Sitting alone in your car through the morning rush is commonplace these days. But not long ago, many of us were packing in together to get to work. In 1970, more than 1 in 5 workers drove to work with others as their main mode of transportation. That didn't hold for long. Today, less than 1 in 10 workers rely on carpooling for their commutes.
What's fascinating here isn't just that carpooling fell, and fell fast; it's that many of society's biggest social and economic trends — the entry of women into the workforce, the growth of singlehood, suburban sprawl — came together to create the perfect conditions for the death of the carpool.
More singles + fewer kids + more car-buying = a car for everyone
"Car availability" — the degree to which a person has access to a car — has grown in recent decades as people get married later, have fewer kids, and buy more cars when they're single and childless. In other words, households started getting more cars, but fewer people. The number of cars per household climbed from 1.55 in 1970 to 2.08 in 2013. Meanwhile, the number of people in each household fell, from 3.14 in 1970 to 2.54 today, according to the Census Bureau.
Having fewer people per household itself makes carpooling less common, as the majority of carpools are "fampools" — carpools consisting of family members. As of 2006, 77 percent of carpools had only two people in them, and the majority of those were family members driving together, according to the Transportation Research Board. Add to that more cars per household, and carpooling is even less likely; a family of three with one car is much likelier to share rides than a couple with two cars, for example.
"Another really silly way to think about this is that the biggest predictor of how much you drive is car ownership," says Richard Watts, research director at the University of Vermont's Transportation Research Center. It's not just that people got more cars because they wanted to be able to drive more; having a car or two around itself makes a person more likely to drive.
In a 1997 study, Erik Ferguson cited this phenomenon of growing car availability as the leading cause of the decline of carpooling from 1970 to 1990, estimating that it accounted for 38 percent of that drop.
Driving became way more affordable
So increased car ownership helped cause the decline in carpooling. But what caused increased car ownership? Affordability is one factor. After 1990, car prices suddenly flattened out, while all other prices continued to climb.
To some extent, gas prices contributed to driving's affordability, as well. Gas prices spiked in the late 1970s and peaked in the early 1980s. The overall falling marginal cost of fuel from 1970 to 1990 is another major reason Ferguson lists for the decline of carpooling during that period.
Fuel economy also improved dramatically over this period, with cars going from an average of 24.3 miles per gallon in 1980 to 34.6 in 2013 — a roughly 50 percent increase, making driving cheaper still and carpooling, accordingly, less necessary.
Cheap and efficient cars and cheap gas meant that more people could afford to drive alone. Not only did the rate of carpooling fall, but the number of carpoolers did too, even as the total number of workers grew over the decades. And many of those workers opted to drive … they just drove alone.
More working women, plus the "Starbucks effect"
The mass entry of women into the workforce in the 1970s may have pulled carpooling rates down for a number of reasons, Watts argues.
"Women started joining the workforce in the 1970s, and that definitely changed these patterns. Now you often have these two-worker households," he says. That meant that households started to have two people who had to get to different destinations to work, making multiple cars more practical. In addition, households suddenly had dual incomes, making them more able to afford additional cars, which meant more cars per household. Even if, say, a husband and wife could potentially drive together, it was more feasible to get an extra car and go separately.
Women are also more likely than men to do "trip-chaining," as travel behavior analyst Nancy McGuckin found in a 2005 study. Women tend to stop for more household errands — shopping, picking up and dropping off kids, etc — than men do, particularly early in the day. Having to do those errands makes packing into a car with three coworkers less practical.
But that same study found that men have picked up this trend of doing errands. Between 1995 and 2001, McGuckin found that men started making multiple stops, but for different reasons. "The growth in men’s trip chaining is robust, but a large amount of that growth is for stops to get a meal or coffee on the way to work, called the Starbucks effect," they wrote.
The fast growth of the suburban population — and the fact that new suburb rings have developed farther and farther away from central cities over the decades — also made carpooling less feasible, and encouraged families to invest in more vehicles.
"People live in these places where there's nothing that they can get to except in a car, and all of that undercuts carpooling," says Watts. "Carpooling works best when it's one trip — home, work, work, home."
Unpredictable work days
There is also some evidence that Americans' work hours are growing more unpredictable. As more Americans work unpredictable schedules or long hours, timing those rides to and from work gets harder and harder.
There are a few trends that you might think would counteract all of the above factors. Millennials, for example, are less enamored with cars than their parents. Technology makes it easier to find people to ride with — Uber has even launched its own carpooling services. And the suburban boom appears to be over, as people shift back to central cities.
But the pull of the above factors may simply be too strong, says Watts. Cheap cars for those who do want them (and bikes and public transit for those who don't want a car) are keeping people from riding together, as is the increase in people working from home. So expect to see more vacant HOV lanes on your morning commute: the carpool is dying, and it's not recovering anytime soon.