What's driving your county's vehicles miles traveled? In a recent report, StreetLight used its proprietary Route Science® technology to create the trips and run the analyses. First, we received data from a variety of GPS Mobile devices from our partner INRIX. These devices include a mix of smart phones with locational services, cars with navigation systems, trucks with commercial fleet management devices, and more. We used data from four months in 2014 and 2015, one in each season (February 2015, April, June, September 2014).
We analyzed nearly 500 million trips to create this report. A trip is defined as ending when a vehicle turns off, or when a device is stationary for more than a few minutes. For each county, we looked at each trip that touched the county. Then we characterized its starting point and ending point as inside or outside the county. This allowed us to compare how many trips were internal, external, or in/outbound to each county. We also calculated the trip length (the actual trip, not the Euclidean distance) to create the average Vehicles Miles Traveled values.
For the VMT share calculations, we only included the VMT that was inside the borders of the county. In other words, we “clipped” the trip at the border. Therefore, for the inbound, outbound and “just passing through” trips, we did not count the portions of the trip in other counties.