This idea was inspired by the "Estimated Parking Space Departure Time Display" idea. In fact, *this* idea is what I thought that idea would be.
Basically, start with a system which keeps track of when a car enters or exits each spot, and creates a statistical model of how long each car is likely to be there.
Then, whenever the lot is full, displays near the entrance the statistical likelyhood that at least one spot will open up in the next 5, 10, or 15 minutes.-- goldbb, Dec 17 2009 The original idea Estimated_20Parking...re_20Time_20Display [goldbb, Dec 17 2009] What level of uncertainty are you willing to accept? Will it also calculate your chances of bring the person who actually parks in that next spot, or just the likely window when someone else will get to park?
I think a sign that lit up saying "not today" when the lot was full would be more likely accurate than any other mechanism. A stopped clock right twice a day.-- WcW, Dec 18 2009 Thanks for articulating the secondary notion. I think this has been addressed in ideas in this category.-- csea, Dec 18 2009 I think this is how it works, or how it should work: If you have a parking lot of ten spaces and they are all occupied, the sign displays full. But if you have a hundred places, all occupied, the chances are that one of those places will be vacant pretty soon, say within the time it takes you to drive to the empty spot. If you have a parking lot with 500 places there will allways be an empty spot or a spot emptying as it were and the sign can allways read: spot available. Anyway, that's the trick I use with 21 billiard tables.-- zeno, Dec 20 2009 Exactly... the bigger the lot, the more likely that one of the spots will open up in the next few minutes. Furthermore, the shorter the average time that people are parked, the more likely a spot will open up in the next few minutes.
So if the lot is small, and the average time that each car is there is a few hours, then the sign might say, "Odds of an open parking space within 15 minutes: 1%", and if the the lot is big, and the average time that each car stays is short, it might say, "Odds of an open parking space within 15 minutes: 99%"-- goldbb, Dec 20 2009 random, halfbakery