The Decline of Carpooling

The New York Times had an article recently about the decline in carpooling titled ‘Once Popular, Car Pools Go the Way of Hitchhiking‘.  I think the biggest issues here may be the title and the timing, since carpooling has been declining relative to vehicles driven alone.

Here’s the basic facts that the Times uses (though their maps are much nicer).

Year Percent Drive Alone Percent Car Pooling
1980 64% 20%
1990 73% 13%
2000 76% 12%
2009 76% 10%

Let’s begin with timing.  Wasn’t the time to write this article about 15-20 years ago?  Things clearly have changed since the 1970s – driving and owning a car has become generally more affordable.  The NY Times, to their credit, include data from the Texas Transportation Institute that show a decline in average fuel cost from $6.11 in 1970 to $2.82 in 1990 (in 2010 dollars).  With continued expansion of suburbs and exurbs, the move towards single occupant vehicles might be expected.  And the biggest decline in carpooling came between 1980 and 1990.  There appears to be a continued eroding of carpooling (in percentage terms), but its much less than that initial drop.

Which brings us to the title.  Carpooling still represents at least 10 percent of commuters.  It’s pretty imprecise to compare that to hitch hiking.  Further, the NY Times looks at only 2009 data, which come from the American Community Survey (ACS).  As best I can tell, they use the single year ACS data for 2009.  The ACS is a sample of US households – starting after the 2000 Census, it replaced the old long form that 20 percent of US households filled out each decade.

The single year ACS data are likely to be the least accurate – they also publish three and five-year estimates – but the most current.  But more than accuracy, 2009 may have been a particularly bad year to look at commuting and carpooling, since there was this little thing that people have been calling The Great Recession in full swing.  The following table shows individual year estimates of travel from the ACS from 2002 to 2009.  Three findings are clear from this table.

  1. With minor exceptions, both carpooling and transit ridership has been on a steady, if not spectacular, increase over the last decade.
  2. But, this increase has not kept pace in numeric terms, though it has in percentage terms) with the increase in driving alone.
  3. In 2009, at the worst moments of the Great Recession, there was a lot less travel in general, but carpooling has declined relatively faster (in percentage terms).
Year Drive Alone Carpool Transit
2002 99,574,701 13,366,660 6,202,191
2003 100,416,861 13,483,102 6,072,316
2004 101,635,318 13,183,471 5,978,055
2005 102,458,267 14,200,426 6,202,014
2006 105,046,395 14,851,751 6,684,040
2007 105,954,656 14,487,532 6,800,512
2008 108,775,532 15,401,688 7,210,014
2009 105,476,045 13,916,694 6,922,424

The following table shows the percentages by how commuters travel. Note that the 2002 numbers are closer to 10 percent than the 12 percent from the Census data for 2000 – there are no national ACS data for 2001. The Census data were probably higher quality, so this may just reflect some inaccuracy in the data. And while this table shows general percentage gains in carpooling and transit over the decade at the expense of driving alone, you cannot put much stock in that because the total number of people driving alone is increasing.

Year Drive Alone Carpool Transit
2002 77.4 10.4 4.8
2003 77.8 10.4 4.7
2004 77.7 10.1 4.6
2005 77.0 10.7 4.7
2006 76.0 10.7 4.8
2007 76.1 10.4 4.9
2008 75.5 10.7 5.0
2009 76.1 10.0 5.0

Back to timing for a moment. This past decade has seen carpooling remain a real mode of travel to work for 1 in 10 commuters. Perhaps that’s not as much as we would like, given congestion in the U.S., but it is not the type of decline the article suggests. The decade also saw an increase in transit use, which did not decline as fast as some of the other modes of travel in 2009.

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Is Population Growth Slowing?

I had to reach back a bit for this one, but this is one of the things that gave me the idea of writing this blog.  It’s a blog from New Jersey Future (who I like), and it looks at how population growth is changing from one Census to another, with a focus on New Jersey.

The article, Population Growth Slows in NJ, Nationally, claims that “the country’s rate of growth in the 2000s — 9.7 percent — is its slowest rate of growth over a decade since the Great Depression (the US population grew by only 7.3 percent in the 1930s)”.  To be fair, NJ Future is not the originator of this idea, but I read them regularly, so it’s where I picked it up.

This is a classic case of comparing rates of change where the base varies too substantially to be meaningful. Looking at the chart below, the U.S. actually added the third most people in a decade since 1910 and 2000 to 2010 is essentially equivalent to 1950 to 1960 (second most). Only 1990 to 2000 stands out above all other decades.

Turning to New Jersey, the first decade of this century showed relatively less growth than in the past. The following chart shows how the NJ population changed – in absolute numbers – for the Garden State. New Jersey added about half as many people from 2000 to 2010 than from 1990 to 2000. The 2000 to 2010 growth was about 100,000 fewer people than the average of the past 10 decades. Comparatively, the U.S. as a whole added almost twice as many people from 2000 to 2010 than the average of the past 10 decades.

Once again, its easy to look at a percentage and come to false conclusions. From an urban planning perspective – and New Jersey Future is an urban planning blog – decisions are impacted by numbers of people, not growth rates.

The original post also includes a Census map showing the percent change in population by state. I’ve reproduced that map, along with a companion map (on the right) showing actual change in population. A simple comparison illustrates how misleading percentages can be. Nevada grew 35 percent between 2000 and 2010, while California grew by ‘only’ 10 percent. This suggests that Nevada grew 3.5 times faster than California, right? Not so fast. California added 3.4 million people, while Nevada added 700,000. California added almost 5 times as many people in last ten years than Nevada. And while California is clearly a larger state, those people still require infrastructure and services, as well as contributing to the economy of the state.

You can click through to the Many Eyes Visualization below and look at any decade – you have to change both maps though.

State Population Growth 2000-2010 (pct on left, num on right) Many Eyes

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