CoolData blog

20 July 2012

Bus driver math

Filed under: Off on a tangent — Tags: , — kevinmacdonell @ 2:24 pm

When a bus holding 50 commuters is forced to wait for 30 seconds for a runner to catch it, the runner has saved the 15 minutes it will take to wait for the next bus, but the total cost in time is 50 people x 30 seconds, or 25 minutes. By this math, the driver is doing the world a favour by stepping on the gas and leaving the runner behind.

I was taking the Number 80 bus to work the other day when an elderly woman got on. As we were pulling away, she realized she had left her bag on a bench at the stop. She got the driver to halt and got off. She took quite a long time to make her way back, and the driver waited for her — I think she was surprised, but she appreciated it.

This driver chose not to apply the math. And I am glad he didn’t. I suspect most people on the bus felt the same way. We were mildly inconvenienced, but people are reassured when they see public examples of compassion. Yes, we still live among human beings. (Even if drivers are trained to sometimes be lenient, which I don’t think they are.)

When I advocate a data-driven approach to making decisions, I am speaking of specific scenarios, not an approach to life itself or a way to rid ourselves of experience and human wisdom.

Don’t expect me to conclude with twaddle such as “the most importantĀ things in life just can’t be measured” or “numbers aren’t everything.” (Blech!) The quantophobes among us are all too ready to embrace the half-truths in those statements and deliberately mistake them for the entire truth.

I prefer to say that there are small things, and there are big things. Don’t forget the big things while you are busy optimizing the small things. Efficiency with details may not always coincide with the greater good.

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5 Comments »

  1. Try that on a New York City bus! :)

    Comment by Jeff — 20 July 2012 @ 7:03 pm

  2. Utility is not linear, and not additive for a group. Thus, a 30 second delay may be a little inconvenience to most bus riders, but a 20 minute delay after missing a bus could be a day wrecking experience for one person. Considering an aggregate utility function, the quantified solution may be exactly what the instincts instructed the driver to do.

    Comment by David Gonzales — 21 July 2012 @ 1:25 am

  3. I noticed signage in the Montreal Metro showing the yearly time/cost incurred by people who forced closing car doors open to jam their way in rather than wait 5-10 minutes for the next train. When you force the doors open it takes time to reset and then begin closing again. That and your post remind me of Charles Stross’ Rule 34 where driverless microbuses travel through the Edinburgh and if you want one to wait or to go off-route for pickup or drop off, you start a bidding war between you and the current passengers who don’t want the bus to be diverted. The bus adjusts to the highest bidder’s wishes. Market-driven bus routes :) Not exactly the commuting world I’d like (unless of course I was late, could see the #80 just pulling away and could bid 2x or 3x the ticket price to get it to stop).

    Comment by Greg — 21 July 2012 @ 8:53 am

  4. Still a pleasure to read you (even if no longer in advancement services). Had value-cost to society been incorporated into the 15 minutes vs. 25 minutes dilemma; I would like to believe that the data would have arrived at the same conclusion as common-sense would dictate.

    Cheers

    Comment by jsb — 26 July 2012 @ 12:44 pm

  5. I was thinking of this post yesterday, while sitting on a bus. None of the cars would let us merge into the lane we needed to be in. We had to sit still at the merge point and wait for several minutes before another bus came along in that lane and yielded to us (different but overlapping bus routes). Those car drivers were either not doing the math or were not interested in optimizing for the greater good.

    Comment by Jim — 10 August 2012 @ 3:44 pm


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