This is not a rant about having to pay to park the car. I accept that, though there was less of it when I was young and it was better then. This is about arbitrary rules that can make the transaction almost a mathematical game.
The example is from the Water Gardens car park in Hemel Hempstead, or to more precise the lower floor of that car park - the upper floor has different rules allowing longer stays. The basic rules are: maximum stay 4 hours, buy ticket and display on vehicle, 50p for first hour than 30p per hour. Overstays, or any infraction against the rules result in a 60GBP penalty.
So, you arrive in the car park and expect to be about an hour. How much time do you buy? You have to guess just the once, because feeding the meter is not allowed. No, you cannot buy 2 hours in two 1-hour goes, even though that would cost 100p instead of 80p if bought at the start, and even though the stay is still less than the maximum 4 hours. So you have to decide up front.
So, if you play for safety and buy the maximum each time, and really need about an hour each time, then on average you'd waste 75p each time. And you have to get back inside four hours only 79 times out of 80 for this to be cheaper than paying a penalty charge. Most people would buy 2 hours, assuming that it's unlikely you'd be delayed that long, paying only 80p each time, but of course being much more likely to get a penalty if anything goes wrong. And still paying for twice the time that on average you use.
It's hard for pay-and-display to work with a fair pay-per-hour type system, unlike a pay-on-exit system, but why isn't it allowed to even approximate it? Why forbid topping up within the maximum stay? The attendants can still enforce maximum stay the same way they do with roadside free limited-time parking, by recording when first seen (or it could be time of issue of first ticket) and checking again after the expiry of the maximum time. It's just perversity, and of course it all helps to maximise revenue. This car park probably claims to be 50p/hour, but most people using it will be paying a lot more than that.
