Simple GIS Tools for Traffic and Transit Noise Studies

ABSTRACT

Many companies are marketing complex programs for integrating ArcView and noise modeling software. While these programs are impressive, they require the user to have expansive knowledge in both the noise and computer software fields. This paper will demonstrate simple, out of the box ArcView tools that can improve noise modeling for both traffic and transit studies. Techniques for improving visual presentation for the results will also be shown.

INTRODUCTION

Noise studies for transportation projects in the United States are conducted in accordance with the following:

· Federal Transit Administration (FTA) FTA noise impact assessment guidelines for transit and rail projects

· Federal Aviation Administration (FAA) Integrated Noise Model (INM) for aircraft noise

· Federal Highway Administration (FHWA) Stamina Highway Traffic Noise model or other state models that utilize the same algorithms as Stamina

These models and the new FHWA Traffic Noise Model (TNM) work well once the data is inputted and if all you need as output are noise levels at each of the corresponding receivers. Using readily available tools in ArcView, a noise modeler can simplify and improve on data input, analyze noise impacts from more than a few receivers, and present the impacts and noise abatement measures in map form that the public can easily comprehend.

Model Input

Traffic noise models and ArcView both use X, Y coordinates to place the data, but how do you get the coordinates from ArcView into the noise model? Some of the older models require scaling maps or use digitizing software developed by the user. The newer models such as, TNM will import this information from a digitizer table. Both of these methods have similar drawbacks. The data need to be printed out, and the modeler has to make sure the coordinates are consistent from sheet to sheet. Using ArcView as a “heads-up” digitizer not only improves on the coordinate input, but also requires no printing. In addition, ArcView has the ability to view different CADD and image formats in their native format, which allows the user to digitize from the same files that other parts of the project are using.

The following steps should be use to digitize the noise model. First, start by digitizing the existing roadway. Start with the view up and the background themes turned on. Next, create a new point theme, naming it, x-roads or ex-roads. With the file in edit mode, open the theme attribute table and add a field for X, Y, and Z. These fields need to have the space to hold the coordinates with a least one decimal place. For the roadway files, add a field for the roadway name, and one to identify the point location, e.g. station number. This will save confusion while importing the coordinates in to the noise model.

Start inputting the points to create your roadway. Beginning at one end of the project and going with the flow of traffic, input points digitizing a line of points in the middle of your traffic lanes. With the attribute table open, the roadway name, station number, and Z value, can be added, as the points are inputted. Once all the points for your roadway entered in, highlight the field for the X value and calculate the x-coordinate using the Avenue function “shape.getx”, then highlight field of the Y field and calculate the y-coordinate using the function “shape.gety”. The shapefile’s dbf file now contains all the spatial information needed to input the roadway geometry into any noise model.

To input the coordinates into Caltrans Sound 2000 or FHWA TNM, you can open the dbf file in Excel and copy and paste between the programs. The coordinates for barriers and receivers can be obtained in the same manner. For the barrier attribute table, add the following fields: barrier name, x, y, ground level z, z of top of wall, and Station ID. For the receiver attribute table use the following fields: receiver name, x, y, z and z plus 5 feet. Calculate the z of top of wall and z plus 5 feet once you have input your points.

Once the existing roadways are entered, the proposed roadways can be created. To do this, create a new shape file out of the existing road file. The new file will contain all the attributes of the existing road file, but will allows for new roadways to be input or the existing roadway points to be move and change the coordinates recalculated. One advantage to this is, when widening a roadway, by copying the existing roadway file, the points can be move to the new center of traffic lanes and recalculate the x and y coordinates then copy and pasted them into the noise model. Adding new barriers and receivers is just as easy. The greatest advantage to using ArcView is the time and space saved if changes are needed in the model. Since the data is stored digitally, there is no need to keep paper plan sets of your input. Using ArcView, it is possible to pull up, the themes, input the new data, calculate the new and then copy and paste into the noise model. There is no need to mess with re-registering the plan sheet on the digitizer table, or measuring new coordinates by hand.

Modeling Viewing

ArcView’s event theme function can be used to view and update older noise models. FHWA TNM and Caltrans Sound2000/S32 both have the ability to view the input data, while FHWA Stamina noise model does not. All of these viewers are good for showing the noise model data in relation to itself, but they lack the ability to show how the data relates other elements of the project.

To view the model data in ArcView, first convert it into a DBase file format. FHWA TNM will allow the input tables to be exported to comma delimited files that can be open in Excel and saved in a Dbase file format. Stamina and Sound2000/S32 require the input to be in a text file format. This format can be opened in Excel as a space delimited file, which will then need to split the roadways, barriers, and receivers and save them into different files. The DBase file should contain at least the fields to hold the x and y coordinates, while other useful fields are z coordinate, point name, and roadway name. Once the DBase files are created they can add them to the ArcView project. Add an event theme using the “add event theme” option under the View pull down menu. In the dialogue box select the table and the fields that correspond to the X and Y coordinates. Once the okay button is hit, assuming the GIS data have the same coordinates, the points should be shown overlaid on top of the existing GIS data. Not only does show how accuracy the noise model inputs, but shape file can be created out of the event theme.

