Some people shared some other resources on a thread on the main list from earlier this year.
From @mkirk :
"I wanted to build a traffic counter to measure bicycle traffic in a few places around Los Angeles.
I came across this: http://tomorrow-lab.com/lab16 ...which is just such a thing touting:
We have made the parts list and Arduino code available under a Creative Commons License. We have developed multilingual How-To guides to allow anyone to build a DIY Traffic Counter.
But then I couldn't find their plans anywhere. After contacting the site administrator I was told they are now selling a revised model here: http://waycount.com/ .
They've also built some nice tooling around uploading the data and aggregating it into a central portal. Which is all cool stuff - but I'm interested in building my own sensor, and was disappointed that they took down the original instructions.
The basic design is a pneumatic tube connected to a differential pressure sensor. Results are logged onto the device. And the whole thing runs on a 9v battery for around 8 hours.
I was able to go to the way back machine and find a guide (yay internet archive!): https://web.archive.org/web/20160128041311/http://tomorrow-lab.com/traffic_counter/traffic_counter_guide.pdf But haven't yet tracked down the parts list, which wasn't indexed due to it being a GDoc. There are some links to parts at the end of the aforlinked guide (last page). I'm also missing the arduino software that works with the sensor.
Anyway - anyone have experience with this or a similar design? Or crosses fingers have the software?"
And Tim Pickering just shared this:
"I've just come across this thread, and with a bit of digging around, found https://github.com/codefordc/traffic_counter
which seems to be a fork of the original code, and a link to the instruction manual originally found on the wayback machine.
Just for anyone else looking. I've just ordered the parts, and will be testing it out asap..."