“All models are wrong, but some are useful.”
George E.P. Box
After reading how it works, it should be obvious that Parkroulette has several weaknesses that should cause you to doubt the accuracy of its results in certain ways.
- The results are only as good as the record of tickets maintained by the SFTMA. Occasional typos and missing values show that it is not perfect. I have not tried to determine how many tickets are completely missed.
- The reconstruction of patrols assumes that patrol cars drive thru the city in the way a normal car would. A patrol car is assumed to take the shortest path between two tickets in sequence.
- The number of tickets issued by on a patrol are assumed to be sufficiently frequent to approximate the "shape" of the patrol. For example, for a patrol to complete a triangular path thru the city, there must be at least 3 tickets isssued on the patrol.
- The cost calculations do not take into account the type of violations at an address. The cost is calculated as a simple average. If you park in a driveway, your ticket will obviously be different from someone who overstays a two-hour spot next to you.
- Possible tow-aways or "booting" are not counted in the cost.
- The chance of a ticket estimates assume that tickets are issued only by a SFTMA patrol. Tickets issued by police officers or by other means are not accounted for.
- Patrols are assumed to ticket both sides of the street at once. A patrol may in fact ignore one side of the street.
Contact us with your thoughts on these open questions.
“We must walk consciously only part way toward our goal, and then leap in the dark to our success.”
Henry David Thoreau
- Do patrols follow regular routes from day to day or week to week?
- How accurate are the chances of getting a ticket? Are they biased low or high? What would happen if we intentionally tried to get tickets? Would it happen at the predicted rate?
- How long does a car need to be in violation before it is towed? Or does somebody need to call it in?
- Are there secret spots that are never patrolled?
- Is there metered parking where it is cheaper to risk a ticket than pay the meter?
- What are the chances of getting a ticket for overstaying a two-hour parking zone? The chances are different for this calculation because the parked car must be visited twice by a patrol.