Bow Street, Cambridge
What is this small round sensor in the parking space?
It's a parking sensor. It does one thing: it tells whether a car is parked in this space. That's all it knows.
It's part of a short pilot on nine parking spaces on Bow Street, run by Harvard College students. The goal is to show drivers which spaces are free in real time, so fewer people circle the block looking for parking. You can see the live result at maps.gleepark.me.
Questions and answers
Does it use a camera?
No. There is no camera, no microphone and no license plate reader inside. It uses two simple sensors that both point straight up:
- A magnetometer, like the compass in a phone. A car is a large mass of metal, and it slightly changes the magnetic field when it parks on top.
- A low-power radar, like the kind used in automatic doors. It only checks whether something is sitting directly above the sensor.
Neither sensor can see a face, a person, a license plate or the make of a car. The device itself decides "occupied" or "free" and sends only that answer.
What information does it send, and who sees it?
Each message is 7 bytes, shorter than this sentence. It contains:
- whether the space is free or occupied,
- the time it changed, and
- the sensor's battery level.
The sensor sends a message only when a car arrives or leaves, plus one "still working" check-in every 12 hours. We store when each space became free or occupied so we can see how parking on Bow Street is used. We have no way to know whose car it was, and we collect no names, photos, plates or phone data.
The free/occupied status is public at maps.gleepark.me. The project is not connected to parking enforcement and cannot be used to issue tickets.
How is it attached? Can someone walk off with it?
It's bonded to the road surface with an outdoor adhesive made for raised lane markers, the same kind used to glue reflectors to roads. Nothing is drilled into the street, and it can't be pried off by hand.
When the pilot ends we remove the sensors and clean off the adhesive.
What about snow plowing and street cleaning?
This is a short, temporary pilot. We will remove every sensor before the first snow emergency, and earlier if Cambridge's Department of Public Works asks us to.
Until then we follow DPW's guidance on street cleaning. The sensor sits in the middle of the space with sloped edges and is built to be driven over.
Is the radio signal safe?
Yes. It uses LoRaWAN, a low-power radio standard used by utility meters. It transmits for less than a second at a time, a handful of times a day, at no more than 100 mW, which is below a typical cell phone. A short-range Bluetooth link is used only by our team to set up and calibrate the sensor. It doesn't look for or record nearby phones.
How long will it be here?
Only for the pilot, which ends no later than the first snow emergency of the winter. Every sensor is labelled with an ID and this page's address so it can be traced back to us.
Something's wrong with a sensor. What should I do?
If a sensor is loose, damaged or in the way, email us with the sensor ID printed on its label (or simply the space it's in) and we'll deal with it promptly.
Who runs this?
Albert Sveen, Max Lightfield and William Tang, students at Harvard College.
Questions, concerns or a problem with a sensor: asveen@college.harvard.edu
Email us