Saturday, November 21, 2009

How we move: Transportation surveys

There have been a number of articles in the paper recently related to the upcoming census.

One was on how a local coalition of groups that serve the the Hispanic community was urging cooperation with the census. Some Hispanic groups are urging a boycott because they feel the US government is too slow to change immigration policy. Many individuals fear cooperation because they are in the US illegally, despite guarantees that the data is confidential.

Another article reported how gay and lesbian couples will be counted differently in 2010. This year they will be given the option of checking "married" as well as "unmarried partner."

Both articles emphasized the importance of an accurate count of the demographics represented. If the decennial count under or overestimates a group, it can have consequences for federal funds flowing to an area. But the census is also the best count of how we live and who we are. How many are young or old; married, divorced, partnered, or living alone; poor or rich, working or unemployed; homeowners, renters, or homeless; well-educated, students, or illiterate? Where do we live? How has population shifted?

For people study transportation and mobility, the census is also the way we define the importance of how we move around. But it only asks how you get to work - which is a small percentage of daily trips - and the census is taken the last week of March, not a walking and biking friendly time of the year in Wisconsin. It also asks what your "primary" transportation method to work is the previous week. If you biked one day, took the bus one day, got a ride to work one day, and drove by yourself two days, it might show up as "driving alone" on the census, although you used other methods three out of five days.

And what if we have a horrible snow storm or pouring rain that week? I'd probably be on the bus instead of my bike. Others might drive instead of walk.

So the census is often a poor measure of how we move around, but it's what we have. There are other surveys, such as the American Community Survey (ACS)- which randomly asks a subset of the population for information each year, or the National Household Transportation Survey - which asks about all travel, and not just work trips.

On the other hand, if you look at any of these surveys, Madison still has a much higher percentage of people walking or biking than most areas of the country. For the city of Madison, in 2008, the ACS shows the mode split for people over 16 years old (131,507 people) is:
  • drive alone: 65.4%
  • car pooled: 9.8%
  • public transportation: 8.4%
  • walked: 8.5%
  • other means (I guess this includes bikes): 4.6%
  • worked at home: 3.3%
If you add all the non-car based categories, you have 21.5% of people that travel for work getting there without using a car. (I'm not sure whether taxis are included in "other" or "carpooling," since that's not included in public transportation.)

The percentages for the nation as a whole broke down like this:
  • drive alone: 75.5%
  • car pooled: 10.7%
  • public transportation: 5.0%
  • walked: 2.8%
  • other means (I guess this includes bikes): 1.8%
  • worked at home: 4.1%
So for the nation as a whole, the percentage of people getting to work without using a car is 9.6%.

It will be interesting to see how the numbers change for 2009. I ended up being one of the people surveyed, which piqued my interest. Did the gas prices in 2008 push people to drive less? Will driving bounce back? Have the improvements in biking facilities changed that "other" category?

We'll see.

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