The Traffic is Falling

Published at the CTS Conversations Blog as Why are Twin Citians taking fewer trips?

The latest summary of the Twin Cities Travel Behavior Inventory is out, and it says the total number of trips in 2011 is lower than in 2001.

This is consistent with a lot of evidence we have been seeing from various sources on “Peak Travel”. Nationally, passenger miles on highways traveled today is lower than 1999, and miles per capita lower still. This is in stark contrast with the trend from 1900 to 2000, when vehicle miles traveled increased almost every year, with a few exceptions due to economic downturns or energy shocks. Why might this be? There are a number of hypotheses:

  • Employment – If fewer people are working, fewer people are traveling for work, and fewer discretionary trips are made by both workers (nervous about spending money) and the unemployed (who have little or no money to spend). Unemployment increased sharply beginning in 2008, and though it has declined, employment participation are still much lower (hovering around 58.6% of the population, down from 62.7% for the period before the recession). Demographics are part of this, and many people have just dropped out of the labor market, as their skills have been devalued by the economy, and either chosen early retirement (if near retirement) or deferred entry into the workforce (if young). The rise in female labor force participation from the 1950s through the 1990s has run its course, as labor force participation is roughly at parity by gender.
  • Gas prices – The price of fuel increased sharply in the run-up to the Great Recession – and this certainly discouraged car travel. Interestingly, it also reduced car crashes by more than the reduction in VMT, which we attribute to worse than average drivers (especially the young) being more likely to be priced off the road.
  • Changes in driver license regulations – It is harder for young people to get drivers licenses, and less valuable since they now need more supervision. More defer licensure and auto acquisition.
  • Social networking – It is now easier to virtually communicate with friends, in real-time and asynchronously, where-ever you are, so it may be less necessary to actually visit them. Time online just continues to rise, especially mobile.
  • At home work – Telecommuting continues to rise, more as a complement to office work than a substitute (check your email when you get up, check your email before bed), but even as the occasional substitute, so I can work from home either sometimes or regularly.
  • At home shopping – The rise of online retailing allows us to substitute delivery for fetching, and reduce the amount of shopping trips.
  • Kids today just don’t like cars – The culture just may be different, and the desire for mobility, especially auto-mobility has dropped, as kids would prefer to spend their disposable income on the latest internet-connected gadget.

There may certainly be other explanations as well. No one of these explanations is the whole story, and some are certainly more likely than others, but they all work in the direction of reducing auto travel. Importantly, travel by other modes has not made up for the large drop in car use. While transit, e.g., is up nationally due to the large investments in rail lines, that 20% increase in transit use in the decade is a little more than 1% of the 20% drop in passenger miles by motor vehicles.

Colleagues (Jason Cao, Yingling Fan, Michael Iacono, Greg Lindsey) and I have a study currently underway, Travel Behavior Over Time, with support from the Minnesota Department of Transportation and the Metropolitan Council to examine not just the top-line number, but what goes on underneath. We plan to determine the factors that explain travel demand and see if they are the same as in previous decades. We hope to understand whether the factors are the same, but the conditions are different, or whether underlying travel preferences have changed.

2 thoughts on “The Traffic is Falling

  1. Good stuff. But unemployment percentages is going to give an inaccurate view because when folks stop looking for work they aren’t counted in the unemployed. A better view is workforce participation. Looking at how many people are in the twin cities workforce from then to now, even with a same or smaller unemployment number, you could have a smaller workforce now because even more people could have stopped looking for work (disability, etc.)


  2. On the demand side these hypotheses seem reasonable, but the supply side does not seem to be addressed by these hypotheses, nor are costs adequately addressed.

    For example, large investments (relative to the number of users) have been made in rail transit over the past 20 plus years (much of it diversions from the Highway Trust Fund). While users may pay a small out of pocket cost relative to the cost of service, the cost in travel time for transit users is higher than for personal autos. Your Access to Destinations shows this.

    At certain costs – whether time or out-of-pocket – some trips are just not worth it. The same demand may be there, but the costs have been shifted through transportation policies. Diverting funds raised from one mode (autos) to another (transit) is certainly a shift in the costs and should change the VMT in a negative direction over time.


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