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New data show a clear mobility "continuum" from car-only to car-less.

As we saw firsthand during our nine-month Future of Transportation series, U.S. cities are working toward more balanced mobility systems that offer a range of reliable trip options. But just how many Americans take advantage of these options on a regular basis? It's a tough question to answer with much precision, but it just got a lot easier with a new study from Virginia Tech scholars Ralph Buehler and Andrea Hamre—one of the first of its kind based on a representative national population.

The short answer: most of them. The longer short answer: some of them, but far from all. We'll start with the conclusion (via Transportation) then work back through the details:

Only 28 percent of Americans solely rely on a car during a week. The majority of Americans are multimodal car users who drive and make at least one weekly trip by foot, bicycle, or public transportation. Stricter definitions for multimodal driving additionally show that about one in four American car users make at least 7 trips by walking, cycling, or public transportation during the week.

Buehler (who contributed to our Future series) and Hamre based their findings on an analysis of data from the 2001 and 2009 National Household Travel Surveys, which combine single-day trip diaries and broader travel questionnaires to track mobility trends of hundreds of thousands of U.S. residents. Let's start at the daily level (which we chart below). More than three-quarters of NHTS respondents relied on a car alone for their single-day travel needs, though this share of "mono-modal" driving fell slightly over time, while the (very modest) share of car-less daily travelers rose.


So on any given day, a lot of Americans only drive—something we already know quite well from commute trends. But the weekly habits reveal a more complex picture of mobility behavior. Here we see that the share of Americans who rely only on a car for the entire week is in the clear minority, under 30 percent in both years, with those shares also declining over time. Car-less travelers rise again over time. And multi-modal drivers, who use a car plus at least one other mode during the week, make up nearly 65 percent of all respondents in both years. Again, we chart the findings from Buehler and Hamre:


What this means is that a lot of people who only drove a car on the day they filled out their trip diary also indicated in other questions that they used an alternative mode at some point during the week—roughly 63 percent of one-day drivers in 2001 and 64 percent in 2009, to be more specific (not shown above). The reverse behavior also holds true, though to a much lesser degree. Of the survey respondents who didn't use a car at all during their diary day, about 10 percent in 2001 and 11 percent in 2009 did drive at some point during the week.

The thing is, not all multi-modal travelers are created equal. Some people use whatever mode is the best option for a particular trip. Others may be more accidentally multi-modal—maybe they'd prefer to use the car but a spouse is stuck in traffic when they have to leave the house. The difference is best captured by how many non-car trips a person makes a week; it's fair to say that the more often someone takes an alternative mode, the more multi-modal that person is.

So Buehler and Hamre established four thresholds to distinguish different levels of multi-modality: one, three, five, and seven non-car rides a week, in addition to some driving. Let's take the 64.9 percent of respondents who met the minimal multi-modal threshold of one non-car trip in 2009. As expected, the numbers decrease as the thresholds rise, but they remain impressive. About 48 percent of respondents took at least three non-car trips in a week, and about 33 percent took at least five. When the multi-modal threshold reaches seven non-car trips a week—an average of one a day—nearly a quarter of all respondents still met the mark.

The 2001 figures are similar. We chart both years below:


So that's technically a multi-modal majority for America, but it's also nowhere near a simple one, and by the strictest measures it's only a rising minority. Buehler and Hamre see this as a "continuum of mobility types," with car-only living on one end and car-free on the other, and most Americans stuck somewhere in the middle. What's also pretty clear, if far from overwhelming, is which direction the movement along this spectrum is heading.

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