Sunday, June 20, 2010

The Proximity and Lateness Rebound Effect

I have a habit of labelling any unintended consequence that works in the opposite way to the intended consequence as a rebound effect. With this in mind, I hereby declare the discovery of the Proximity and Lateness Rebound Effect.

The discovery is not mine of course, but the name is. I learnt of this bizarre social phenomenon here.

The Proximity and Lateness Rebound Effect (I would appreciate any better name suggestions) describes the offsetting behaviour of people to commuting distances. One would initially think that moving closer to their workplace, their relatives, friends or other regular destinations would reduce lateness, but in fact the opposite effect can potentially occur – as your commute decreases your lateness increases (in frequency - you are late more often).

Here’s my proposed theory as to why this may occur.

First, 100% punctuality is surely suboptimal.  Because each trip has a degree of uncertainty, if we budgeted for perfect punctuality we would have to allow for a commuting time under the worst circumstances every time.  We would be far too early most of the time just to ensure that we weren't once a minute late.

Now suppose that being a little late is not a big problem, but being quite late is a serious problem. We might say that we want to be less than 10 minutes late 70% of the time, and less than 20 minutes late 95% of the time.

If your commute is typically 50mins, but traffic congestion and delays mean that the trip takes less than 70mins 95% of the time, less than 60mins 70% of the time, and less than 50mins 50% of the time, you can budget for a 50 minute commute and meet your lateness expectations. You will be on time 50% of the time, more than 10mins late 30% of the time and more than 20mins late a mere 5%.

If instead your commute is a mere 10mins on average, with only a very small variation in time (say less than 2 minutes), and you budget 10mins for your commute you will far exceed your lateness requirement. Therefore you may start allowing less and less commuting time to get to your destination, and soon become accustomed to regularly being a little late, but never very late.

Because of the difference in trip variation, the person with the long commute needs to be more cautious to avoid being exceptionally late. Doing so increases the frequency that they arrive early. On the other hand, those with short commuting distances have very little chance of being extremely late, and therefore need to pay little attention to factoring in their commuting time and may regularly be a little late.

My personal experience of moving closer to work is just this. I almost treat the 10 minute commute as negligible, and am typically a little late to everything. Previously, when the commute was about 30 minutes I would ensure that I had budgeted enough travel time, with a little room for delays.


  1. I've read papers on Lateness and some have come to conclude that Late Arrivals are inhibited folk; fear on sitting there alone, when no-one will come to talk to them (maybe). Take that from the equation by arriving late. So it might be said that it isn't about time management, rather psychological, a worry of being left out. Come late and simply fit in. On the other hand lateness might also mean a deep thought, take as much time as possible to think about the the next step. Unless penalties occur, leaving things as late as possible may reap benefits. Further, boarding a bus - last-on=first-off (closer to the door), and so on.

    If a train runs every half hour and it takes 20minutes to get "there" you're likely to be 10minutes early or 20minutes late. After a journey or two you'd work it out, it's not rocket science.

  2. Totally agree. When I lived in Canberra, the door-to-door commute was around 10 minutes with very little variation (Canberra is a driving paradise), yet I was always around 5 minutes late.

    Then I moved to Melbourne and started catching the train. Due to its unreliability, I always left a time buffer and was rarely late. Now I ride my bike and, because it is reliable (not much time variation since I travel along bike paths), I am late less often in Canberra but more often than the train. Go figure...

  3. I suspect this is more about the variability of your trip time than the length of the trip. A shorter trip usually has less variability than a long one, but other factors (like whether you are walking or have to catch an unreliable bus) probably have more of an impact.