Interesting Question of the Day – 6 December 2017

When driving down a motorway, Dennis the Driver hits the brakes suddenly before accelerating and continuing on his way.  The driver behind him also slows down, as does the driver behind him and so on.

How fast does this phantom traffic jam move backwards down the motorway?

The first new player to comment on the website within 5km/hr of the correct answer wins a free drink at their next iQ Trivia show.

Tagged with: , ,
4 comments on “Interesting Question of the Day – 6 December 2017
  1. Nathan says:

    Well, assuming the motorway is a 100kph zone, and everyone is driving at a safe stopping distance for an average reaction time (42m and 1.5 seconds), I come up with a speed of 100kph for the traffic jam concertina.

    (42m per reaction)
    (40 reactions per minute)
    1.68k per minute
    60 minutes*1.68k = 100.8kph

    • iqtrivia says:

      Going backwards down the highway at 100km/hr?

      Not quite. It’s been tested and it’s considerably slower than that.

  2. Luke says:

    I think QI covered this in an episode and it was around 15kms? Can’t remember the math.

    • iqtrivia says:

      Our sources says 20km/hr, but 15 is pretty close.

      Also, this video explains traffic pretty well (and proposes solutions.)