June 17, 2009

Sprawl, 1

I have no idea when suburban sprawl is supposed to have begun -- it's a catch phrase that encompasses lots of changes, so let's focus on just one of them and see when the shift occurred.

Going through many versions of the Statistical Abstract, which collects the data from the Federal Highway Administration, I made several graphs of the average number of miles traveled per vehicle. The longer the distance that you typically drive, the more sprawling your environment is, right? The car and bus data go back to 1940, and although it's spotty during the '40s, it's complete from 1949 to 2006. The van / pickup / SUV data, and the "all types" data (with the van / pickup / SUV included), only go back to 1970. Here they are (click to enlarge):

Aside from a sharp dip during WWII, the average distance traveled by cars remains remarkably constant from 1940 to 1980. Afterward, though, there is a steady increase, so that we now drive 3,000 more miles per year than we did in 1980. Again excepting the WWII period, distance traveled by buses has declined fairly steadily, although there was a slight rebound during the '80s and '90s. I don't know if this is because there are simply more buses, so that each one needs to travel less in order to serve the customer base. There are also data on total vehicle-miles traveled by vehicle type, but I'm not going to schlep through all those PDFs again just to find out. Er, what I meant to say was that the resolution of this open question is left as an exercise to the reader.

As for vans and pickups, the distance they travel increased from at least 1970 through the early '90s, but then decreased after. Accounting for all types of vehicles, we see again that it looks pretty flat before 1980 and increases steadily afterward.

There are many ways to measure "suburban sprawl," and I'll look at some others sometime soon. But at least for "having to drive longer distances," it looks like sprawl hit all of a sudden around 1980. I don't know what happened beforehand that would've caused the shift. It's not a cyclical pattern like crime, where we don't need to point to causes right before crime started going up or down (it does that because it's cyclical). It's pretty clearly stable for 40 years, and then turns steadily upward.

If you have an idea, include references or links to data that support what you say. I could list 500 potential causes, but without anything to back it up, why would anyone care? For example, if fuel prices are supposed to be the cause, dig up some data or provide a link to someone else's graph of fuel prices (adjusted for inflation) over the past 50 to 70 years.


  1. Interesting post. One data point that correlates with this is total credit market debt as a % of GDP. It starts rising dramatically around 1980 or so and shoots up pretty substantially to the present. It's rise is concomitant with that of the financial industry's which grew starting in the 80s to become the behemoth it is today.


    It wouldn't surprise me if the huge expansion of debt starting in the 80s is tied to sprawl. Real estate development is heavily dependent on massive debt finance. And we now know how much debt was required to finance not just suburban houses further and further away from cities but the entire lifestyle of replacing large cars every two years, home appliances, large home entertainment centers and electronics, granite counter tops for the wife, kitchen remodelling every 3 years, etc.

    We know that a lot of this debt that was expanded since 1980 was blown on the housing sector. Trying to finance as much sprawl as possible, reaching out into the "exurbs."

  2. One thing you can notice about suburbs around major cities is that you can date suburban neighborhoods based on what the houses look like, and how far they are relative to the city center.

    agnostic, you lived in the Wash DC metro area, so you probably have an idea of what I'm talking about. the first suburbs built around DC after WWII in the 40s/50s were places like Silver Spring, Arlington/Falls Church. These suburbs are pretty close to DC and the houses are pretty modest. Then slightly further out and built in the 70s you have suburbs with different architectural styles than the immediate postwar suburbs. You get "rambler" or "ranch" style houses. And then starting in the late 80s you get these suburbs like in the western part of Fairfax Co. that are really getting far from DC (25 miles+) with larger, McMansion style houses.

    This probably doesn't match perfectly with the sprawl driving figures, but they don't seem totally unrelated either.

  3. Sprawl is primarily whites fleeing from non-whites.

  4. I haven't done the exercise for the reader of looking at total miles travelled. However, I did check out the average number of cars per household.

    It has grown greatly, making the increase per vehicle even more significant.

    Examples: Massachusetts has seen the number of dwellings with two cars grow from 6.7% to 17.8% from 1960 to 2000. [Ref]) Australia (my home) has seen average cars per dwelling grow 10% since from 1986 to 2000. [Ref]

    I pondered whether the demand for more driving was merely that the supply was limited by the number of cars per household, and that cars have become more affordable.

    I don't have any car affordability prior to 1980 [Ref].

    However, I realised that that might help explain the jump in the number of vehicles, it doesn't explain the increase in miles per vehicle, so I am at a loss.

    Gasoline affordability jumped in 1985 [Ref] but that comes too late to explain your graphs, and doesn't explain why they didn't drop the same amount when gasoline affordability dropped again.

    In conclusion: I got nothing, but at least I have the data to be sure of that. :-)

  5. I suspect sprawl was ongoing from the end of WWII, but something involving the increasing number of cars per household held the miles per flat until 1980. I presume that women entering the workforce drove up the miles driven per car as women started commuting more.

    Consider an imaginary couple that lived in an inner suburb in 1960, and had one car, which they put a fair amount of miles on -- e.g., he drove it to work during the day and she drove it to shopping in the evening and weekends.

    In 1970, they move to an outer suburb. His commute goes up, and now she buys her own car to drive the kids around. But, their miles per car stays flat because she doesn't drive all that much.

    In 1980, they move to an exurb, and his commute is even longer, plus now she re-enters the workforce, so she begins commuting too. Miles per car now goes up.


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