A DIY Traffic Counter being developed at Tomorrow Lab.
Made from about $70 in parts.
Keep a tally on bicycle traffic or car traffic using this device.
Made from an Arduino, differential air pressure sensor, 1/4" ID tubing, a check valve, batteries, and a speaker. The device beeps every time a bike is sensed, and keeps a total tally in its memory.
You can access the total tally later by attaching the device to a computer or by incorporating a display onto the device to show the current tally.
Get a materials list to build one here: