A sensor over every bay, a red light for occupied and a green for free, and a count on the sign at the entrance that has to be right or people drive in and find nothing. One bay has been red for eight years with nothing under it.
I am a duty officer in the control room of a nine hundred space multi storey. Nights, four on four off, eleven years.
The bay sensors are what this is about.
Over every single bay there is an ultrasonic sensor in a little housing, and under the housing there is a light: red if the bay is taken, green if it is free. You have seen them in any modern car park. They exist so you can drive along a deck and see where to go instead of crawling round looking.
The sensor measures the distance to the floor. Empty bay, it sees the floor. Car in the bay, it sees the roof of the car, which is a good deal closer, and it reports occupied.
All of them report to a controller per deck, and the decks report to the system in my room, and the system drives the counts on the signs at the entrance and at the top of each ramp.
The count has to be right. A sign saying ninety free when there are nine is how you get a queue of angry people on a ramp at half past seven, and a sign saying nine when there are ninety is how you lose a day's takings.
Level 3, bay 7 has been occupied since the 14th of October 2017.
Eight years. The red light is on, the system counts it as a taken space, and the sign at the entrance is one lower than it should be.
There is no car in it.
I should say straight away what was done about it, because this was not ignored.
It was raised as a fault in 2017. The maintenance contractor replaced the sensor head. Still red.
They replaced the housing and the cable drop in 2018. Still red.
In 2019 they ran a new drop from a different port on the deck controller, which means that bay 7's sensor is now on a circuit that bay 7's sensor has never used before. Still red.
In 2021 the whole deck controller was replaced as part of a planned upgrade, and every bay on level 3 was commissioned from scratch, one at a time, with two men and a radio.
The commissioning record is a sheet with a tick per bay and a measured distance. Bay 7's measured distance is on that sheet. It is written as 1.4 metres.
Every other bay on that deck reads between 2.5 and 2.7 metres, which is the distance from the sensor to the concrete.
One point four metres from the sensor is the roof height of a car.
I have stood in bay 7 with a tape. Concrete, painted lines, a drain, the number 7 stencilled on the floor, and a sensor two and a bit metres above my head with a red light on it.
I have held a clipboard up at one point four metres and watched the light, which does nothing, because it is already red.
What I have also done, which took me an embarrassing number of years to think of, is stand in the next bay and hold the clipboard up at the same height. Bay 8 goes red, and goes green again when I take it away, within about two seconds.
So the sensors work. The one over bay 7 has been replaced three times and works in the sense that something is replying to it at one point four metres.
What is in the bay in the sense that matters to anybody.
Nothing. It is free. I could park in it.
And twice a week somebody does, because the bay is not coned off and people do not read lights. A car parks in bay 7 and the light is already red and nothing changes and nothing happens, and they come back and drive away.
I have watched that on camera dozens of times. A real car arrives in bay 7, sits there for three hours, and leaves, and the system's state for that bay does not change at any point, because it cannot get any more occupied than it already is.
The part I have never put in the log.
The camera on level 3 covers the ramp and about two thirds of the deck. Bay 7 is at the edge of frame, which is bad luck, and you can see the front half of the bay and the light.
On the 14th of October every year, the camera records something.
It is not dramatic and it would not convince anybody. Between about 02:40 and 02:55, at the edge of the frame, there is a change in the light on the floor of bay 7. The floor goes darker, in a shape, roughly the shape the shadow under a car makes, and there is a suggestion of something lighter above it that does not have edges you could draw.
And then it goes back to being concrete.
I have eight of those, because I save the clip every year. Four of them I have watched with another duty officer without telling him what he was looking at, and three of the four said they could not see anything and one of them said, is that the shadow of a car, and then said no, hang on.
What I do about it is the only thing the job allows.
Level 3 is ninety eight bays. The system counts ninety seven available on an empty night, and the sign at the entrance is one out across nine hundred spaces, which is a rounding error nobody will ever notice.
A previous duty manager, before my time, fixed the sign by adding one to the total in the configuration. It is still there, on a line labelled CALIBRATION +1, and it makes the entrance sign correct.
Which means that on a night when the car park genuinely fills, the sign says one space free when there is none, and somebody drives up nine decks looking for it.
That happens perhaps six times a year and those six drivers come back down and complain at the barrier and we wave them out for nothing, and I have never once in eleven years told any of them the real reason, which is that the space exists and it is on level 3 and it has been taken since 2017.