Figure 3: Histogram of parking time remaining, less than 60 minutes. Approximately six of these data
points are actually spill over from “paying” customers.
12 parking spots have been paid for at
any given time.
YES, BUT WHAT DOES IT ALL MEAN?
So in one sense, the distributions of
the data are irrelevant; there are 100
parking spots on average, and the average time that a parking spot is occupied
is some time greater than 27 minutes. If
we make the (not bad!) assumption that
the parking spots that run over are occupied for 90 minutes, then the average
occupancy is 43 minutes. In a lot with
100 spots, this means that on average,
A NA L Y T I C S
one spot comes open every 30 seconds.
This doesn’t sound so bad. If we treat
the system as a queue, and use the
(observed) steady state cars waiting of
three, we can place a rough lower estimate [3] that a new car arrives every
30 seconds looking for a parking spot,
and that they have between a 15 percent and 25 percent chance of finding
an open spot. These crude estimates,
however, do not agree very well with
observation, because they neglect the
“blocking” effect of other cars waiting
for spots to open up. A better analysis of
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