How to Estimate Vehicle Miles Traveled (VMT)

VMT is a measurement tool used by transportation agencies that sums the miles traveled for all vehicles in an area over a certain time period. VMT indicates travel demand and behavior in an area, and thus is integral for transportation planning and policy decisions. This guide will show you one way to estimate VMT (Vehicle Miles Traveled) for a project study area using StreetLight’s Calibration feature and Zone Activity Analysis Project Type.

To calculate VMT, we multiply the calibrated result by the average trip length provided via the Zone Activity Analysis Project. This calculation provides you with an estimated total VMT for all trips that started, regardless of their destination, and ended in our area of study, regardless of their origin.

For this guide, we will use Pasadena, CA, as an example. California relies heavily on VMT when developing and implementing urban transportation policies. Pasadena is working to increase access to public transportation in their area to decrease their VMT. We can use StreetLight InSight to capture a current estimate of VMT within the city before adding public transportation, and then that number can be compared to VMT estimates after adding public transportation to gauge if VMT actually decreased.

Step 1: Create the Zones and Zone Sets

To get an estimated VMT you will need to create two Zone Sets. Learn more about how to create Zone Sets.

Calibration Zone Set

The first Zone Set is a Calibrated Zone Set. This will be used to get Estimated Trip Counts and does not need to include roads in your study area. Learn more about how to set up our Calibration in StreetLight.

For a Calibration Zone Set, you can use your own counts or StreetLight’s AADT data to calibrate your Zone Set.

For our example, we will call our Calibration Zone Set “Calibration Zone Set (VMT Pasadena),” which uses various roads within Pasadena and our StreetLight Data AADT data to calibrate our Zone Activity Analysis.

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Zone Activity Zone Set

Create a second Zone Set that is over the area where you want to collect VMT data.

  • It must cover the entire area of analysis
  • Polygon or Line: Polygon
  • Pass-through: No

We will name our second Zone Set, “Pasadena (VMT)”.

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Pro-Tip: Make sure to click “Show OSM Layer" drop-down menu and pick the OSM layer you want to view. You will be able to select "Vehicle," "Bicycle," or "Pedestrian." The OpenStreetMap road layer is what we use to lock our trips to the underlying road network. The Calibration Zone must cover this layer to pick up trips traveling along the road.

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Step 2: Create a Project

To get VMT, you will use the Zone Activity Analysis Project Type. Learn more on creating a Zone Activity Analysis.

For “Travel Type,” use “Personal,” and for “Data Source Type” use “Navigation GPS data”. One could use LBS data, but generally, we recommend using GPS data for this analysis because it collects vehicle trips exclusively, whereas LBS data could include other modes such as bicycles, trucks, buses, etc. Learn more about choosing a data source.

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Use your project area Zone Set, as the “Selected Zone Set(s).” Use your Calibration Zone Set in the “Selected AADT Calibration Zone Set(s)”

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Note:

  • Under “Project Options,” ensure that the “Day Parts” is set to “All Day.”
  • Under "Project Options," ensure that you picked a Calibration data period by clicking "edit" under "Calibration Data Period." You can pick either 2017 or 2018 for your data period. Learn more about calibrating with StreetLight AADT. 

Our Example

We chose to calibrate with AADT from 2018 because we analyzed months from 2018. We recommend calibrating with the data period that is closest to your time period of analysis. This means if you are analyzing 2016, you should calibrate with AADT from 2017. 

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Step 3: Interactive Visualizations

You can visualize your Project in our Interactive Visualizations. While the visualizations are useful, it can be easier to get information by working with the downloaded Metrics. This will help you get a better understanding of the full VMT analysis. Learn more about our Interactive Visualizations, in general. Learn more about interactive visualizations for a Zone Activity Analysis, specifically.

Step 4: Further Analysis of the Metrics

4a. Download your Metrics. Learn more on downloading Metrics.

4b. For VMT estimation, select at least these items:

Note: If you choose to download the default options (or your Project is small) the .zip file will be delivered immediately. If you choose to download anything other than the defaults for a large Project, you may be warned that the download needs to be generated and a link to download the Project Metrics will be emailed to you.

4c. After opening the file “zone_traffic_all,” you will see the information pictured below. The download already includes the average trip length results for trips that start in the Zone, and those that end in the Zone.

4d. In column P, calculate the average daily VMT for the trip starts and ends by multiplying the “Avg All Trip Length (mi)” by “Zone Traffic (Calibrated Index)”.

If you have more Day Parts or Day Types that you want to analyze, the spreadsheet will contain more rows of information. For ease of analysis, insert a pivot table with filters for Day Type, Day Part, and Zone is Pass-through.

By filtering out the Pass-through Zone data, you are left with the total trip volume for the project study area, which is multiplied by the average trip length to obtain the current snapshot of average daily total VMT for the project study area.

Note:

  • A Zone Activity Analysis that uses non-Pass-through Zones includes trips that start or end in the Zone. This includes all trips that start and end in the Zone, regardless of either origin or destination. Keep this in mind while assessing your calculated VMT.
  • If you would like to only include trips that start or end in your Zone of interest please reach out to the Support Team at support@streetlightdata.com
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