My post yesterday on why teenagers don’t have drivers licenses continues to generate discussion (thank you readers!). I’m going to continue the discussion here.
Despite the poor economy and expensive gas, Americans still love their cars. This love goes way, way back to the invention of cars (see my other blog post on super-highways). Here are some other interesting figures about Americans and their cars.
There are more cars than licenses drivers in the US. This is not a recent trend: there have been more cars than drivers since 1971. This gap is getting smaller, but it’s still wide, historically speaking. My husband pointed out that commercial and government vehicles may be included here. Another report shows that cars outnumbered drivers c. 2000.
This figure shows the miles of road (red). More recently, the total number of lane-miles (green) are shown, which takes multi-lane roads into account. This is a bit misleading, since adding a second lane does not double the road capacity. Compare the total number of road-miles to the total number of miles driven (blue). This suggests that there may be a road shortage. However, building more roads only encourages people to drive even more. Still, Americans love to drive more than ever.
The average annual number of miles driven per driver has steadily increased over time. Only recently people have been cutting back on their mileage, probably due to a poor economy and expensive gas. However, we have only cut back to our 1998 driving level.
Look at the purple line here. This is the average mpg relative to 1987 cars (the 1.0 level), and low is good. This shows that the average mpg has been more or less constant since 1980. This is largely because of the growing popularity of SUVs and minivans. We’ll have to see if the trend of tiny cars and Cash For Clunkers improves these values in the future.
Car, light truck (read: SUVs) and motorcycle fatalities per mile driven. This should convince you not to get around by motorcycle! You cannot see the car fatalities rates well. The fatality rate on rural rates is more than twice as large as the fatality rate on urban roads. This is probably due to urban congestion (congestion = slow driving = safer accidents) and the danger surrounding 2-lane rural highways (2-lane highways = head on collisions at high speeds). Both rural and urban fatality rates have come way down since 1980, probably due to air bags and other safety features (and despite of road rage). The urban fatality rate has dropped faster than the rural fatality rate. Again I would suspect urban congestion here. This is the upside to traffic. Takeaway: Driving is safer than ever.
Punk Rock Operations Research 
July 25th, 2012 at 9:52 am
Really interesting stuff. Traffic has fascinated me for a long time. In fact, trying to understand traffic patterns is what first got me into OR.
I don’t know that I have anything to add to the discussion, but I’ve been enjoying the posts. Thanks for the read!
July 25th, 2012 at 9:59 am
Interesting stuff. Makes me think my response to yesterday’s post is more legit, that teens were probably driving more up til a certain point and just saw a drop recently. Although I do think that more regulation around teen driving could also be a factor.
July 25th, 2012 at 10:42 am
“… adding a second lane does not double the road capacity.” It comes pretty close some places. See, for instance, the Long Island Expressway (a.k.a. “World’s Longest Parking Lot”).
Regarding your comment about Americans loving their cars, this love (or, more precisely, the prevalence of drivers licenses that goes along with it) has been sited by some historians as our “secret weapon” in World War II. A considerably higher proportion of military-age males in the US knew how to drive than the corresponding proportion in European countries (particularly Germany), which helped the US Army make better use of truck transport, and thus move faster, than the Wehrmacht (who were still relying to some degree on horse-drawn transport).
July 25th, 2012 at 11:12 am
“Compare the total number of road-miles to the total number of miles driven (blue). This suggests that there may be a road shortage.” Bear in mind that speed limits on highways increased during this time span. That allows more road miles driven per physical road mile. I don’t know if it accounts for the entire increase in the gap, but it likely accounts for part of it.
July 25th, 2012 at 3:48 pm
@prubin73 This is true up to a point. I’ll blog more about that later this summer, so stay tuned.
July 25th, 2012 at 11:50 pm
Would love to see some additional international comparison.
I remember that in the EU, fatalities have drastically declined since 1980. I can’t find the stats, but comparing GER and USA in https://en.wikipedia.org/wiki/List_of_countries_by_traffic-related_death_rate is shocking (also: http://de.wikipedia.org/wiki/Verkehrstod#Deutschland).
@Paul I remember reading that the average commute in the US has doubled in the last 20 years. Not sure how accurate my recollection is (google is failing me).
July 26th, 2012 at 4:18 pm
@Peter: It would not shock me if the average US commute doubled in time over the past 20 years. About 40 years ago, when I lived on Long Island (suburbs of New York City), there were many commuters (both rail and passenger car) into the city western and central Long Island, parts of Connecticut and parts of New Jersey, but from eastern LI there were fewer commuters and most of them took the train to avoid the long drive. Perhaps 15 years later, when I helped an about-to-be-ex-girlfriend move to New Jersey, there were masses driving from eastern Pennsylvania to New York City (going across the width of New Jersey), which shocked me.
I keep waiting for telecommuting to start reducing commutes.