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Sat Jul 18 12:09:24 PDT 2015

Tools and Services: Traffic Volume Linkage Tool

CEHTP now offers custom data linkage and analysis services for traffic data. 


We have retired our previous traffic linkage tool and will launch a new tool in early 2017, with more extensive traffic data and additional features. 


Please submit a data request using the instructions outline under How do I submit a data request?  For more information, see FAQs below or contact us at tracking@cehtp.org.  

CEHTP's traffic volume linkage tool allows the user to obtain information about how much traffic passes near a specific location. The CEHTP service assists users who are interested in calculating traffic information for many locations.

We have retired our previous traffic linkage tool and the new tool's projected launch is late 2016

A user can use the tool to learn how many vehicles travel near a location every day on average. This tool is especially useful for researchers who are interested in looking at traffic volume related to health events for which address-level data are available.

Our services have been used recently to provide traffic volume data by zip code for Cal/EPA's CalEnviroScreen. 

Users who are interested in air quality data and information can also visit our air quality data query.

The service in the previous version of the tool calculated traffic metrics using the CalTrans Highway Performance Monitoring System (HPMS) data in California for 2004.

The new traffic linkage tool will be available in 2017.  In the meantime, you can use CEHTP’s custom data services to request data.  The new tool will use an updated traffic dataset that is more extensive and accurate (see What traffic data services are you providing in the meantime?).  It will also provide the same metrics for any given point as the previous tool, including:

Unadjusted metrics

  • su: Sum of all unadjusted traffic volumes within buffer (vehicles/day*)
  • hu: Unadjusted traffic volume of highest segment within buffer (vehicles/day*)
  • nu: Unadjusted traffic volume of nearest segment within buffer (vehicles/day*)*average annual daily traffic (AADT)

Gauss-adjusted metrics

  • sg: Sum of all Gauss-adjusted traffic volumes within buffer (vehicles/day*)
  • hg: Highest Gauss-adjusted traffic volume segment within buffer (vehicles/day*)
  • ng: Gauss-adjusted traffic volume of nearest segment within buffer (vehicles/day*)

Length-adjusted metrics

  • sl: Sum of all length-adjusted traffic volumes within buffer (vehicle-km/hr)
  • hl: Length-adjusted traffic volume of highest segment within buffer (vehicle-km/hr)
  • nl: Length-adjusted traffic volume of nearest segment within buffer (vehicle-km/hr)

Gauss and length-adjusted metrics

  • sgl: Sum of all Gauss- and length-adjusted traffic volumes within buffer (vehicle-km/hr)
  • hgl: Gauss- and length-adjusted traffic volume of highest segment within buffer (vehicle-km/hr)
  • ngl: Gauss- and length-adjusted traffic volume of nearest segment within buffer (vehicle-km/hr)

Distance and direction

    • hdist: Distance to highest segment within buffer (meters)
    • hdir: Direction to highest segment within buffer (degrees ccw** from east)·         
    • ndist: Distance to nearest segment within buffer (meters)
    • ndir: Direction to nearest segment within buffer (degrees ccw** from east)

    *annual average daily traffic

    **ccw = counterclockwise

    CEHTP provides custom data linkages and analysis services for a fee, based on the extent of the request.  Fees waivers may be granted to community-based organizations and others on a case-by-case basis.


    We can calculate traffic metrics (see When will the new tool be available?) for one or more points or polygons (for example, the sum of length-adjusted traffic segments within a certain radius of a point).  The results can be returned to you in spreadsheet and/or map format.  Currently, we can make the calculation based on your choice of one of two datasets:

    1.       Our original 2004 dataset. This dataset was based on Caltrans data from 2004 and was the dataset previously used in the prior version of the traffic tool. A calculation based on this data should be directly comparable to previous calculations you may have made using our tool.

    2.       Our new dataset. This dataset was developed for the new version of the traffic tool and was derived using TrafficMetrix spanning a date range from about 1970 all the way to 2012. TrafficMetrix is created by Kalibrate, a private vendor. This dataset is considered more accurate and extensive than existing Caltrans datasets. However, direct comparisons to metrics created using the old traffic tool will not be possible, although results should be similar. There may be further changes made to this dataset before it becomes publicly usable on our site via the new traffic tool. At that time full documentation will also be provided.

    It should also be noted here that in general, traffic sampling is typically flawed due to nonsystematic sampling (both in time and in space), differing measurement methods, lack of measurement on certain types of roads, and other problems. Therefore, one approach is to assume that no measure of average annual daily traffic is completely accurate and all are best estimates – and therefore that differences between a Caltrans-based calculation and TrafficMetrix-based calculation are not surprising and should be, in fact, expected.

    Please read the FAQs before submitting a request to make sure you understand all of the potential options and restrictions. If you would like to proceed with a custom data request, please email tracking@cehtp.org with "Custom traffic data request" in the subject line. In your email, please include answers to the following questions:

    1.       What location or set of locations you would like to create metrics for?

    2.       Which metrics will you need in your results? (refer to When will the new tool be available? for a list of available metrics. Please be specific)

    3.       Which dataset you would like your metrics to be based upon? (see What traffic data services are you providing in the meantime?)

    4.       How did you find out about the California Environmental Health Tracking Program as well as our traffic tool?

    5.       What do you plan to use the data for?

    6.       How do you anticipate your work impacting public health?

    7.       What is the duration of your project/how often do you predict needing to access traffic data?

    8.       Do you have any comments on the tool or the data?


    We will respond to your request as soon as possible.

    Depending on volume of requests, results will be returned within 2 weeks. If your request is urgent, please let us know and we may be able to expedite your request.

    Anyone can access current geospatially associated traffic data published by Caltrans on their website, for free at: http://www.dot.ca.gov/hq/tsip/gis/datalibrary/Metadata/AADT.html. These data are provided at point locations instead of for line segments, so some calculations based on this dataset may require more processing. To use data at the link above, you will need to have a GIS program installed on your computer and the ability to manipulate shapfiles. Traffic Counts for individual roadways are also available from CalTrans here: http://traffic-counts.dot.ca.gov/Using these sources may require additional GIS processing, but may be sufficient for basic data needs.