By: Laura Schewel on September 11th, 2015

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4 Negative Impacts of External-External Trips


StreetLight Data is publishing a series of blogs and eBooks about national transportation trends, based on running StreetLight InSight® Metrics across the country. Currently, we’re investigating the differences in internal and external vehicular trip-making for counties in the Continental US. Check out the full eBook for more details.

The share of "external - external" trips, defined as those that pass through an area without stopping, are important to understand for a numbers of constituencies. The map below shows the share of personal trips that "just pass through" a county. Intuitively, counties in the center of the country have higher pass-through rates. In addition, the influence of major highways, such as I-95 in the East and I-90 in the North can be seen.

external trips

Why are these "pass-through" trips so important to measure? The reason is that there can be significant negative impacts for the community in which these trips pass through. Below, we detail the key concerns.

Wear and Tear

First, these trips create wear-and-tear on local roads, as well as traffic jams, without adding much to the local economy and tax base by stopping and shopping, dining, participating in community life, etc.

Congestion (Air and Noise Pollution)

Second, these trips can contribute to local air and noise pollution to residents, as well potentially add to congestion during peak hours.

Greenhouse Gas Implications

Third, depending on regional allocation procedure, these trips may contribute to a locality’s vehicle-miles traveled or greenhouse gas emissions tally, which can have implications on regulatory compliance, taxes, and more.

Economic Development (Missed Opportunities)

Fourth, these trips may be missed opportunities! These vehicles, and their occupants, are already just a few feet away from local attractions and business. These drivers can be convinced that the same type of destinations they want exist closer to them by marketing or investment in certain types of jobs/shopping/etc.

External-external trips measures are one of the most in-demand measures by transportation departments across the country. In a recent report done by StreetLight, we were able to show the top three counties for pass through trips (measured as a share of all trips). To read more on this study, and internal vs. external travel, click here.


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