A month of traffic counted

1 minute read


The We Count project distributes simple photo sensors for people to put on their street-facing windows so a computer can count how many vehicles, bikes and pedestrians pass by every day. Cities across Europe have people monitoring their streets. I got my sensor running at the end of November so I now have my first complete month of data.

Cardiff streets where monitoring is taking place The roads monitored in Cardiff through Telraam sensors (Jan 2021)

The sensor has been peering out my window for a month, counting the moving things it sees. What has it counted?

The data

The first thing we learn about this data is that sometimes it’s not very good. As explained on the project website, the sensor is never running 100% of the time. The data shows us (lightly paraphrased):

the percentage of time the Telraam camera was actively counting traffic in a one hour interval. This is almost never 100%, because in standard operation background calculation, intervals break the continuous measurements every couple of minutes for a half minute, and during this background calculation no active measurements are being carried out.

This appears to be a problem this month (December) from 4pm to 5pm because data is collected but it’s often not very good, presumably since the light is fading at this time of day. The sensor drops to ‘barely running at all’ and makes suspicious claims like ‘this hour there was an army of over fifty cyclists going one way down this quiet road (and, erm, nobody in the other direction)’.

So a day, for now, will have to just be the eight hours of good(ish) daylight from 8am to 4pm.

There are a lot of bicycles

A cyclist comes down the road every seven minutes on average in daylight hours. This can reach 20 bikes in a busy hour, or none if it’s quiet. The busiest day of the week is Saturday with usually more than 100 bikes during daylight and the quietest is Sunday (around 40).

That makes more than 2,000 cyclists passing this way over the month.

More analysis here (after two months)