What is the secret behind the these small green boxes?

What is the secret behind the these small green boxes?

I've never been able to work out what they're for. There's no sign on them, no writing… they just appear in odd places

The retired public servant asked Curious Canberra to look into the green and sometimes grey boxes, and his question won our February voting round.

I'd seen the boxes Robert was asking about, they stand about a metre tall and can be found beside roads and on median strips.

Robert hadn't just been wondering about the boxes - he'd been photographing them too.



He emailed through a few examples, which helped me track down the person with the key to the boxes in question.

With a key in hand, the member of the traffic management and safety unit crouched down to unlock the rusty box we had come to see.

The box isn't completely empty though and we find a black power cable that runs down the length of the pole and into the ground.

At the other end is a round multi-pin connector. It plugs into a brick-like device that Pawel pulls from a canvas bag.

With the device plugged in and neatly stored in the box, the purpose of the unusual structures is almost revealed.

 The main idea is that they're always located on the major arterial road network

The counter inside the box monitors traffic flow and type by tapping into sensors that are buried in the road.

Every time a vehicle drives over it, the sensors detect that and measures the speed and volume

The boxes were originally installed by the National Capital Development Commission (NCDC) in the 1970's.

But even in their heyday, many of the metal boxes remained empty.

We would basically put the device in certain units and then the device would be removed, the data collected and they would be circulated through the other boxes

These days traffic monitoring technology is more portable, economical and accurate too.

At the bottom of the metal box we're inspecting we find a rectangular device that's is connected to two black tubes that stretch across the road.

 They're basically rubber loops with air inside and every time a vehicle drives over them the impulse gets sent to the box and gets recorded with a very simple computer,

The loops work in a similar way to the buried sensors and the data goes on to be interpreted by software.