federal Railroad Administration - Train Horns at Grade Crossings
Federal Transit Administration Noise and Vibration Manual

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