Thursday, September 15, 2022

Empirical evidence for Murphy's Law

I live in a cul-de-sac in the Marylandian suburbs of Washington, DC.  In order to drive from my house to the main street in the area, I have to drive three quarters of a mile and take three right turns in my neighborhood's streets.

The neighborhood itself is made up of single family homes - each one with its own driveway and two-car garage.  Assuming that most people have their garage full of junk, there's ample space in their driveways for two cars to park and be off the street.

One of the planet's smartest minds is Malcolm Gladwell, who has eloquently discussed the 10,000 hour rule for becoming an expert at anything. He discussed this in his amazing book “Outliers.” As Gladwell tells it, the rule goes like this: 

It takes 10,000 hours of intensive practice to achieve mastery of complex skills and materials.

I've somewhat adapted the rule to gather 10,000 points of data for an interesting experiment.  Here how it started.

I moved into this house in 2009.  Soon afterwards I started to notice an interesting and baffling series of curious events whenever I drove away from my house towards any destination (or the return trip) - for the first 3/4 of a mile they're nearly always the same. Or when I enter the same entry point (from the main street towards my house) and drive home. In other words, a round trip.

The streets leading to the neighborhood exit are mostly clear of parked cars, as nearly every house parks in their own driveways.  Households with more that two cars do often park on the street, as do visitors, etc.  Whenever a vehicle is parked on the neighborhood streets, it essentially blocks that side of the street, forcing any traffic on that side of the street to have to use the oncoming/other side of the street to continue on.

The neighborhood also has a lot of "regular" street walkers (not hookers), dog walkers, and runners, and car traffic is generally very light.

Vehicular traffic is generally very light in the neighborhood - usually only the people who live there, delivery vehicles, visitors, and garbage and/or recycling trucks.

A few months after we moved in, I noticed that there seemed to be a higher incidence of the following scenario... that one would expect statistically.

The scenario is that the incidence of two oncoming vehicles "meeting" at the spot where one side of the road is blocked by a parked car appeared to be weirdly tilted towards a Murphian dictate of events.  

Add to that the odds of the random dog walker, stroller or runner, a parked car and two oncoming vehicles meeting at precisely the worst spot on the streets from my house to the neighborhood exit, and my curiosity was kindled.

And thus, I started to keep a log in my car - using a calendar book - to record these instances of two cars, driving towards each other, meeting at the narrowest space created by a third car parked on the street.

A few days ago, my 10 thousandth drive took place - about 12 years or so of trips, usually at random times of the day or night, and 12 yearly calendars full of data.

Of those 10,000 data points the following was recorded:

  • No oncoming traffic was met whenever a parked car blocked one side of the road 4,611 times
  • An oncoming car was met at the blocked spot (forcing one car to stop and wait for the other car to pass) 5, 389 times
  • Of that 5, 389 times, 2, 673 times, not only where there two cars meeting at the "blocked" spot, but there were also either walkers, runners or dog walkers in the same narrow area - thus making driving maneuvers even more complicated.

54% of the time that I drove from/to my home I came across an oncoming vehicle at precisely the one spot (in an otherwise generally open street) where there was a third car blocking one side of the road!

Under what statistical scenario does that make sense when there are .75 of a mile of streets which are 98% empty of parked cars (on the street)?