Analyzing and Display the Results

Now that the data is entered and the model has been run, the projected noise levels and proposed mitigation need to be analyzed and show overlaying with other project data. One-way ArcView can help with this analyze is by creating noise level contours. First, the distance to the noise contours would need to be determined in the noise model.

Once this data is obtained, there are two ways that ArcView can create the contours; both use the buffer command. If a single buffer at the same distance around your project needs to be created, you can enter a distance measurement under the “at a specified distance” in the buffer dialog box. If several buffers for different noise level or a buffer that varies along the project needs to be created, additional distance fields to the attribute table will have to be added. For example, to create buffers for the 60, 65, and 70 dBA noise contours, start be creating fields called 60 dBA, 65 dBA, and 70 dBA. In these fields, put the distances that were calculated by the noise model for each of these noise levels. In the buffer dialog box choose “at a distance from an attribute field.” Because the buffer tool can only create one buffer from an attribute at a time, each noise contour will need to be created into separate shape files. The geoproccessing tool “union” can then be used to combine the contour buffer into one file. An attribute can then be added to identify the noise level that each polygon represents. To create buffers of varying distances, split the line that will be buffer and assign each segment a different buffer distance. Since the buffers are a polygon theme, the geoprocessing tool can be used to clip or intersect other themes with the buffers. The clip tool is useful to obtain the number of sensitive elements within in one contour level. Once the data is clipped the new theme will contain only the elements within that contour level. The data can now be printed and plotted on an ArcView layout. To create a theme that contains multiple noise contours, use the intersect tool. This tool will create a new theme which contains the attributes from both intersected themes so that the data can be grouped by both noise level and element type. This can also be shown in an ArcView layout. This approach is useful for keeping an inventory of noise migration measurer for individual buildings or sensitive elements. Adding a unique value to each element and linking that to the same value in the database file can create quick plots showing the current work status of each element created to show how and where the work is progressing.

Example One:

ArcView was used to digitize the roadways, barriers, and receptors for a segment of Interstate 10 in Los Angeles, California. This approach saved time in several ways. First, the coordinates for the existing conditions were taken directly from ArcView and placed in the model (Figure 1). This saved the time it takes to print 10 to 11 plan sheets and register these sheets on a digitizer table (Figure 2). Second, once the existing points were inputted in to ArcView, time could be saved on the build conditions by simply copying the ArcView theme to a new theme, moving the needed points, recalculating the x and y coordinates (Figure 3). When new receptor sites were added, the coordinates were taken directly from ArcView without having to re-register the plan sheet on the digitizer. Finally, with the data already entered in, ArcView detailed graphics that show the proposed barrier locations can be created by tracing a line over the points from the wall theme (Figures 4 and 5).

Figure 1 – View of I-10. Roadway Points input into ArcView.

Figure 2 – View of I-10. This view contains 10 map sheets.

Figure 3 – A view showing existing and proposed build points.

Figure 4 – Barrier and Receiver Points input in to ArcView.

Figure 5 – Barrier input for Final Graphics.

Example 2

State Route 56, San Diego. After the project was built, the city asked that a portion of area be remodeled using survey data obtained in the field. The original noise modeling was completed two years earlier and there were no common attributes between the survey data and the coordinates in the noise model (Figure 6). The survey data was converted to feet and the noise model barrier data was converted into a DBF file. The add event theme was used for each theme. The themes could then be viewed side by side in ArcView. (Figure 7)

Figure 6 – Noise Model Data and Survey Data

Figure 7 – The matching of Noise Model Data and Survey Data.

Example 3

The following are samples of simple buffers and their uses.

Figure 6 – I-40

This figure shows noise contours created using the buffer tool. The 66 and 71 dBA contours were created using a distance obtained from the attribute table. The noise contours were at different distances for different areas of each alignment. The area to the left of center best shows how the contours differ.

Figure 7 – Austin LRT

A buffer analysis was used to identify areas of potential impacts by the proposed transit line.

Example 4

Noise contours created in FTA INM were brought into ArcView and made into polygons (Figure 8). Using the geoprocessing tool, the TAZ zone theme was intersected with the contours (Figure 9). The new theme was then used to calculate the potential future population within each noise contour (Figure 10).

Figure 8 – Noise Contours overlaid on Air Photo.

Figure 9 – Noise contours overlaid with traffic analyze zones (TAZ).

Figure 10 – Traffic analyze zone clipped to noise contours and the new population calculated.

Example 5 – SR15/40th Street, San Diego.

Using ArcView ability to linking tables can enhance project study and status.

Figure 11 – Tables linked by site numbers, show noise levels at each site.

Figure 12 – Attribute table linked with database used to chart study progress.

Conclusion

By using the basic ArcView tools and simple techniques outlined above the noise modeler can improve on the accuracy of the coordinate input, and decrease the amount of time spend on both the initial data input and any revisions to that data. Once the data is in ArcView these techniques can be used both analyze noise impacts and quickly plot the results in a way that are easy to comprehend.

Kevin Keller, AICP

GIS and Noise Specialist

Parson Brinckerhoff Quade and Douglas