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Let me bend your ear for another couple times about this NHTS data, today I’d like to share a discussion of age and modes.  I started this series wanting to look into the structure of the decline in traffic vehicle miles travelled.  I want to know what was going  on, and thankfully the NHTS has been tracking traffic, transit, walk and bike trips periodically since 1995.

NHTS collects age data on people taking trips more conscientiously than it does trip purpose or trip length, so this was a pretty easy analysis to do.  I just had to make sense of 7,000 lines of results.  Its all my poor laptop can stand.  If I ever write about trip purpose, know that I have restarted the spreadsheet without calculations, and that I have figured out how to bypass a lot of incomplete data.

This will be a mostly graphic and population explanation of what’s going on in transportation throughout America.  To start, look at the age distribution of the US in 1995, 2001, and 2009.  I didn’t do anything more sophisticated than multiply the census age distribution by the straight growth rates between 1990, 2000, and 2010, and binned the deadly 16-17 and slightly less deadly 18-24 age groups to match the NHTS.

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Of course, this shows the “Baby Boomers” aging from their late 30s to their early 50s.  Keep your eye on the Blue, Green, and Red Lines for 1995, 2001, and 2009 in the next graphs. They show changes in transportation per person in each of those age groups. 

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Here’s total trips, showing a dip in early adulthood and rise in mid adulthood.  1995 was peak travel time for the parenting years.

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Here are trips under 4 miles.  Note that the scale for this one is half of the previous graph.  Basically the same pattern as before.  The important thing about this half of the trips is that they could be taken on a bike, if America woke up and felt suicidal one morning.

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The scale has halved again.  A quarter of all trips, same pattern. Here showing the trips that are firmly in the range of biking, not walking, traffic, or transit.

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Here the scale is about a sixth of the original, showing all trips that could be walked.

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I kept the scale the same here, to show what fraction of those trips that could be walked are being taken in traffic.

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The above scale is 1/10 of the original, showing all walk trips.  Note the significant increase in walking trips between 1995 and 2009.

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Of course, most of this trips are a mile or less, and the pattern stays consistent.  Americans are walking more now, especially in middle age.  The “millenials”, however, are not walking as much as they did in 2001.

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Looking at transit trips, the scale is now 1/50th of original.  A lot of Americans never take transit because it is nowhere near them.  Many more don’t take it because it doesn’t connect where they live with where they work in a timely fashion.  And of course transit is often built to serve the home-work trip in reaction to traffic congestion, so its audience is necessarily going to be limited.

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At 1/100th the original scale, biking is rising for middle ages, but actually falling for the youngest “collegiate” ages.

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The pattern holds for all trips under 4 miles.  I am not sure if the bottomed out results are collection/reporting errors, or actual inactivity.

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For bike trips between 2-4 miles, the pattern gets messy from age to age.  The numbers are tiny, but they might show biking picking itself up off the floor from 1995.  The pattern is similar for trips under 1 mile.

Monday, I’ll write a bit about parking, shared in time and space.

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