What’s Putting the Brakes on the Growth of Driving?

With the exception of a blip during WWII, one iron law governed 20th century transportation: driving always increases. This is true not just because population grew; the relentless surge in driving was strongly evident even on a per person basis. See the data on the last century’s love affair with the automobile here.

But surprisingly, the 2000s appeared to see a halt to that trend, with driving totals stabilizing by decade’s end. Why? I definitely think I would have noticed if there was a colossal world war going on, so are there any other possible explanations for the slowdown?

Last post, I put forward a couple of narratives I find only partially satisfying: high fuel prices, government policy, and a sickly economy.

I do have to amend one argument I made, in which I dismissed greater transit ridership as a possible cause. Eagle-eyed reader Michelle Ernst pointed out to me that I missed the bus – or, rather, missed everything except bus – when I presented data showing that transit ridership was flat throughout the decade. Instead, per capita person miles traveled on transit (including rail) actually rose about seven percent between 2000 and 2008.

My apologies to transit fans; this does speak better of the performance of the industry. But still, it does not contradict my basic point. The reason? Mass transit accounts for a very small share of our total transportation: according to the 2009 National Household Travel Survey, intracity transit (excluding school buses) currently accommodates only about 2.2 percent of our person miles traveled. So it would take very large percent change in transit ridership – much larger than we did indeed see – to take a significant bite out of driving. Moreover, not all new transit trips involve getting people out of their cars; some are trips that might not have happened (or been walking trips) had transit service not improved.

So while transit may take a bit of the credit, we need to look elsewhere. Are there any more promising possible explanations?

First, we may have congested ourselves to the maximum level we can tolerate. With the notable exception of the interstate program, in the face of the dizzying surge of driving in the 20th century we did comparatively little to build more roads. Since 1920, public road mileage has increased by about a third, as driving rose by a factor of about 62. Lane mileage figures, which take road width as well as length into account, weren’t kept until more recently. But they tell a similar story, at least in recent decades.

Lots more driving and few more roads obviously translates into more congestion, the rise of which is well documented by the Texas Transportation Institute among others. It’s quite possible that the congestion problem that so vexes us all (except possibly for us transportation professionals, for whom it provides employment) has caused travel to reach an equilibrium state: at least in larger cities, the value to drivers of marginal, additional trips may be so low that they simply aren’t worth the time cost given the traffic that must be battled.

Another possible explanation is that the share of women in the workplace seems to have stopped growing. While in 1950 only 34 percent of women over 16 worked, in the 2000s that figure appears to have stabilized at about 60 percent. In the past, women arriving in the labor force has meant more commuters. Plus, it meant greater family incomes and thus higher auto ownership levels. This phenomenon seems to be abating.

Speaking of car ownership, it might also hold part of the answer. As pointed out by Adam Millard-Ball and Lee Schipper of Stanford University, auto ownership in the U.S. – indeed, in the developed world – may have reached stable levels. In the past car ownership rose as Americans’ incomes did, but in the U.S., the growth in the number of vehicles per capita has been slowing appreciably since about 1990, and it currently seems to have leveled off at about 700-750 vehicles per 1000 residents. This may be bad news if you live in Detroit, but it is good news if you battle rush hour traffic every day.

Interestingly, in most of the other countries in Millard-Ball and Schipper’s study, car ownership also began to stagnate about the same time ours did, though at lower levels. Now Japan, the U.K., Canada, and Sweden all seem to have relatively stable ownership rates of around 500 cars per 1000 people.

So perhaps the rich world is seeing auto saturation, where just about anybody who needs and can possibly operate a car already has one. In the U.S., we have more than one vehicle per licensed driver, and unfortunately for the auto companies, until we get self-driving cars there’s going to be a cap on the number of autos one person can operate at any one time. So a plateau in the number of vehicles may be contributing to a plateau in the number of vehicle miles traveled.

Another possible explanation for the driving slowdown? Maybe ever more advanced information technology and telecommunications – such as cell phones and the Internet – are enabling us to do things from a distance, eliminating the need for many kinds of trips. But, on the other hand, some believe these technologies might actually cause us to travel more. More on this contentious issue another time.

And a final possible cause for peak driving? It may be that we simply have run out of hours in the day to devote to travel. After all, we need to sleep, eat, work, play, and read Freakonomics at some point. Given that we have to spend at least some time at our destinations, there may be a cap on how much time we can possibly spend getting to them.

Some transportation scholars have theorized that humans have a built-in travel clock; according to this idea, we are programmed to travel about an hour a day regardless of our personal circumstances or the society in which we live. As I have promised, more on this fascinating and controversial theory soon.

PS: My beloved UCLA School of Public Affairs just received a terrifically generous gift from Meyer and Renee Luskin, whose names will from this point forward grace our school and our firstborn children. Indirectly, they are helping to support this column, so feel free to give them credit for anything you like in this space – but continue to address your complaints to yours truly.

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  1. Joshua Northey says:

    Well I am 29, live in Saint Paul, and bike 10 miles to work each day (despite it being -10 all week). My wife takes the bus to her job.

    Could it be that finally some fraction of our generation has learned that there is more to happiness than out-consuming your neighbors? Retiring at 45 is a distinct possibility if you don’t buy cars, giant TVs, cable and 30 other things you no longer need due to the internet. I never understand how so many middle and upper-middle class people manage to spend their way into financial stress. You can support a person in a very high quality lifestyle in most American cities for 15,000-20,000/year.

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  2. Sbard says:

    I remember reading some commenters discussing this issue on an automotive blog somewhat recently. The general consensus is that for a lot of baby boomers, having a car and driving was either a form of recreation or a necessity for such, e.g. driving to the movie theater, going on road trips, etc. For a lot of younger people nowadays, driving is seen more as an expensive hassle. They don’t need to go cruising around town to have a social life. They can keep in touch with their friends online and instead of going out for a movie, they stay in and watch them on the big flat screen TV. In addition, the dramatically lower cost of flying compared to 30-40 years ago makes them less likely to take a three day road trip when they can just fly there on Southwest for a couple hundred dollars. The proliferation of internet shopping has also helped. I know people who will order things like shampoo on Amazon with Amazon Prime’s free 2-day shipping because they don’t want to deal with the hassle of driving to the grocery store or pharmacy to pick it up.

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  3. D. P. Lubic says:

    I’m of the opinion it’s a variety of things working in combination, as has been suggested above. I would also add that a component that hasn’t been mentioned is that driving is so common now that it’s no longer as special as it once seemed to be (“What’s the big deal, my grandma drives. . .”), along with it not being fun due to congestion, costs, and those driving restrictions on younger drivers today.

    There are also the shadows of classmates who have died in wrecks; there were three such stories in my local paper in as many weeks recently. That has to have a chilling effect. Reportedly some teens have taken to calling cars “deathmobiles.”

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  4. Brent says:

    It occurred to me about fifteen years ago that I could save $125 (now over $200) per month in parking costs if I walked to work. It also occurred to me that walking would provide a bit of exercise, fresh air, and would mean no more time lost in traffic tie-ups. So I moved.

    I never thought I was particularly trendy, but I find myself in the middle of a trend. And here all along I just thought I was being frugal.

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