America's Driving Habits as of September 2021
The Department of Transportation's Federal Highway Commission has released the latest report on Traffic Volume Trends, data through September.
"Travel on all roads and streets changed by +7.9% (+19.5 billion vehicle miles) for September 2021 compared with September 2020. Travel for the month is estimated to be 266.7 billion vehicle miles." The 12-month moving average was up 0.64% month-over-month and up 5.6% year-over-year. If we factor in population growth, the 12-month MA of the civilian population-adjusted data (age 16-and-over) was up 0.58% month-over-month and up 5.2% year-over-year.
Here's a detailed map of regional driving in September:
Here is a chart that illustrates this data series from its inception in 1971. It illustrates the "Moving 12-Month Total on ALL Roads," as the DOT terms it. As we can readily see, the Great Recession had a substantial impact on our driving habits, but habits bounced back over the next five or so years. The decline in driving was most likely related to the cost of gasoline during that time period (see fourth chart below). The COVID-19 pandemic has had a massive impact on driving as Americans are staying home for work, meals, and entertainment.
The rolling 12-month miles traveled contracted from its all-time high for 39 months during the stagflation of the late 1970s to early 1980s, a double-dip recession era. We are currently in the most rapid decline we've ever seen, though miles traveled are still not at all-time lows, even when adjusted for population (see below).
The Population-Adjusted Reality
Total Miles Traveled, however, is one of those metrics that should be adjusted for population growth to provide the most meaningful analysis, especially if we want to understand the historical context. We can do a quick adjustment of the data using an appropriate population group as the deflator. Let's use the Bureau of Labor Statistics' Civilian Noninstitutional Population Age 16 and Over (FRED series CNP16OV). The next chart incorporates that adjustment with the growth shown on the vertical axis as the percent change from 1971.
Clearly, when we adjust for population growth, the Miles-Traveled metric takes on a weaker look. The nominal 39-month dip that began in May 1979 grows to 61 months, slightly more than five years. The trough was a 6% decline from the previous peak. The COVID-19 recession has put us at levels last seen in the late 1980s.
About that Population Adjustment…
Why use the CNP16OV data for the population adjustment? Wouldn't it make more sense to limit the population to licensed drivers? The correlation between license holders and actual drivers is far from reliable. Many license holders in households do not drive, especially in their older years. According to Census Bureau data on gasoline sales, dollars spent on gasoline peaks for people in their late 40s and falls off rather quickly after that.
In fact, there's a good case for using the Census Bureau's mid-month estimates of total population (POPTHM) rather than civilians age 16 and over for the population adjustment. The reason is that a portion of total miles traveled is specifically to support children's needs (daycare, schools, children's activities, etc.) and the needs of elders who might have licenses but no longer drive. Ultimately the division of miles traveled by either population group (CNP16OV or POPTHM), while not a perfect match with drivers, is a consistent and relevant metric for evaluating economic growth.