14 July 2010

Parking lots, self-interest, and risk

The section of the parking lot where I park at work is bounded on one side by a fence and on another side by a concrete wall. At the area where the fence and this wall come together at a 90 degree angle, there is a small opening that funnels everyone through a pedestrian gate--and you have to walk through this gate to get to the building. It is also important to note that the lots are very large, and do often fill up. So good parking spaces are coveted. Arriving late can mean a long walk.

While I typically arrive at work within the same 10-15 minute window, I have sometimes arrived as much as an hour or so later and often take interest in the parking patterns of people arriving for work (yes, really I do; sad isn't it!).

As you might expect, the earliest arrivals tend to park as close to the gate as possible, and then the lot fills in a rough, semi-circular arc from the fence to the wall. This would seem to support the notion that people's self-interest is walking as short a distance as possible to get into the building.

But there are exceptions to this rule.

Some people park farther off into the lot (or even the next lot), seemingly at random. I have heard some people express the notion that they purposely park further off specifically to walk further, for reasons of exercise. Ok, that makes sense, but it probably doesn't explain everyone who parks futher against their self-interest. Maybe people park further away, but closer to the parking lot exit anticipating an easier exit?

Between parking lots there are a small number of "street" style parking spaces. These spots fill up well in advance of the sweeping arc of arriving cars. Perhaps the notion of street parking feels safer? Perhaps this has to do with reducing risk (see next paragraph).

The most curious to me is the driver who parks close to, but not in, the next available spot. I suspect this entails a very quick calculation of risk. Let me explain. The process of parking involves a number of risks: fundamentally, you could hit someone else, or they could hit you (or both). Parking in a spot with no one on either side is the lowest risk for you (at least immediately), because there is virtually no way that you're going to hit someone else, either while parking or while opening your doors. On the other hand, parking in the next available spot encounters some risk: the chance of hitting the car next to you while parking or opening your door seems more likely. Lastly, squeezing into a spot with cars on both sides would appear to be the most risky from your standpoint, as you could hit more than one car.

So from the view of the driver, parking close to, but not in, the next available spot is a crude calculation that maximizes self-interest while minimizing the risk of hitting another vehicle. But wait, there's something missing here, and we've already touched on it. The risk is not only that you could hit someone else, but also that they could hit you. So let's return to our three scenarios, in reverse. Squeezing into a spot with cars on both sides would appear to be the most risky in terms of you hitting someone else, but the chances of those cars hitting you is nil because they're already parked. Parking in the next available spot is less risky to you as a driver but you're also passing a similar amount of risk to the next (future) driver who decides to park next to you. Finally, parking in a spot with no one on either side means that you're accepting virtually all of the risk that other drivers (who will eventually park on both sides of you) might hit you.

Let's simplify as much as possible and divide risk into two parts: the risk of you hitting someone else, and the risk of someone else hitting you. Furthermore, let's assume that on average, both of these are equally likely. This ignores the fact that drivers are probably, out of self-interest, more concerned about protecting their car than damaging another (even though in an accident both are probably going to occur).

If you are (more or less) of average driving and parking ability, it would make sense to take as much of the risk yourself, leaving nothing to the chance of some random, average driver. In this case, finding a spot with someone already on both sides is best. Next next would be to park in the next available spot, as you take perhaps half of the risk yourself and leave the remainder to the random, average driver. Lastly, parking in a spot with no one on either side seems to be the safest for yourself, but hands all of the risk off to both drivers who will inevitably park on either side of you. In your self-interest, to me this seems the worst option, yet it occurs quite a bit. Perhaps this is just an early morning decision based upon some notion of "out of sight, out of mind"?

Going back to the street-style spaces. If you were able to drive into one of these spaces rather than parallel park, you would have a curb on one side and the aisle of the parking lot on the other, so maybe this is the least risky of all of the options. Yet because they are further away, you're still sacrificing self-interest for lower risk.

I fully recognize that people do not drive into a parking lot with a head full of math, calculating risk to decide where to park; but I suspect people do have some preconceived notions about why they park where they do, and some of these notions may include some concepts of self-interest and risk.
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