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.


Tzipporah

"While in 1950 only 34 percent of women over 16 worked," I know you're generally blind to anything but the formal economy, but seriously? This is 2011.

Domestic labor is still work, and now more than in the 1950s requires a car. How many SAHMs do you know who don't spend a lot of time on the road?

dc

I don't know if the measurement of driving included business related driving or not. Perhaps you could compare the amount (volume and money value) of goods bought at stores pre-internet to the amount now bought on the internet and delivered.

It also occurs to me that I haven't driven to a bank in years. I go to the movies less and watch it at home. I go to the library less. And "they" have built everything into various strip malls so I never drive as far as i did when I was much younger.

Now that I've thought about it, why is it surprising that we're driving less?

Chan Lee Meng

I'm wondering about the impact of car-sharing services like Zipcar and CityCarClub (UK).

Most member end up selling their primary car, and change their habits to only make occasional use of a shared car - mainly for out-of-town trips, moving large items, or other special occasions.

This means there are hundreds of thousands of people who still drive, but they drive a lot less often than they used to, and they do not own the cars.

John

When I was younger I use to put 30k miles a year on motorcycles, but now it's less than 15k on a car or truck. The economy being what it is and fuel prices being kind of high we don't travel around the area like we use to. Now that my kids are driving I've tried to get them to figure out the cost of road trips they realize that it's often cheaper to fly some places.

PaulRino

Population Growth.
Thirty Years ago it was a pleasure to drive a car along the backroads. Today, there are no backroads.

In the suburbs, if there's 100 yards of free road ahead of me, there's some idiot in a side street that will jump out in front of me and do the speedlimit - 5 mph for about 2 miles.

Your grandfather, who used to do 20+ over the speed limit, is now crawling along at EXACTLY the speed limit or again, 5 less. Because he's not capable of driving the speed limit safely. So, yes demographic switch as well.

And finally, do you know what insurance costs? Do you know what WalMart pays? With Wall Street stupidly building the Chinese economy, we have a huge population that can't afford a car.

Where've you been? Out of the country for 20 years?

Peter

Both sets of my grandparents died in the 1990 to 2000 range. Both of my grandmothers never drove. All of their grandkids drive.
I think we have reached the point where the older people who did not drive have been replaced by drivers. Now when people die, they are drivers and are being replaced by drivers.

Based on older relatives, and older relatives of friends, and so on, 1925 seems to be a dividing line for women and driving. Women born prior to 1925 generally never learned to drive, though some picked it up later in life when their husbands died, while almost all women born after that date have driven all their adult lives.

Dev

It would be interesting to see if the drop is significantly higher in cities with ERP pricing (like here in Singapore). This could definitely by one reason for the abatement in peak hour driving.

Jeff

Like #17, I live in a dense area with services walking distance from my home. Upon graduation, (15 yrs ago) I commuted 25 miles and spent an hour in the car each way. Given this congestion and time waste, now I seek jobs close to home, or work from home and minimize my driving. I figure it costs $5+ every time I turn the car key with fuel and parking costs, $2.50 to ride a train or a bus is a bargain. Unless I need to go where mass transit or cabs don't, or I need to have cargo, driving is my last choice. Once a month trips to Target and a weekly trip to grocery and I am good, no need to turn the key at all.

Hopefully I will stay this way until I am too old to walk.

David

I would think the slowing of suburban sprawl and the further urbanization of the country would impact this significantly. As people move into cities they drive less and thus reduce the miles drove.

econobiker

#25 PaulRino has some good points.

Also you can add that technology with instant /text messaging, video chat, etc has made it so that teens don't need to hang around to communicate. Gone are the days of a one phone line home...

Joseph Hale

I moved to the east coast to escape the financial hassle of car ownership. The premium I pay in rent and taxes is more than balanced against what I save on gas, insurance, tires and repairs. Though I doubt many others take their dislike of automobile society so far, I know the sentiment is not uncommon among my generation, who grew up with badly-made cars and the parade of surprise costs that accompanies.

Lan Sluder

Although there are doubtless many factors involved, I'd be inclined to partly credit the aging of the U.S. population. The median age is now almost 37 years, compared with about 33 in 1990 and 28 in 1970.

Studies show older drivers make about the same number of auto trips as younger drivers, but the trips are shorter, so they drive fewer miles.

The number of older people in the U.S. continues to increase dramatically. The 65+ population increased by about 15% from 2000 to 2010, and it's expected to increase another 35% or so from 2010 to 2010.

--Lan Sluder

Mojo Bone

I thought it was because we ran out of parking spaces.

Haskins

Has anyone considered these contributing factors:

1) There have been at least 40 million abortions since Roe v. Wade in 1973. The majority of these babies would have become drivers if they had been carried to term.

2) Many 20- and 30-somethings are delaying marriage/having children longer than previous generations. Those that do have children often have only 1 or 2 children, compared to the larger families in previous decades. In other words, the population growth is almost stagnant.

3) Illegal immigrants in the US, estimated between 10 and 30 million, are far less likely to apply for driver's licenses, than legal residents. Are there any statistics on their contribution to person miles traveled?

David Starr

Could it be that cars just are not as cool as they were in my generation? None of my children much cares about cars, car shows. auto racing, or doing car maintenance. When they want to show coolness to their peers, they point to their hand built computers, not their hot rods. Of my three driving age children only one currently owns a car.

Emmi

Dare I hope it's also due to a growing awareness about pollution and habitat destruction caused by roads? More likely it's the causes listed in the comments and article, but environmental issues may have given biking a boost.

I'm honestly astonished by the number of people I know who have decided to take their bike to work, and I'm not talking about in California. I'm talking about where I live in New England. Yes, winter bike commuters.

I saved an outrageous amount of money during the 2 years I lived without a car.

Joel Upchurch

I don't know what was happened earlier in the decade, but I suspect many people are driving less because they don't have a job to drive to.

What is more remarkable is that the fatality rate per passenger mile has dropped 25% during the last decade. The fatality rate is 1/5 what it was 50 years ago.

http://www-fars.nhtsa.dot.gov/Main/index.aspx

aaron

You forgot to include cellphone use adding to congestion.

aaron

By increasing following distanced (ie, decreasing road capacity).

And by distracting drivers at bottle necks, decreasing thoughput and decreasing road capacity even more (the distracted driver may make up the distance with more acceleration, but the cars behind won't).

not my real name

Gas at over $3.40 a gallon and you ask why we don't drive More what planet do you live on.
I hardly ever go to the bank any more I just use electronic transfers. Why drive 14 miles round trip when people drive like idiots and I don't want or need a accident. .
Also I buy a lot when i food shop about every 10 days for a shopping trip eliminating gas waste..