The Butt Ugly Weblog

New Year's Rant

The house body (I live in an apartment) decided that people drive their cars too much and too fast on the walkways. They're the only way to drive close to the doors, so obviously people who need to load and unload stuff use those all the time. I sympathise with this; I have kids and sometimes people drive just too fast for my comfort out here.

The mistake happened when they decided to install gates on all the entrances to the walkways. Gates in general are a bad idea because their use pattern is

1. Drive to gate
2. Step out of the car to open the gate
3. Drive through the gate
4. Step out of the car again to close the gate
5. Drive to door, unload
6. Drive to gate
7. Step out of the car to open the gate
8. Drive through the gate
9. Step out of the car again to close the gate
10. Drive away

The problem here is that it relies on people to remember and bother to actually close the gates. If you don't close the gate, the sequence becomes

1. Drive to gate
2. Step out of the car to open the gate
3. Drive through the gate
4. Drive to door, unload
5. Drive away

This is a lot simpler to do, with the added bonus that if you load/unload a lot, you'll save a ton of time if you conveniently "forget" to close the gate all the time. Like the maintenance people, for example.

So, here's a deceptively simple-sounding math problem:

• Assume that for any given person A the probability of closing the gate after using it is p=0.3, if the gate was closed when he first came to it.
• Assume that for the same person, the probability of closing the gate is p=0.01, if the gate was open (people rarely close the gate if it's open already)
• Assume also that there's an elderly person B who closes the gate once per day, if it's open, huffing and puffing about gates and how nobody ever closes them
• Assume 50 users of the gate per day

What is the probability of the gate being open at any given time?

My empirical study suggests that it's somewhere near p=0.99... That is, out of the five gates we have, only one is ever closed. And that's the one very few people use.

OK, so gates are a bad idea because they assume that people will co-operate on something that's actively annoying for them. So what's the solution? Speed bumps. They cannot be turned off, and in general the incentives work towards remembering them - because forgetting about them is not convenient and may damage your car.